ported romeo patch from v0.2.2

original patch is 93e643a5fde01a9ca0538d9813957687c541de65

.github/workflows/ci.yml

@@ -17,10 +17,10 @@ jobs:
       matrix:
         rust:
           - stable
-          - 1.64.0
+          - 1.77.0
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install toolchain
         uses: dtolnay/rust-toolchain@master
@@ -30,63 +30,128 @@ jobs:
       - name: Run cargo check
         run: cargo check --all-features
 
+  build-wasm:
+    name: Build wasm32
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v4
+
+      - name: Install toolchain
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          targets: wasm32-unknown-unknown
+
+      - name: Run cargo build (wasm)
+        run: cargo build --target wasm32-unknown-unknown
+
   test:
     name: Test suite
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install toolchain
         uses: dtolnay/rust-toolchain@stable
 
       - name: Run cargo test
-        run: cargo test
+        run: cargo test --all-features
 
   loom-dry-run:
     name: Loom dry run
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install toolchain
         uses: dtolnay/rust-toolchain@stable
 
       - name: Dry-run cargo test (Loom)
-        run: cargo test --no-run --tests
+        run: cargo test --no-run --lib --all-features
         env:
-          RUSTFLAGS: --cfg asynchronix_loom
+          RUSTFLAGS: --cfg nexosim_loom
 
   miri:
     name: Miri
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install toolchain
         uses: dtolnay/rust-toolchain@nightly
         with:
           components: miri
 
-      - name: Run cargo miri tests
-        run: cargo miri test --tests --lib
+      - name: Run cargo miri tests (single-threaded executor)
+        run: cargo miri test --tests --lib --all-features
+        env:
+          MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=1
+
+      - name: Run cargo miri tests (multi-threaded executor)
+        run: cargo miri test --tests --lib --all-features
         env:
           MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=4
 
-      - name: Run cargo miri example1
+      - name: Run cargo miri espresso_machine (single-threaded executor)
+        run: cargo miri run --example espresso_machine
+        env:
+          MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=1
+
+      - name: Run cargo miri espresso_machine (multi-threaded executor)
         run: cargo miri run --example espresso_machine
         env:
           MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=4
 
-      - name: Run cargo miri example2
+      - name: Run cargo miri power_supply (single-threaded executor)
+        run: cargo miri run --example power_supply
+        env:
+          MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=1
+
+      - name: Run cargo miri power_supply (multi-threaded executor)
         run: cargo miri run --example power_supply
         env:
           MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=4
 
-      - name: Run cargo miri example3
+      - name: Run cargo miri stepper_motor (single-threaded executor)
         run: cargo miri run --example stepper_motor
+        env:
+          MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=1
+
+      - name: Run cargo miri stepper_motor (multi-threaded executor)
+        run: cargo miri run --example stepper_motor
+        env:
+          MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=4
+
+      - name: Run cargo miri assembly (single-threaded executor)
+        run: cargo miri run --example assembly
+        env:
+          MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=1
+
+      - name: Run cargo miri assembly (multi-threaded executor)
+        run: cargo miri run --example assembly
+        env:
+          MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=4
+
+      - name: Run cargo miri uni_requestor (single-threaded executor)
+        run: cargo miri run --example uni_requestor
+        env:
+          MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=1
+
+      - name: Run cargo miri uni_requestor (multi-threaded executor)
+        run: cargo miri run --example uni_requestor
+        env:
+          MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=4
+
+      - name: Run cargo miri observables (single-threaded executor)
+        run: cargo miri run --example observables
+        env:
+          MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=1
+
+      - name: Run cargo miri observables (multi-threaded executor)
+        run: cargo miri run --example observables
         env:
           MIRIFLAGS: -Zmiri-strict-provenance -Zmiri-disable-isolation -Zmiri-num-cpus=4
 
@@ -95,7 +160,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install toolchain
         uses: dtolnay/rust-toolchain@stable
@@ -104,17 +169,22 @@ jobs:
         run: cargo fmt --all -- --check
 
       - name: Run cargo clippy
-        run: cargo clippy
+        run: |
+          cargo clippy --tests --all-features
+          # See PR#75: https://github.com/asynchronics/nexosim/pull/75
+          cargo clippy --examples --all-features -- -A clippy::new_without_default -A clippy::manual_async_fn
 
   docs:
     name: Docs
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@nightly
 
       - name: Run cargo doc
-        run: cargo doc --no-deps --document-private-items
+        run: cargo doc --no-deps --all-features --document-private-items
+        env:
+            RUSTDOCFLAGS: --cfg docsrs -Dwarnings

.github/workflows/loom.yml

@@ -1,20 +1,36 @@
 name: Loom
 
 on:
+  workflow_dispatch:
   pull_request:
+    paths:
+      - 'nexosim/src/channel.rs'
+      - 'nexosim/src/channel/**'
+      - 'nexosim/src/executor/task.rs'
+      - 'nexosim/src/executor/task/**'
+      - 'nexosim/src/loom_exports.rs'
+      - 'nexosim/src/ports/output/broadcaster.rs'
+      - 'nexosim/src/ports/output/broadcaster/**'
+      - 'nexosim/src/ports/source/broadcaster.rs'
+      - 'nexosim/src/ports/source/broadcaster/**'
+      - 'nexosim/src/util/cached_rw_lock.rs'
+      - 'nexosim/src/util/slot.rs'
+      - 'nexosim/src/util/sync_cell.rs'
   push:
     branches: [ main ]
     paths:
-      - 'asynchronix/src/channel.rs'
-      - 'asynchronix/src/channel/**'
-      - 'asynchronix/src/executor/task.rs'
-      - 'asynchronix/src/executor/task/**'
-      - 'asynchronix/src/loom_exports.rs'
-      - 'asynchronix/src/model/ports/broadcaster.rs'
-      - 'asynchronix/src/model/ports/broadcaster/**'
-      - 'asynchronix/src/util/slot.rs'
-      - 'asynchronix/src/util/spsc_queue.rs'
-      - 'asynchronix/src/util/sync_cell.rs'
+      - 'nexosim/src/channel.rs'
+      - 'nexosim/src/channel/**'
+      - 'nexosim/src/executor/task.rs'
+      - 'nexosim/src/executor/task/**'
+      - 'nexosim/src/loom_exports.rs'
+      - 'nexosim/src/ports/output/broadcaster.rs'
+      - 'nexosim/src/ports/output/broadcaster/**'
+      - 'nexosim/src/ports/source/broadcaster.rs'
+      - 'nexosim/src/ports/source/broadcaster/**'
+      - 'nexosim/src/util/cached_rw_lock.rs'
+      - 'nexosim/src/util/slot.rs'
+      - 'nexosim/src/util/sync_cell.rs'
 
 jobs:
   loom:
@@ -22,12 +38,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install toolchain
         uses: dtolnay/rust-toolchain@stable
 
       - name: Run cargo test (Loom)
-        run: cargo test --tests --release
+        run: cargo test --lib --release
         env:
-          RUSTFLAGS: --cfg asynchronix_loom
+          RUSTFLAGS: --cfg nexosim_loom

CHANGELOG.md

@@ -1,10 +1,117 @@
+# 0.3.1 (2025-01-28)
+
+- Add a blocking event queue ([#82]).
+
+[#82]: https://github.com/asynchronics/nexosim/pull/82
+
+
+# 0.3.0 (2025-01-20)
+
+The final 0.3.0 release features a very large number of improvements and API
+changes, including all those in the beta release and a couple more.
+
+This release is not compatible with the 0.2.* releases, but porting models and benches should be relatively straightforward.
+
+### Added (mostly API-breaking changes)
+
+- Add a gRPC server for local (Unix Domain Sockets) and remote (http/2)
+  execution ([#12], [#24], [#25], [#26], [#29], [#43], [#78], [#79])
+- Single-threaded executor supporting compilation to WebAssembly ([#24])
+- Add support for the `tracing` crate ([#47])
+- Make `Output`s and `Requestor`s `Clone`-able ([#30], [#48])
+- Make the global `Scheduler` an owned `Clone`-able type that can be sent to
+  other threads ([#30])
+- Add an automatically managed action key for scheduled actions/events ([#27])
+- Enable connection of different input/output pairs with `map_connect()` methods
+  on `Output` and `Requestor` ([#32])
+- Streamline the creation of data buses (SPI, CAN, MIL-STD-1553, SpaceWire etc.)
+  with `filter_map_connect()` methods on `Output` and `Requestor` ([#32])
+- Implement deadlock detection ([#51])
+- Streamline the builder pattern for models with a `ProtoModel` trait ([#54])
+- Implement execution timeout ([#57])
+- Return an error when a real-time simulation clock looses synchronization
+  ([#58])
+- Catch model panics and report them as errors ([#60])
+- Provide additional ordering guaranties when using the global scheduler ([#62])
+- Remove `LineId` line disconnection API ([#63])
+- Implement detection of lost and undelivered messages ([#68], [#70])
+- Provide a `UniRequestor` type for unary requestors ([#69])
+- Add support for intentionally halting an ongoing simulation and add a
+  `Simulation::step_unbounded` method ([#74], [#77])
+
+[#68]: https://github.com/asynchronics/nexosim/pull/68
+[#69]: https://github.com/asynchronics/nexosim/pull/69
+[#70]: https://github.com/asynchronics/nexosim/pull/70
+[#74]: https://github.com/asynchronics/nexosim/pull/74
+[#77]: https://github.com/asynchronics/nexosim/pull/77
+[#78]: https://github.com/asynchronics/nexosim/pull/78
+[#79]: https://github.com/asynchronics/nexosim/pull/79
+
+
+# 0.3.0-beta.0 (2024-11-16)
+
+This beta release features a very large number of improvements and API changes,
+including:
+
+- Add a gRPC server for remote execution ([#12], [#24], [#25], [#26], [#29],
+  [#43])
+- Single-threaded executor supporting compilation to WebAssembly ([#24])
+- Add support for the `tracing` crate ([#47])
+- Make `Output`s and `Requestor`s `Clone`-able ([#30], [#48])
+- Make the global `Scheduler` an owned `Clone`-able type ([#30])
+- Add an automatically managed action key for scheduled actions/events ([#27])
+- Enable connection of different input/output pairs with `map_connect()` methods
+  on `Output` and `Requestor` ([#32])
+- Streamline the creation of data buses (SPI, CAN, MIL-STD-1553, SpaceWire etc.)
+  with `filter_map_connect()` methods on `Output` and `Requestor` ([#32])
+- Implement deadlock detection ([#51])
+- Streamline the builder pattern for models with a `ProtoModel` trait ([#54])
+- Implement execution timeout ([#57])
+- Return an error when a real-time simulation clock looses synchronization
+  ([#58])
+- Catch model panics and report them as errors ([#60])
+- Provide additional ordering guaranties when using the global scheduler ([#62])
+- Remove `LineId` line disconnection API ([#63])
+
+[#12]: https://github.com/asynchronics/nexosim/pull/12
+[#24]: https://github.com/asynchronics/nexosim/pull/24
+[#25]: https://github.com/asynchronics/nexosim/pull/25
+[#26]: https://github.com/asynchronics/nexosim/pull/26
+[#27]: https://github.com/asynchronics/nexosim/pull/27
+[#29]: https://github.com/asynchronics/nexosim/pull/29
+[#30]: https://github.com/asynchronics/nexosim/pull/30
+[#32]: https://github.com/asynchronics/nexosim/pull/32
+[#43]: https://github.com/asynchronics/nexosim/pull/43
+[#47]: https://github.com/asynchronics/nexosim/pull/47
+[#48]: https://github.com/asynchronics/nexosim/pull/48
+[#51]: https://github.com/asynchronics/nexosim/pull/51
+[#54]: https://github.com/asynchronics/nexosim/pull/54
+[#57]: https://github.com/asynchronics/nexosim/pull/57
+[#58]: https://github.com/asynchronics/nexosim/pull/58
+[#60]: https://github.com/asynchronics/nexosim/pull/60
+[#62]: https://github.com/asynchronics/nexosim/pull/62
+[#63]: https://github.com/asynchronics/nexosim/pull/63
+
+# 0.2.4 (2024-11-16)
+
+- Add crate rename notice
+
+# 0.2.3 (2024-08-24)
+
+- Force the waker VTable to be uniquely instantiated to re-enable the
+  `will_wake` optimisation after its implementation was changed in `std` ([#38])
+- Ignore broadcast error when sending to a closed `EventStream` ([#37])
+
+[#37]: https://github.com/asynchronics/nexosim/pull/37
+[#38]: https://github.com/asynchronics/nexosim/pull/38
+
 # 0.2.2 (2024-04-04)
 
 - Add `serde` feature and serialization support for `MonotonicTime` ([#19]).
 - Update `multishot` dependency due to soundness issue in older version ([#23]).
 
-[#19]: https://github.com/asynchronics/asynchronix/pull/19
-[#23]: https://github.com/asynchronics/asynchronix/pull/23
+[#19]: https://github.com/asynchronics/nexosim/pull/19
+[#23]: https://github.com/asynchronics/nexosim/pull/23
 
 # 0.2.1 (2024-03-06)
 
@@ -13,8 +120,8 @@
 - Add support for custom clocks and provide an optional real-time clock
   ([#9], [#15]).
 
-[#9]: https://github.com/asynchronics/asynchronix/pull/9
-[#15]: https://github.com/asynchronics/asynchronix/pull/15
+[#9]: https://github.com/asynchronics/nexosim/pull/9
+[#15]: https://github.com/asynchronics/nexosim/pull/15
 
 ### Misc
 
@@ -33,9 +140,9 @@
   `schedule_*event` method that accept either a `Duration` or a `MonotonicTime`
   ([#7]).
 
-[#5]: https://github.com/asynchronics/asynchronix/pull/5
-[#6]: https://github.com/asynchronics/asynchronix/pull/6
-[#7]: https://github.com/asynchronics/asynchronix/pull/7
+[#5]: https://github.com/asynchronics/nexosim/pull/5
+[#6]: https://github.com/asynchronics/nexosim/pull/6
+[#7]: https://github.com/asynchronics/nexosim/pull/7
 
 
 # 0.1.0 (2023-01-16)

Cargo.toml

@@ -1,3 +1,3 @@
 [workspace]
-members = ["asynchronix"]
+members = ["nexosim", "nexosim-util"]
 resolver = "2"

LICENSE-MIT

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2024 Asynchronics sp. z o.o. and Asynchronix Contributors
+Copyright (c) 2025 Asynchronics sp. z o.o. and NeXosim Contributors
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -1,17 +1,23 @@
-# Asynchronix
+# NeXosim
 
-Asynchronix is a developer-friendly, highly optimized discrete-event simulation
-framework written in Rust. It is meant to scale from small, simple simulations
-to very large simulation benches with complex time-driven state machines.
+NeXosim (né Asynchronix) is a developer-friendly, highly optimized
+discrete-event simulation framework written in Rust. It is meant to scale from
+small, simple simulations to very large simulation benches with complex
+time-driven state machines.
 
-[![Cargo](https://img.shields.io/crates/v/asynchronix.svg)](https://crates.io/crates/asynchronix)
-[![Documentation](https://docs.rs/asynchronix/badge.svg)](https://docs.rs/asynchronix)
-[![License](https://img.shields.io/badge/license-MIT%2FApache--2.0-blue.svg)](https://github.com/asynchronics/asynchronix#license)
+
+## 🎉🥳 NeXosim 0.3.1 is out! 🚀🛰️
+
+See the [changelog](CHANGELOG.md) for a summary of new features, or head to the extensive [API documentation][API] for the details.
+
+[![Cargo](https://img.shields.io/crates/v/nexosim.svg)](https://crates.io/crates/nexosim)
+[![Documentation](https://docs.rs/nexosim/badge.svg)](https://docs.rs/nexosim)
+[![License](https://img.shields.io/badge/license-MIT%2FApache--2.0-blue.svg)](https://github.com/asynchronics/nexosim#license)
 
 
 ## Overview
 
-Asynchronix is a simulator that leverages asynchronous programming to
+NeXosim is a simulator that leverages asynchronous programming to
 transparently and efficiently auto-parallelize simulations by means of a custom
 multi-threaded executor.
 
@@ -22,7 +28,7 @@ communicating with other models through message passing via connections defined
 during bench assembly.
 
 Although the main impetus for its development was the need for simulators able
-to handle large cyberphysical systems, Asynchronix is a general-purpose
+to handle large cyberphysical systems, NeXosim is a general-purpose
 discrete-event simulator expected to be suitable for a wide range of simulation
 activities. It draws from experience on spacecraft real-time simulators but
 differs from existing tools in the space industry in a number of respects,
@@ -35,7 +41,7 @@ including:
 2) *developer-friendliness*: an ergonomic API and Rust's support for algebraic
    types make it ideal for the "cyber" part in cyberphysical, i.e. for modelling
    digital devices with even very complex state machines,
-3) *open-source*: last but not least, Asynchronix is distributed under the very
+3) *open-source*: last but not least, NeXosim is distributed under the very
    permissive MIT and Apache 2 licenses, with the explicit intent to foster an
    ecosystem where models can be easily exchanged without reliance on
    proprietary APIs.
@@ -49,18 +55,19 @@ The [API] documentation is relatively exhaustive and includes a practical
 overview which should provide all necessary information to get started.
 
 More fleshed out examples can also be found in the dedicated
-[directory](asynchronix/examples).
+[simulator](nexosim/examples) and [utilities](nexosim-util/examples)
+directories.
 
-[API]: https://docs.rs/asynchronix
+[API]: https://docs.rs/nexosim
 
 
 ## Usage
 
-Add this to your `Cargo.toml`:
+To use the latest version, add to your `Cargo.toml`:
 
 ```toml
 [dependencies]
-asynchronix = "0.2.2"
+nexosim = "0.3.1"
 ```
 
 
@@ -72,23 +79,24 @@ asynchronix = "0.2.2"
 //
 //              ┌──────────────┐      ┌──────────────┐
 //              │              │      │              │
-// Input ●─────▶│ multiplier 1 ├─────▶│ multiplier 2 ├─────▶ Output
+// Input ●─────►│ multiplier 1 ├─────►│ multiplier 2 ├─────► Output
 //              │              │      │              │
 //              └──────────────┘      └──────────────┘
-use asynchronix::model::{Model, Output};
-use asynchronix::simulation::{Mailbox, SimInit};
-use asynchronix::time::{MonotonicTime, Scheduler};
 use std::time::Duration;
 
+use nexosim::model::{Context, Model};
+use nexosim::ports::{EventSlot, Output};
+use nexosim::simulation::{Mailbox, SimInit};
+use nexosim::time::MonotonicTime;
+
 // A model that doubles its input and forwards it with a 1s delay.
 #[derive(Default)]
 pub struct DelayedMultiplier {
     pub output: Output<f64>,
 }
 impl DelayedMultiplier {
-    pub fn input(&mut self, value: f64, scheduler: &Scheduler<Self>) {
-        scheduler
-            .schedule_event(Duration::from_secs(1), Self::send, 2.0 * value)
+    pub fn input(&mut self, value: f64, ctx: &mut Context<Self>) {
+        ctx.schedule_event(Duration::from_secs(1), Self::send, 2.0 * value)
             .unwrap();
     }
     async fn send(&mut self, value: f64) {
@@ -109,33 +117,35 @@ multiplier1
     .connect(DelayedMultiplier::input, &multiplier2_mbox);
 
 // Keep handles to the main input and output.
-let mut output_slot = multiplier2.output.connect_slot().0;
+let mut output_slot = EventSlot::new();
+multiplier2.output.connect_sink(&output_slot);
 let input_address = multiplier1_mbox.address();
 
 // Instantiate the simulator
 let t0 = MonotonicTime::EPOCH; // arbitrary start time
 let mut simu = SimInit::new()
-    .add_model(multiplier1, multiplier1_mbox)
-    .add_model(multiplier2, multiplier2_mbox)
-    .init(t0);
+    .add_model(multiplier1, multiplier1_mbox, "multiplier 1")
+    .add_model(multiplier2, multiplier2_mbox, "multiplier 2")
+    .init(t0)?
+    .0;
 
 // Send a value to the first multiplier.
-simu.send_event(DelayedMultiplier::input, 3.5, &input_address);
+simu.process_event(DelayedMultiplier::input, 3.5, &input_address)?;
 
 // Advance time to the next event.
-simu.step();
+simu.step()?;
 assert_eq!(simu.time(), t0 + Duration::from_secs(1));
-assert_eq!(output_slot.take(), None);
+assert_eq!(output_slot.next(), None);
 
 // Advance time to the next event.
-simu.step();
+simu.step()?;
 assert_eq!(simu.time(), t0 + Duration::from_secs(2));
-assert_eq!(output_slot.take(), Some(14.0));
+assert_eq!(output_slot.next(), Some(14.0));
 ```
 
 # Implementation notes
 
-Under the hood, Asynchronix is based on an asynchronous implementation of the
+Under the hood, NeXosim is based on an asynchronous implementation of the
 [actor model][actor_model], where each simulation model is an actor. The
 messages actually exchanged between models are `async` closures which capture
 the event's or request's value and take the model as `&mut self` argument. The
@@ -153,13 +163,13 @@ asynchronous runtimes such as [Tokio][tokio], because the end of a set of
 computations is technically a deadlock: the computation completes when all model
 have nothing left to do and are blocked on an empty mailbox. Also, instead of
 managing a conventional reactor, the runtime manages a priority queue containing
-the posted events. For these reasons, Asynchronix relies on a fully custom
+the posted events. For these reasons, NeXosim relies on a fully custom
 runtime.
 
 Even though the runtime was largely influenced by Tokio, it features additional
 optimizations that make its faster than any other multi-threaded Rust executor
 on the typically message-passing-heavy workloads seen in discrete-event
-simulation (see [benchmark]). Asynchronix also improves over the state of the
+simulation (see [benchmark]). NeXosim also improves over the state of the
 art with a very fast custom MPSC channel, which performance has been
 demonstrated through [Tachyonix][tachyonix], a general-purpose offshoot of this
 channel.

asynchronix/Cargo.toml

@@ -1,59 +0,0 @@
-[package]
-name = "asynchronix"
-# When incrementing version and releasing to crates.io:
-# - Update crate version in this Cargo.toml
-# - Update crate version in README.md
-# - Update CHANGELOG.md
-# - Update if necessary copyright notice in LICENSE-MIT
-# - Create a "vX.Y.Z" git tag
-authors = ["Serge Barral <serge.barral@asynchronics.com>"]
-version = "0.2.2"
-edition = "2021"
-rust-version = "1.64"
-license = "MIT OR Apache-2.0"
-repository = "https://github.com/asynchronics/asynchronix"
-readme = "../README.md"
-description = """
-A high performance asychronous compute framework for system simulation.
-"""
-categories = ["simulation", "aerospace", "science"]
-keywords = ["simulation", "discrete-event", "systems", "cyberphysical", "real-time"]
-autotests = false
-
-[features]
-serde = ["dep:serde"]
-# API-unstable public exports meant for external test/benchmarking; development only.
-dev-hooks = []
-# Logging of performance-related statistics; development only.
-dev-logs = []
-
-[dependencies]
-async-event = "0.1"
-crossbeam-utils = "0.8"
-diatomic-waker = "0.1"
-futures-task = "0.3"
-multishot = "0.3.2"
-num_cpus = "1.13"
-pin-project-lite = "0.2"
-recycle-box = "0.2"
-slab = "0.4"
-spin_sleep = "1"
-st3 = "0.4"
-
-[dependencies.serde]
-version = "1"
-optional = true
-features = ["derive"]
-
-[target.'cfg(asynchronix_loom)'.dependencies]
-loom = "0.5"
-waker-fn = "1.1"
-
-[dev-dependencies]
-futures-util = "0.3"
-futures-channel = "0.3"
-futures-executor = "0.3"
-
-[[test]]
-name = "integration"
-path = "tests/tests.rs"

asynchronix/src/executor/task/tests.rs

@@ -1,7 +0,0 @@
-use super::*;
-
-#[cfg(not(asynchronix_loom))]
-mod general;
-
-#[cfg(asynchronix_loom)]
-mod loom;

asynchronix/src/executor/tests.rs

@@ -1,140 +0,0 @@
-use futures_channel::{mpsc, oneshot};
-use futures_util::StreamExt;
-
-use super::*;
-
-/// An object that runs an arbitrary closure when dropped.
-struct RunOnDrop<F: FnOnce()> {
-    drop_fn: Option<F>,
-}
-impl<F: FnOnce()> RunOnDrop<F> {
-    /// Creates a new `RunOnDrop`.
-    fn new(drop_fn: F) -> Self {
-        Self {
-            drop_fn: Some(drop_fn),
-        }
-    }
-}
-impl<F: FnOnce()> Drop for RunOnDrop<F> {
-    fn drop(&mut self) {
-        self.drop_fn.take().map(|f| f());
-    }
-}
-
-#[test]
-fn executor_deadlock() {
-    const NUM_THREADS: usize = 3;
-
-    let (_sender1, receiver1) = oneshot::channel::<()>();
-    let (_sender2, receiver2) = oneshot::channel::<()>();
-
-    let mut executor = Executor::new(NUM_THREADS);
-    static LAUNCH_COUNT: AtomicUsize = AtomicUsize::new(0);
-    static COMPLETION_COUNT: AtomicUsize = AtomicUsize::new(0);
-
-    executor.spawn_and_forget(async move {
-        LAUNCH_COUNT.fetch_add(1, Ordering::Relaxed);
-        let _ = receiver2.await;
-        COMPLETION_COUNT.fetch_add(1, Ordering::Relaxed);
-    });
-    executor.spawn_and_forget(async move {
-        LAUNCH_COUNT.fetch_add(1, Ordering::Relaxed);
-        let _ = receiver1.await;
-        COMPLETION_COUNT.fetch_add(1, Ordering::Relaxed);
-    });
-
-    executor.run();
-    // Check that the executor returns on deadlock, i.e. none of the task has
-    // completed.
-    assert_eq!(LAUNCH_COUNT.load(Ordering::Relaxed), 2);
-    assert_eq!(COMPLETION_COUNT.load(Ordering::Relaxed), 0);
-}
-
-#[test]
-fn executor_deadlock_st() {
-    const NUM_THREADS: usize = 1;
-
-    let (_sender1, receiver1) = oneshot::channel::<()>();
-    let (_sender2, receiver2) = oneshot::channel::<()>();
-
-    let mut executor = Executor::new(NUM_THREADS);
-    static LAUNCH_COUNT: AtomicUsize = AtomicUsize::new(0);
-    static COMPLETION_COUNT: AtomicUsize = AtomicUsize::new(0);
-
-    executor.spawn_and_forget(async move {
-        LAUNCH_COUNT.fetch_add(1, Ordering::Relaxed);
-        let _ = receiver2.await;
-        COMPLETION_COUNT.fetch_add(1, Ordering::Relaxed);
-    });
-    executor.spawn_and_forget(async move {
-        LAUNCH_COUNT.fetch_add(1, Ordering::Relaxed);
-        let _ = receiver1.await;
-        COMPLETION_COUNT.fetch_add(1, Ordering::Relaxed);
-    });
-
-    executor.run();
-    // Check that the executor returnes on deadlock, i.e. none of the task has
-    // completed.
-    assert_eq!(LAUNCH_COUNT.load(Ordering::Relaxed), 2);
-    assert_eq!(COMPLETION_COUNT.load(Ordering::Relaxed), 0);
-}
-
-#[test]
-fn executor_drop_cycle() {
-    const NUM_THREADS: usize = 3;
-
-    let (sender1, mut receiver1) = mpsc::channel(2);
-    let (sender2, mut receiver2) = mpsc::channel(2);
-    let (sender3, mut receiver3) = mpsc::channel(2);
-
-    let mut executor = Executor::new(NUM_THREADS);
-    static DROP_COUNT: AtomicUsize = AtomicUsize::new(0);
-
-    // Spawn 3 tasks that wake one another when dropped.
-    executor.spawn_and_forget({
-        let mut sender2 = sender2.clone();
-        let mut sender3 = sender3.clone();
-
-        async move {
-            let _guard = RunOnDrop::new(move || {
-                let _ = sender2.try_send(());
-                let _ = sender3.try_send(());
-                DROP_COUNT.fetch_add(1, Ordering::Relaxed);
-            });
-            let _ = receiver1.next().await;
-        }
-    });
-    executor.spawn_and_forget({
-        let mut sender1 = sender1.clone();
-        let mut sender3 = sender3.clone();
-
-        async move {
-            let _guard = RunOnDrop::new(move || {
-                let _ = sender1.try_send(());
-                let _ = sender3.try_send(());
-                DROP_COUNT.fetch_add(1, Ordering::Relaxed);
-            });
-            let _ = receiver2.next().await;
-        }
-    });
-    executor.spawn_and_forget({
-        let mut sender1 = sender1.clone();
-        let mut sender2 = sender2.clone();
-
-        async move {
-            let _guard = RunOnDrop::new(move || {
-                let _ = sender1.try_send(());
-                let _ = sender2.try_send(());
-                DROP_COUNT.fetch_add(1, Ordering::Relaxed);
-            });
-            let _ = receiver3.next().await;
-        }
-    });
-
-    executor.run();
-
-    // Make sure that all tasks are eventually dropped even though each task
-    // wakes the others when dropped.
-    drop(executor);
-    assert_eq!(DROP_COUNT.load(Ordering::Relaxed), 3);
-}

asynchronix/src/executor/worker.rs

@@ -1,25 +0,0 @@
-use std::cell::Cell;
-use std::sync::Arc;
-
-use super::task::Runnable;
-
-use super::ExecutorContext;
-use super::LocalQueue;
-
-/// A local worker with access to global executor resources.
-pub(crate) struct Worker {
-    pub(super) local_queue: LocalQueue,
-    pub(super) fast_slot: Cell<Option<Runnable>>,
-    pub(super) executor_context: Arc<ExecutorContext>,
-}
-
-impl Worker {
-    /// Creates a new worker.
-    pub(super) fn new(local_queue: LocalQueue, executor_context: Arc<ExecutorContext>) -> Self {
-        Self {
-            local_queue,
-            fast_slot: Cell::new(None),
-            executor_context,
-        }
-    }
-}

asynchronix/src/model.rs

@@ -1,253 +0,0 @@
-//! Model components.
-//!
-//! # Model trait
-//!
-//! Every model must implement the [`Model`] trait. This trait defines an
-//! asynchronous initialization method, [`Model::init()`], which main purpose is
-//! to enable models to perform specific actions only once all models have been
-//! connected and migrated to the simulation, but before the simulation actually
-//! starts.
-//!
-//! #### Examples
-//!
-//! A model that does not require initialization can simply use the default
-//! implementation of the `Model` trait:
-//!
-//! ```
-//! use asynchronix::model::Model;
-//!
-//! pub struct MyModel {
-//!     // ...
-//! }
-//! impl Model for MyModel {}
-//! ```
-//!
-//! Otherwise, a custom `init()` method can be implemented:
-//!
-//! ```
-//! use std::future::Future;
-//! use std::pin::Pin;
-//!
-//! use asynchronix::model::{InitializedModel, Model};
-//! use asynchronix::time::Scheduler;
-//!
-//! pub struct MyModel {
-//!     // ...
-//! }
-//! impl Model for MyModel {
-//!     fn init(
-//!         mut self,
-//!         scheduler: &Scheduler<Self>
-//!     ) -> Pin<Box<dyn Future<Output = InitializedModel<Self>> + Send + '_>>{
-//!         Box::pin(async move {
-//!             println!("...initialization...");
-//!
-//!             self.into()
-//!         })
-//!     }
-//! }
-//! ```
-//!
-//! # Events and queries
-//!
-//! Models can exchange data via *events* and *queries*.
-//!
-//! Events are send-and-forget messages that can be broadcast from an *output
-//! port* to an arbitrary number of *input ports* with a matching event type.
-//!
-//! Queries actually involve two messages: a *request* that can be broadcast
-//! from a *requestor port* to an arbitrary number of *replier ports* with a
-//! matching request type, and a *reply* sent in response to such request. The
-//! response received by a requestor port is an iterator that yields as many
-//! items (replies) as there are connected replier ports.
-//!
-//!
-//! ### Output and requestor ports
-//!
-//! Output and requestor ports can be added to a model using composition, adding
-//! [`Output`] and [`Requestor`] objects as members. They are parametrized by
-//! the event, request and reply types.
-//!
-//! Models are expected to expose their output and requestor ports as public
-//! members so they can be connected to input and replier ports when assembling
-//! the simulation bench.
-//!
-//! #### Example
-//!
-//! ```
-//! use asynchronix::model::{Model, Output, Requestor};
-//!
-//! pub struct MyModel {
-//!     pub my_output: Output<String>,
-//!     pub my_requestor: Requestor<u32, bool>,
-//! }
-//! impl MyModel {
-//!     // ...
-//! }
-//! impl Model for MyModel {}
-//! ```
-//!
-//!
-//! ### Input and replier ports
-//!
-//! Input ports and replier ports are methods that implement the [`InputFn`] or
-//! [`ReplierFn`] traits with appropriate bounds on their argument and return
-//! types.
-//!
-//! In practice, an input port method for an event of type `T` may have any of
-//! the following signatures, where the futures returned by the `async` variants
-//! must implement `Send`:
-//!
-//! ```ignore
-//! fn(&mut self) // argument elided, implies `T=()`
-//! fn(&mut self, T)
-//! fn(&mut self, T, &Scheduler<Self>)
-//! async fn(&mut self) // argument elided, implies `T=()`
-//! async fn(&mut self, T)
-//! async fn(&mut self, T, &Scheduler<Self>)
-//! where
-//!     Self: Model,
-//!     T: Clone + Send + 'static,
-//!     R: Send + 'static,
-//! ```
-//!
-//! The scheduler argument is useful for methods that need access to the
-//! simulation time or that need to schedule an action at a future date.
-//!
-//! A replier port for a request of type `T` with a reply of type `R` may in
-//! turn have any of the following signatures, where the futures must implement
-//! `Send`:
-//!
-//! ```ignore
-//! async fn(&mut self) -> R // argument elided, implies `T=()`
-//! async fn(&mut self, T) -> R
-//! async fn(&mut self, T, &Scheduler<Self>) -> R
-//! where
-//!     Self: Model,
-//!     T: Clone + Send + 'static,
-//!     R: Send + 'static,
-//! ```
-//!
-//! Output and replier ports will normally be exposed as public methods so they
-//! can be connected to input and requestor ports when assembling the simulation
-//! bench. However, input ports may instead be defined as private methods if
-//! they are only used by the model itself to schedule future actions (see the
-//! [`Scheduler`](crate::time::Scheduler) examples).
-//!
-//! Changing the signature of an input or replier port is not considered to
-//! alter the public interface of a model provided that the event, request and
-//! reply types remain the same.
-//!
-//! #### Example
-//!
-//! ```
-//! use asynchronix::model::Model;
-//! use asynchronix::time::Scheduler;
-//!
-//! pub struct MyModel {
-//!     // ...
-//! }
-//! impl MyModel {
-//!     pub fn my_input(&mut self, input: String, scheduler: &Scheduler<Self>) {
-//!         // ...
-//!     }
-//!     pub async fn my_replier(&mut self, request: u32) -> bool { // scheduler argument elided
-//!         // ...
-//!         # unimplemented!()
-//!     }
-//! }
-//! impl Model for MyModel {}
-//! ```
-//!
-
-use std::future::Future;
-use std::pin::Pin;
-
-use crate::time::Scheduler;
-
-pub use model_fn::{InputFn, ReplierFn};
-pub use ports::{LineError, LineId, Output, Requestor};
-
-pub mod markers;
-mod model_fn;
-mod ports;
-
-/// Trait to be implemented by all models.
-///
-/// This trait enables models to perform specific actions in the
-/// [`Model::init()`] method only once all models have been connected and
-/// migrated to the simulation bench, but before the simulation actually starts.
-/// A common use for `init` is to send messages to connected models at the
-/// beginning of the simulation.
-///
-/// The `init` function converts the model to the opaque `InitializedModel` type
-/// to prevent an already initialized model from being added to the simulation
-/// bench.
-pub trait Model: Sized + Send + 'static {
-    /// Performs asynchronous model initialization.
-    ///
-    /// This asynchronous method is executed exactly once for all models of the
-    /// simulation when the
-    /// [`SimInit::init()`](crate::simulation::SimInit::init) method is called.
-    ///
-    /// The default implementation simply converts the model to an
-    /// `InitializedModel` without any side effect.
-    ///
-    /// *Note*: it is currently necessary to box the returned future; this
-    /// limitation will be lifted once Rust supports `async` methods in traits.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::future::Future;
-    /// use std::pin::Pin;
-    ///
-    /// use asynchronix::model::{InitializedModel, Model};
-    /// use asynchronix::time::Scheduler;
-    ///
-    /// pub struct MyModel {
-    ///     // ...
-    /// }
-    ///
-    /// impl Model for MyModel {
-    ///     fn init(
-    ///         self,
-    ///         scheduler: &Scheduler<Self>
-    ///     ) -> Pin<Box<dyn Future<Output = InitializedModel<Self>> + Send + '_>>{
-    ///         Box::pin(async move {
-    ///             println!("...initialization...");
-    ///
-    ///             self.into()
-    ///         })
-    ///     }
-    /// }
-    /// ```
-
-    // Removing the boxing constraint requires the
-    // `return_position_impl_trait_in_trait` and `async_fn_in_trait` features.
-    // Tracking issue: <https://github.com/rust-lang/rust/issues/91611>.
-    fn init(
-        self,
-        scheduler: &Scheduler<Self>,
-    ) -> Pin<Box<dyn Future<Output = InitializedModel<Self>> + Send + '_>> {
-        Box::pin(async move {
-            let _ = scheduler; // suppress the unused argument warning
-            self.into()
-        })
-    }
-}
-
-/// Opaque type containing an initialized model.
-///
-/// A model can be converted to an `InitializedModel` using the `Into`/`From`
-/// traits. The implementation of the simulation guarantees that the
-/// [`Model::init()`] method will never be called on a model after conversion to
-/// an `InitializedModel`.
-#[derive(Debug)]
-pub struct InitializedModel<M: Model>(pub(crate) M);
-
-impl<M: Model> From<M> for InitializedModel<M> {
-    fn from(model: M) -> Self {
-        InitializedModel(model)
-    }
-}

asynchronix/src/model/ports.rs

@@ -1,218 +0,0 @@
-//! Model ports for event and query broadcasting.
-//!
-//! Models typically contain [`Output`] and/or [`Requestor`] ports, exposed as
-//! public member variables. Output ports broadcast events to all connected
-//! input ports, while requestor ports broadcast queries to, and retrieve
-//! replies from, all connected replier ports.
-//!
-//! On the surface, output and requestor ports only differ in that sending a
-//! query from a requestor port also returns an iterator over the replies from
-//! all connected ports. Sending a query is more costly, however, because of the
-//! need to wait until all connected models have processed the query. In
-//! contrast, since events are buffered in the mailbox of the target model,
-//! sending an event is a fire-and-forget operation. For this reason, output
-//! ports should generally be preferred over requestor ports when possible.
-
-use std::fmt;
-use std::sync::{Arc, Mutex};
-
-mod broadcaster;
-mod sender;
-
-use crate::model::{InputFn, Model, ReplierFn};
-use crate::simulation::{Address, EventSlot, EventStream};
-use crate::util::spsc_queue;
-
-use broadcaster::Broadcaster;
-
-use self::sender::{EventSender, EventSlotSender, EventStreamSender, QuerySender};
-
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
-/// Unique identifier for a connection between two ports.
-pub struct LineId(u64);
-
-/// An output port.
-///
-/// `Output` ports can be connected to input ports, i.e. to asynchronous model
-/// methods that return no value. They broadcast events to all connected input
-/// ports.
-pub struct Output<T: Clone + Send + 'static> {
-    broadcaster: Broadcaster<T, ()>,
-    next_line_id: u64,
-}
-
-impl<T: Clone + Send + 'static> Output<T> {
-    /// Creates a new, disconnected `Output` port.
-    pub fn new() -> Self {
-        Self::default()
-    }
-
-    /// Adds a connection to an input port of the model specified by the
-    /// address.
-    ///
-    /// The input port must be an asynchronous method of a model of type `M`
-    /// taking as argument a value of type `T` plus, optionally, a scheduler
-    /// reference.
-    pub fn connect<M, F, S>(&mut self, input: F, address: impl Into<Address<M>>) -> LineId
-    where
-        M: Model,
-        F: for<'a> InputFn<'a, M, T, S> + Copy,
-        S: Send + 'static,
-    {
-        assert!(self.next_line_id != u64::MAX);
-        let line_id = LineId(self.next_line_id);
-        self.next_line_id += 1;
-        let sender = Box::new(EventSender::new(input, address.into().0));
-        self.broadcaster.add(sender, line_id);
-
-        line_id
-    }
-
-    /// Adds a connection to an event stream iterator.
-    pub fn connect_stream(&mut self) -> (EventStream<T>, LineId) {
-        assert!(self.next_line_id != u64::MAX);
-        let line_id = LineId(self.next_line_id);
-        self.next_line_id += 1;
-
-        let (producer, consumer) = spsc_queue::spsc_queue();
-        let sender = Box::new(EventStreamSender::new(producer));
-        let event_stream = EventStream::new(consumer);
-
-        self.broadcaster.add(sender, line_id);
-
-        (event_stream, line_id)
-    }
-
-    /// Adds a connection to an event slot.
-    pub fn connect_slot(&mut self) -> (EventSlot<T>, LineId) {
-        assert!(self.next_line_id != u64::MAX);
-        let line_id = LineId(self.next_line_id);
-        self.next_line_id += 1;
-
-        let slot = Arc::new(Mutex::new(None));
-        let sender = Box::new(EventSlotSender::new(slot.clone()));
-        let event_slot = EventSlot::new(slot);
-
-        self.broadcaster.add(sender, line_id);
-
-        (event_slot, line_id)
-    }
-
-    /// Removes the connection specified by the `LineId` parameter.
-    ///
-    /// It is a logic error to specify a line identifier from another [`Output`]
-    /// or [`Requestor`] instance and may result in the disconnection of an
-    /// arbitrary endpoint.
-    pub fn disconnect(&mut self, line_id: LineId) -> Result<(), LineError> {
-        if self.broadcaster.remove(line_id) {
-            Ok(())
-        } else {
-            Err(LineError {})
-        }
-    }
-
-    /// Removes all connections.
-    pub fn disconnect_all(&mut self) {
-        self.broadcaster.clear();
-    }
-
-    /// Broadcasts an event to all connected input ports.
-    pub async fn send(&mut self, arg: T) {
-        self.broadcaster.broadcast_event(arg).await.unwrap();
-    }
-}
-
-impl<T: Clone + Send + 'static> Default for Output<T> {
-    fn default() -> Self {
-        Self {
-            broadcaster: Broadcaster::default(),
-            next_line_id: 0,
-        }
-    }
-}
-
-impl<T: Clone + Send + 'static> fmt::Debug for Output<T> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Output ({} connected ports)", self.broadcaster.len())
-    }
-}
-
-/// A requestor port.
-///
-/// `Requestor` ports can be connected to replier ports, i.e. to asynchronous
-/// model methods that return a value. They broadcast queries to all connected
-/// replier ports.
-pub struct Requestor<T: Clone + Send + 'static, R: Send + 'static> {
-    broadcaster: Broadcaster<T, R>,
-    next_line_id: u64,
-}
-
-impl<T: Clone + Send + 'static, R: Send + 'static> Requestor<T, R> {
-    /// Creates a new, disconnected `Requestor` port.
-    pub fn new() -> Self {
-        Self::default()
-    }
-
-    /// Adds a connection to a replier port of the model specified by the
-    /// address.
-    ///
-    /// The replier port must be an asynchronous method of a model of type `M`
-    /// returning a value of type `R` and taking as argument a value of type `T`
-    /// plus, optionally, a scheduler reference.
-    pub fn connect<M, F, S>(&mut self, replier: F, address: impl Into<Address<M>>) -> LineId
-    where
-        M: Model,
-        F: for<'a> ReplierFn<'a, M, T, R, S> + Copy,
-        S: Send + 'static,
-    {
-        assert!(self.next_line_id != u64::MAX);
-        let line_id = LineId(self.next_line_id);
-        self.next_line_id += 1;
-        let sender = Box::new(QuerySender::new(replier, address.into().0));
-        self.broadcaster.add(sender, line_id);
-
-        line_id
-    }
-
-    /// Removes the connection specified by the `LineId` parameter.
-    ///
-    /// It is a logic error to specify a line identifier from another [`Output`]
-    /// or [`Requestor`] instance and may result in the disconnection of an
-    /// arbitrary endpoint.
-    pub fn disconnect(&mut self, line_id: LineId) -> Result<(), LineError> {
-        if self.broadcaster.remove(line_id) {
-            Ok(())
-        } else {
-            Err(LineError {})
-        }
-    }
-
-    /// Removes all connections.
-    pub fn disconnect_all(&mut self) {
-        self.broadcaster.clear();
-    }
-
-    /// Broadcasts a query to all connected replier ports.
-    pub async fn send(&mut self, arg: T) -> impl Iterator<Item = R> + '_ {
-        self.broadcaster.broadcast_query(arg).await.unwrap()
-    }
-}
-
-impl<T: Clone + Send + 'static, R: Send + 'static> Default for Requestor<T, R> {
-    fn default() -> Self {
-        Self {
-            broadcaster: Broadcaster::default(),
-            next_line_id: 0,
-        }
-    }
-}
-
-impl<T: Clone + Send + 'static, R: Send + 'static> fmt::Debug for Requestor<T, R> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "Requestor ({} connected ports)", self.broadcaster.len())
-    }
-}
-
-/// Error raised when the specified line cannot be found.
-#[derive(Copy, Clone, Debug)]
-pub struct LineError {}

asynchronix/src/model/ports/broadcaster.rs

@@ -1,743 +0,0 @@
-use std::future::Future;
-use std::mem::ManuallyDrop;
-use std::pin::Pin;
-use std::task::{Context, Poll};
-
-use diatomic_waker::WakeSink;
-use recycle_box::{coerce_box, RecycleBox};
-
-use super::sender::{SendError, Sender};
-use super::LineId;
-use task_set::TaskSet;
-
-mod task_set;
-
-/// An object that can efficiently broadcast messages to several addresses.
-///
-/// This object maintains a list of senders associated to each target address.
-/// When a message is broadcasted, the sender futures are awaited in parallel.
-/// This is somewhat similar to what `FuturesOrdered` in the `futures` crate
-/// does, but with some key differences:
-///
-/// - tasks and future storage are reusable to avoid repeated allocation, so
-///   allocation occurs only after a new sender is added,
-/// - the outputs of all sender futures are returned all at once rather than
-///   with an asynchronous iterator (a.k.a. async stream); the implementation
-///   exploits this behavior by waking the main broadcast future only when all
-///   sender futures have been awaken, which strongly reduces overhead since
-///   waking a sender task does not actually schedule it on the executor.
-pub(super) struct Broadcaster<T: Clone + 'static, R: 'static> {
-    /// The list of senders with their associated line identifier.
-    senders: Vec<(LineId, Box<dyn Sender<T, R>>)>,
-    /// Fields explicitly borrowed by the `BroadcastFuture`.
-    shared: Shared<R>,
-}
-
-impl<T: Clone + 'static> Broadcaster<T, ()> {
-    /// Broadcasts an event to all addresses.
-    pub(super) async fn broadcast_event(&mut self, arg: T) -> Result<(), BroadcastError> {
-        match self.senders.as_mut_slice() {
-            // No sender.
-            [] => Ok(()),
-            // One sender.
-            [sender] => sender.1.send(arg).await.map_err(|_| BroadcastError {}),
-            // Multiple senders.
-            _ => self.broadcast(arg).await,
-        }
-    }
-}
-
-impl<T: Clone + 'static, R> Broadcaster<T, R> {
-    /// Adds a new sender associated to the specified identifier.
-    ///
-    /// # Panics
-    ///
-    /// This method will panic if the total count of senders would reach
-    /// `u32::MAX - 1`.
-    pub(super) fn add(&mut self, sender: Box<dyn Sender<T, R>>, id: LineId) {
-        self.senders.push((id, sender));
-
-        self.shared.futures_env.push(FutureEnv {
-            storage: None,
-            output: None,
-        });
-
-        self.shared.task_set.resize(self.senders.len());
-    }
-
-    /// Removes the first sender with the specified identifier, if any.
-    ///
-    /// Returns `true` if there was indeed a sender associated to the specified
-    /// identifier.
-    pub(super) fn remove(&mut self, id: LineId) -> bool {
-        if let Some(pos) = self.senders.iter().position(|s| s.0 == id) {
-            self.senders.swap_remove(pos);
-            self.shared.futures_env.swap_remove(pos);
-            self.shared.task_set.resize(self.senders.len());
-
-            return true;
-        }
-
-        false
-    }
-
-    /// Removes all senders.
-    pub(super) fn clear(&mut self) {
-        self.senders.clear();
-        self.shared.futures_env.clear();
-        self.shared.task_set.resize(0);
-    }
-
-    /// Returns the number of connected senders.
-    pub(super) fn len(&self) -> usize {
-        self.senders.len()
-    }
-
-    /// Broadcasts a query to all addresses and collect all responses.
-    pub(super) async fn broadcast_query(
-        &mut self,
-        arg: T,
-    ) -> Result<impl Iterator<Item = R> + '_, BroadcastError> {
-        match self.senders.as_mut_slice() {
-            // No sender.
-            [] => {}
-            // One sender.
-            [sender] => {
-                let output = sender.1.send(arg).await.map_err(|_| BroadcastError {})?;
-                self.shared.futures_env[0].output = Some(output);
-            }
-            // Multiple senders.
-            _ => self.broadcast(arg).await?,
-        };
-
-        // At this point all outputs should be available so `unwrap` can be
-        // called on the output of each future.
-        let outputs = self
-            .shared
-            .futures_env
-            .iter_mut()
-            .map(|t| t.output.take().unwrap());
-
-        Ok(outputs)
-    }
-
-    /// Efficiently broadcasts a message or a query to multiple addresses.
-    ///
-    /// This method does not collect the responses from queries.
-    fn broadcast(&mut self, arg: T) -> BroadcastFuture<'_, R> {
-        let futures_count = self.senders.len();
-        let mut futures = recycle_vec(self.shared.storage.take().unwrap_or_default());
-
-        // Broadcast the message and collect all futures.
-        for (i, (sender, futures_env)) in self
-            .senders
-            .iter_mut()
-            .zip(self.shared.futures_env.iter_mut())
-            .enumerate()
-        {
-            let future_cache = futures_env
-                .storage
-                .take()
-                .unwrap_or_else(|| RecycleBox::new(()));
-
-            // Move the argument rather than clone it for the last future.
-            if i + 1 == futures_count {
-                let future: RecycleBox<dyn Future<Output = Result<R, SendError>> + Send + '_> =
-                    coerce_box!(RecycleBox::recycle(future_cache, sender.1.send(arg)));
-
-                futures.push(RecycleBox::into_pin(future));
-                break;
-            }
-
-            let future: RecycleBox<dyn Future<Output = Result<R, SendError>> + Send + '_> = coerce_box!(
-                RecycleBox::recycle(future_cache, sender.1.send(arg.clone()))
-            );
-
-            futures.push(RecycleBox::into_pin(future));
-        }
-
-        // Generate the global future.
-        BroadcastFuture::new(&mut self.shared, futures)
-    }
-}
-
-impl<T: Clone + 'static, R> Default for Broadcaster<T, R> {
-    /// Creates an empty `Broadcaster` object.
-    fn default() -> Self {
-        let wake_sink = WakeSink::new();
-        let wake_src = wake_sink.source();
-
-        Self {
-            senders: Vec::new(),
-            shared: Shared {
-                wake_sink,
-                task_set: TaskSet::new(wake_src),
-                futures_env: Vec::new(),
-                storage: None,
-            },
-        }
-    }
-}
-
-/// Data related to a sender future.
-struct FutureEnv<R> {
-    /// Cached storage for the future.
-    storage: Option<RecycleBox<()>>,
-    /// Output of the associated future.
-    output: Option<R>,
-}
-
-/// A type-erased `Send` future wrapped in a `RecycleBox`.
-type RecycleBoxFuture<'a, R> = RecycleBox<dyn Future<Output = Result<R, SendError>> + Send + 'a>;
-
-/// Fields of `Broadcaster` that are explicitly borrowed by a `BroadcastFuture`.
-struct Shared<R> {
-    /// Thread-safe waker handle.
-    wake_sink: WakeSink,
-    /// Tasks associated to the sender futures.
-    task_set: TaskSet,
-    /// Data related to the sender futures.
-    futures_env: Vec<FutureEnv<R>>,
-    /// Cached storage for the sender futures.
-    ///
-    /// When it exists, the cached storage is always an empty vector but it
-    /// typically has a non-zero capacity. Its purpose is to reuse the
-    /// previously allocated capacity when creating new sender futures.
-    storage: Option<Vec<Pin<RecycleBoxFuture<'static, R>>>>,
-}
-
-/// A future aggregating the outputs of a collection of sender futures.
-///
-/// The idea is to join all sender futures as efficiently as possible, meaning:
-///
-/// - the sender futures are polled simultaneously rather than waiting for their
-///   completion in a sequential manner,
-/// - this future is never woken if it can be proven that at least one of the
-///   individual sender task will still be awaken,
-/// - the storage allocated for the sender futures is always returned to the
-///   `Broadcast` object so it can be reused by the next future,
-/// - the happy path (all futures immediately ready) is very fast.
-pub(super) struct BroadcastFuture<'a, R> {
-    /// Reference to the shared fields of the `Broadcast` object.
-    shared: &'a mut Shared<R>,
-    /// List of all send futures.
-    futures: ManuallyDrop<Vec<Pin<RecycleBoxFuture<'a, R>>>>,
-    /// The total count of futures that have not yet been polled to completion.
-    pending_futures_count: usize,
-    /// State of completion of the future.
-    state: FutureState,
-}
-
-impl<'a, R> BroadcastFuture<'a, R> {
-    /// Creates a new `BroadcastFuture`.
-    fn new(shared: &'a mut Shared<R>, futures: Vec<Pin<RecycleBoxFuture<'a, R>>>) -> Self {
-        let futures_count = futures.len();
-
-        assert!(shared.futures_env.len() == futures_count);
-
-        for futures_env in shared.futures_env.iter_mut() {
-            // Drop the previous output if necessary.
-            futures_env.output.take();
-        }
-
-        BroadcastFuture {
-            shared,
-            futures: ManuallyDrop::new(futures),
-            state: FutureState::Uninit,
-            pending_futures_count: futures_count,
-        }
-    }
-}
-
-impl<'a, R> Drop for BroadcastFuture<'a, R> {
-    fn drop(&mut self) {
-        // Safety: this is safe since `self.futures` is never accessed after it
-        // is moved out.
-        let mut futures = unsafe { ManuallyDrop::take(&mut self.futures) };
-
-        // Recycle the future-containing boxes.
-        for (future, futures_env) in futures.drain(..).zip(self.shared.futures_env.iter_mut()) {
-            futures_env.storage = Some(RecycleBox::vacate_pinned(future));
-        }
-
-        // Recycle the vector that contained the futures.
-        self.shared.storage = Some(recycle_vec(futures));
-    }
-}
-
-impl<'a, R> Future for BroadcastFuture<'a, R> {
-    type Output = Result<(), BroadcastError>;
-
-    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        let this = &mut *self;
-
-        assert_ne!(this.state, FutureState::Completed);
-
-        // Poll all sender futures once if this is the first time the broadcast
-        // future is polled.
-        if this.state == FutureState::Uninit {
-            // Prevent spurious wake-ups.
-            this.shared.task_set.discard_scheduled();
-
-            for task_idx in 0..this.futures.len() {
-                let future_env = &mut this.shared.futures_env[task_idx];
-                let future = &mut this.futures[task_idx];
-                let task_waker_ref = this.shared.task_set.waker_of(task_idx);
-                let task_cx_ref = &mut Context::from_waker(&task_waker_ref);
-
-                match future.as_mut().poll(task_cx_ref) {
-                    Poll::Ready(Ok(output)) => {
-                        future_env.output = Some(output);
-                        this.pending_futures_count -= 1;
-                    }
-                    Poll::Ready(Err(_)) => {
-                        this.state = FutureState::Completed;
-
-                        return Poll::Ready(Err(BroadcastError {}));
-                    }
-                    Poll::Pending => {}
-                }
-            }
-
-            if this.pending_futures_count == 0 {
-                this.state = FutureState::Completed;
-
-                return Poll::Ready(Ok(()));
-            }
-
-            this.state = FutureState::Pending;
-        }
-
-        // Repeatedly poll the futures of all scheduled tasks until there are no
-        // more scheduled tasks.
-        loop {
-            // Only register the waker if it is probable that we won't find any
-            // scheduled task.
-            if !this.shared.task_set.has_scheduled() {
-                this.shared.wake_sink.register(cx.waker());
-            }
-
-            // Retrieve the indices of the scheduled tasks if any. If there are
-            // no scheduled tasks, `Poll::Pending` is returned and this future
-            // will be awaken again when enough tasks have been scheduled.
-            let scheduled_tasks = match this
-                .shared
-                .task_set
-                .steal_scheduled(this.pending_futures_count)
-            {
-                Some(st) => st,
-                None => return Poll::Pending,
-            };
-
-            for task_idx in scheduled_tasks {
-                let future_env = &mut this.shared.futures_env[task_idx];
-
-                // Do not poll completed futures.
-                if future_env.output.is_some() {
-                    continue;
-                }
-
-                let future = &mut this.futures[task_idx];
-                let task_waker_ref = this.shared.task_set.waker_of(task_idx);
-                let task_cx_ref = &mut Context::from_waker(&task_waker_ref);
-
-                match future.as_mut().poll(task_cx_ref) {
-                    Poll::Ready(Ok(output)) => {
-                        future_env.output = Some(output);
-                        this.pending_futures_count -= 1;
-                    }
-                    Poll::Ready(Err(_)) => {
-                        this.state = FutureState::Completed;
-
-                        return Poll::Ready(Err(BroadcastError {}));
-                    }
-                    Poll::Pending => {}
-                }
-            }
-
-            if this.pending_futures_count == 0 {
-                this.state = FutureState::Completed;
-
-                return Poll::Ready(Ok(()));
-            }
-        }
-    }
-}
-
-/// Error returned when a message could not be delivered.
-#[derive(Debug)]
-pub(super) struct BroadcastError {}
-
-#[derive(Debug, PartialEq)]
-enum FutureState {
-    Uninit,
-    Pending,
-    Completed,
-}
-
-/// Drops all items in a vector and returns an empty vector of another type,
-/// preserving the allocation and capacity of the original vector provided that
-/// the layouts of `T` and `U` are compatible.
-///
-/// # Panics
-///
-/// This will panic in debug mode if the layouts are incompatible.
-fn recycle_vec<T, U>(mut v: Vec<T>) -> Vec<U> {
-    debug_assert_eq!(
-        std::alloc::Layout::new::<T>(),
-        std::alloc::Layout::new::<U>()
-    );
-
-    let cap = v.capacity();
-
-    // No unsafe here: this just relies on an optimization in the `collect`
-    // method.
-    v.clear();
-    let v_out: Vec<U> = v.into_iter().map(|_| unreachable!()).collect();
-
-    debug_assert_eq!(v_out.capacity(), cap);
-
-    v_out
-}
-
-#[cfg(all(test, not(asynchronix_loom)))]
-mod tests {
-    use std::sync::atomic::{AtomicUsize, Ordering};
-    use std::thread;
-
-    use futures_executor::block_on;
-
-    use crate::channel::Receiver;
-    use crate::time::Scheduler;
-    use crate::time::{MonotonicTime, TearableAtomicTime};
-    use crate::util::priority_queue::PriorityQueue;
-    use crate::util::sync_cell::SyncCell;
-
-    use super::super::*;
-    use super::*;
-
-    struct Counter {
-        inner: Arc<AtomicUsize>,
-    }
-    impl Counter {
-        fn new(counter: Arc<AtomicUsize>) -> Self {
-            Self { inner: counter }
-        }
-        async fn inc(&mut self, by: usize) {
-            self.inner.fetch_add(by, Ordering::Relaxed);
-        }
-        async fn fetch_inc(&mut self, by: usize) -> usize {
-            let res = self.inner.fetch_add(by, Ordering::Relaxed);
-            res
-        }
-    }
-    impl Model for Counter {}
-
-    #[test]
-    fn broadcast_event_smoke() {
-        const N_RECV: usize = 4;
-
-        let mut mailboxes = Vec::new();
-        let mut broadcaster = Broadcaster::default();
-        for id in 0..N_RECV {
-            let mailbox = Receiver::new(10);
-            let address = mailbox.sender();
-            let sender = Box::new(EventSender::new(Counter::inc, address));
-
-            broadcaster.add(sender, LineId(id as u64));
-            mailboxes.push(mailbox);
-        }
-
-        let th_broadcast = thread::spawn(move || {
-            block_on(broadcaster.broadcast_event(1)).unwrap();
-        });
-
-        let counter = Arc::new(AtomicUsize::new(0));
-
-        let th_recv: Vec<_> = mailboxes
-            .into_iter()
-            .map(|mut mailbox| {
-                thread::spawn({
-                    let mut counter = Counter::new(counter.clone());
-
-                    move || {
-                        let dummy_address = Receiver::new(1).sender();
-                        let dummy_priority_queue = Arc::new(Mutex::new(PriorityQueue::new()));
-                        let dummy_time =
-                            SyncCell::new(TearableAtomicTime::new(MonotonicTime::EPOCH)).reader();
-                        let dummy_scheduler =
-                            Scheduler::new(dummy_address, dummy_priority_queue, dummy_time);
-                        block_on(mailbox.recv(&mut counter, &dummy_scheduler)).unwrap();
-                    }
-                })
-            })
-            .collect();
-
-        th_broadcast.join().unwrap();
-        for th in th_recv {
-            th.join().unwrap();
-        }
-
-        assert_eq!(counter.load(Ordering::Relaxed), N_RECV);
-    }
-
-    #[test]
-    fn broadcast_query_smoke() {
-        const N_RECV: usize = 4;
-
-        let mut mailboxes = Vec::new();
-        let mut broadcaster = Broadcaster::default();
-        for id in 0..N_RECV {
-            let mailbox = Receiver::new(10);
-            let address = mailbox.sender();
-            let sender = Box::new(QuerySender::new(Counter::fetch_inc, address));
-
-            broadcaster.add(sender, LineId(id as u64));
-            mailboxes.push(mailbox);
-        }
-
-        let th_broadcast = thread::spawn(move || {
-            let iter = block_on(broadcaster.broadcast_query(1)).unwrap();
-            let sum = iter.fold(0, |acc, val| acc + val);
-
-            assert_eq!(sum, N_RECV * (N_RECV - 1) / 2); // sum of {0, 1, 2, ..., (N_RECV - 1)}
-        });
-
-        let counter = Arc::new(AtomicUsize::new(0));
-
-        let th_recv: Vec<_> = mailboxes
-            .into_iter()
-            .map(|mut mailbox| {
-                thread::spawn({
-                    let mut counter = Counter::new(counter.clone());
-
-                    move || {
-                        let dummy_address = Receiver::new(1).sender();
-                        let dummy_priority_queue = Arc::new(Mutex::new(PriorityQueue::new()));
-                        let dummy_time =
-                            SyncCell::new(TearableAtomicTime::new(MonotonicTime::EPOCH)).reader();
-                        let dummy_scheduler =
-                            Scheduler::new(dummy_address, dummy_priority_queue, dummy_time);
-                        block_on(mailbox.recv(&mut counter, &dummy_scheduler)).unwrap();
-                        thread::sleep(std::time::Duration::from_millis(100));
-                    }
-                })
-            })
-            .collect();
-
-        th_broadcast.join().unwrap();
-        for th in th_recv {
-            th.join().unwrap();
-        }
-
-        assert_eq!(counter.load(Ordering::Relaxed), N_RECV);
-    }
-}
-
-#[cfg(all(test, asynchronix_loom))]
-mod tests {
-    use futures_channel::mpsc;
-    use futures_util::StreamExt;
-
-    use loom::model::Builder;
-    use loom::sync::atomic::{AtomicBool, Ordering};
-    use loom::thread;
-
-    use waker_fn::waker_fn;
-
-    use super::super::sender::RecycledFuture;
-    use super::*;
-
-    // An event that may be waken spuriously.
-    struct TestEvent<R> {
-        receiver: mpsc::UnboundedReceiver<Option<R>>,
-        fut_storage: Option<RecycleBox<()>>,
-    }
-    impl<R: Send> Sender<(), R> for TestEvent<R> {
-        fn send(&mut self, _arg: ()) -> RecycledFuture<'_, Result<R, SendError>> {
-            let fut_storage = &mut self.fut_storage;
-            let receiver = &mut self.receiver;
-
-            RecycledFuture::new(fut_storage, async {
-                let mut stream = Box::pin(receiver.filter_map(|item| async { item }));
-
-                Ok(stream.next().await.unwrap())
-            })
-        }
-    }
-
-    // An object that can wake a `TestEvent`.
-    #[derive(Clone)]
-    struct TestEventWaker<R> {
-        sender: mpsc::UnboundedSender<Option<R>>,
-    }
-    impl<R> TestEventWaker<R> {
-        fn wake_spurious(&self) {
-            let _ = self.sender.unbounded_send(None);
-        }
-        fn wake_final(&self, value: R) {
-            let _ = self.sender.unbounded_send(Some(value));
-        }
-    }
-
-    fn test_event<R>() -> (TestEvent<R>, TestEventWaker<R>) {
-        let (sender, receiver) = mpsc::unbounded();
-
-        (
-            TestEvent {
-                receiver,
-                fut_storage: None,
-            },
-            TestEventWaker { sender },
-        )
-    }
-
-    #[test]
-    fn loom_broadcast_basic() {
-        const DEFAULT_PREEMPTION_BOUND: usize = 3;
-
-        let mut builder = Builder::new();
-        if builder.preemption_bound.is_none() {
-            builder.preemption_bound = Some(DEFAULT_PREEMPTION_BOUND);
-        }
-
-        builder.check(move || {
-            let (test_event1, waker1) = test_event::<usize>();
-            let (test_event2, waker2) = test_event::<usize>();
-            let (test_event3, waker3) = test_event::<usize>();
-
-            let mut broadcaster = Broadcaster::default();
-            broadcaster.add(Box::new(test_event1), LineId(1));
-            broadcaster.add(Box::new(test_event2), LineId(2));
-            broadcaster.add(Box::new(test_event3), LineId(3));
-
-            let mut fut = Box::pin(broadcaster.broadcast_query(()));
-            let is_scheduled = loom::sync::Arc::new(AtomicBool::new(false));
-            let is_scheduled_waker = is_scheduled.clone();
-
-            let waker = waker_fn(move || {
-                // We use swap rather than a plain store to work around this
-                // bug: <https://github.com/tokio-rs/loom/issues/254>
-                is_scheduled_waker.swap(true, Ordering::Release);
-            });
-            let mut cx = Context::from_waker(&waker);
-
-            let th1 = thread::spawn(move || waker1.wake_final(3));
-            let th2 = thread::spawn(move || waker2.wake_final(7));
-            let th3 = thread::spawn(move || waker3.wake_final(42));
-
-            let mut schedule_count = 0;
-            loop {
-                match fut.as_mut().poll(&mut cx) {
-                    Poll::Ready(Ok(mut res)) => {
-                        assert_eq!(res.next(), Some(3));
-                        assert_eq!(res.next(), Some(7));
-                        assert_eq!(res.next(), Some(42));
-                        assert_eq!(res.next(), None);
-
-                        return;
-                    }
-                    Poll::Ready(Err(_)) => panic!("sender error"),
-                    Poll::Pending => {}
-                }
-
-                // If the task has not been scheduled, exit the polling loop.
-                if !is_scheduled.swap(false, Ordering::Acquire) {
-                    break;
-                }
-                schedule_count += 1;
-                assert!(schedule_count <= 1);
-            }
-
-            th1.join().unwrap();
-            th2.join().unwrap();
-            th3.join().unwrap();
-
-            assert!(is_scheduled.load(Ordering::Acquire));
-
-            match fut.as_mut().poll(&mut cx) {
-                Poll::Ready(Ok(mut res)) => {
-                    assert_eq!(res.next(), Some(3));
-                    assert_eq!(res.next(), Some(7));
-                    assert_eq!(res.next(), Some(42));
-                    assert_eq!(res.next(), None);
-                }
-                Poll::Ready(Err(_)) => panic!("sender error"),
-                Poll::Pending => panic!("the future has not completed"),
-            };
-        });
-    }
-
-    #[test]
-    fn loom_broadcast_spurious() {
-        const DEFAULT_PREEMPTION_BOUND: usize = 3;
-
-        let mut builder = Builder::new();
-        if builder.preemption_bound.is_none() {
-            builder.preemption_bound = Some(DEFAULT_PREEMPTION_BOUND);
-        }
-
-        builder.check(move || {
-            let (test_event1, waker1) = test_event::<usize>();
-            let (test_event2, waker2) = test_event::<usize>();
-
-            let mut broadcaster = Broadcaster::default();
-            broadcaster.add(Box::new(test_event1), LineId(1));
-            broadcaster.add(Box::new(test_event2), LineId(2));
-
-            let mut fut = Box::pin(broadcaster.broadcast_query(()));
-            let is_scheduled = loom::sync::Arc::new(AtomicBool::new(false));
-            let is_scheduled_waker = is_scheduled.clone();
-
-            let waker = waker_fn(move || {
-                // We use swap rather than a plain store to work around this
-                // bug: <https://github.com/tokio-rs/loom/issues/254>
-                is_scheduled_waker.swap(true, Ordering::Release);
-            });
-            let mut cx = Context::from_waker(&waker);
-
-            let spurious_waker = waker1.clone();
-            let th1 = thread::spawn(move || waker1.wake_final(3));
-            let th2 = thread::spawn(move || waker2.wake_final(7));
-            let th_spurious = thread::spawn(move || spurious_waker.wake_spurious());
-
-            let mut schedule_count = 0;
-            loop {
-                match fut.as_mut().poll(&mut cx) {
-                    Poll::Ready(Ok(mut res)) => {
-                        assert_eq!(res.next(), Some(3));
-                        assert_eq!(res.next(), Some(7));
-                        assert_eq!(res.next(), None);
-
-                        return;
-                    }
-                    Poll::Ready(Err(_)) => panic!("sender error"),
-                    Poll::Pending => {}
-                }
-
-                // If the task has not been scheduled, exit the polling loop.
-                if !is_scheduled.swap(false, Ordering::Acquire) {
-                    break;
-                }
-                schedule_count += 1;
-                assert!(schedule_count <= 2);
-            }
-
-            th1.join().unwrap();
-            th2.join().unwrap();
-            th_spurious.join().unwrap();
-
-            assert!(is_scheduled.load(Ordering::Acquire));
-
-            match fut.as_mut().poll(&mut cx) {
-                Poll::Ready(Ok(mut res)) => {
-                    assert_eq!(res.next(), Some(3));
-                    assert_eq!(res.next(), Some(7));
-                    assert_eq!(res.next(), None);
-                }
-                Poll::Ready(Err(_)) => panic!("sender error"),
-                Poll::Pending => panic!("the future has not completed"),
-            };
-        });
-    }
-}

asynchronix/src/model/ports/sender.rs

@@ -1,245 +0,0 @@
-use std::error::Error;
-use std::fmt;
-use std::future::Future;
-use std::marker::PhantomData;
-use std::mem::ManuallyDrop;
-use std::pin::Pin;
-use std::sync::{Arc, Mutex};
-use std::task::{Context, Poll};
-
-use recycle_box::{coerce_box, RecycleBox};
-
-use crate::channel;
-use crate::model::{InputFn, Model, ReplierFn};
-use crate::util::spsc_queue;
-
-/// Abstraction over `EventSender` and `QuerySender`.
-pub(super) trait Sender<T, R>: Send {
-    fn send(&mut self, arg: T) -> RecycledFuture<'_, Result<R, SendError>>;
-}
-
-/// An object that can send a payload to a model.
-pub(super) struct EventSender<M: 'static, F, T, S> {
-    func: F,
-    sender: channel::Sender<M>,
-    fut_storage: Option<RecycleBox<()>>,
-    _phantom_closure: PhantomData<fn(&mut M, T)>,
-    _phantom_closure_marker: PhantomData<S>,
-}
-
-impl<M: Send, F, T, S> EventSender<M, F, T, S>
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S>,
-    T: Send + 'static,
-{
-    pub(super) fn new(func: F, sender: channel::Sender<M>) -> Self {
-        Self {
-            func,
-            sender,
-            fut_storage: None,
-            _phantom_closure: PhantomData,
-            _phantom_closure_marker: PhantomData,
-        }
-    }
-}
-
-impl<M: Send, F, T, S> Sender<T, ()> for EventSender<M, F, T, S>
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S> + Copy,
-    T: Send + 'static,
-    S: Send,
-{
-    fn send(&mut self, arg: T) -> RecycledFuture<'_, Result<(), SendError>> {
-        let func = self.func;
-
-        let fut = self.sender.send(move |model, scheduler, recycle_box| {
-            let fut = func.call(model, arg, scheduler);
-
-            coerce_box!(RecycleBox::recycle(recycle_box, fut))
-        });
-
-        RecycledFuture::new(&mut self.fut_storage, async move {
-            fut.await.map_err(|_| SendError {})
-        })
-    }
-}
-
-/// An object that can send a payload to a model and retrieve a response.
-pub(super) struct QuerySender<M: 'static, F, T, R, S> {
-    func: F,
-    sender: channel::Sender<M>,
-    receiver: multishot::Receiver<R>,
-    fut_storage: Option<RecycleBox<()>>,
-    _phantom_closure: PhantomData<fn(&mut M, T) -> R>,
-    _phantom_closure_marker: PhantomData<S>,
-}
-
-impl<M, F, T, R, S> QuerySender<M, F, T, R, S>
-where
-    M: Model,
-    F: for<'a> ReplierFn<'a, M, T, R, S>,
-    T: Send + 'static,
-    R: Send + 'static,
-{
-    pub(super) fn new(func: F, sender: channel::Sender<M>) -> Self {
-        Self {
-            func,
-            sender,
-            receiver: multishot::Receiver::new(),
-            fut_storage: None,
-            _phantom_closure: PhantomData,
-            _phantom_closure_marker: PhantomData,
-        }
-    }
-}
-
-impl<M, F, T, R, S> Sender<T, R> for QuerySender<M, F, T, R, S>
-where
-    M: Model,
-    F: for<'a> ReplierFn<'a, M, T, R, S> + Copy,
-    T: Send + 'static,
-    R: Send + 'static,
-    S: Send,
-{
-    fn send(&mut self, arg: T) -> RecycledFuture<'_, Result<R, SendError>> {
-        let func = self.func;
-        let sender = &mut self.sender;
-        let reply_receiver = &mut self.receiver;
-        let fut_storage = &mut self.fut_storage;
-
-        // The previous future generated by this method should have been polled
-        // to completion so a new sender should be readily available.
-        let reply_sender = reply_receiver.sender().unwrap();
-
-        let send_fut = sender.send(move |model, scheduler, recycle_box| {
-            let fut = async move {
-                let reply = func.call(model, arg, scheduler).await;
-                reply_sender.send(reply);
-            };
-
-            coerce_box!(RecycleBox::recycle(recycle_box, fut))
-        });
-
-        RecycledFuture::new(fut_storage, async move {
-            // Send the message.
-            send_fut.await.map_err(|_| SendError {})?;
-
-            // Wait until the message is processed and the reply is sent back.
-            // If an error is received, it most likely means the mailbox was
-            // dropped before the message was processed.
-            reply_receiver.recv().await.map_err(|_| SendError {})
-        })
-    }
-}
-
-/// An object that can send a payload to an unbounded queue.
-pub(super) struct EventStreamSender<T> {
-    producer: spsc_queue::Producer<T>,
-    fut_storage: Option<RecycleBox<()>>,
-}
-
-impl<T> EventStreamSender<T> {
-    pub(super) fn new(producer: spsc_queue::Producer<T>) -> Self {
-        Self {
-            producer,
-            fut_storage: None,
-        }
-    }
-}
-
-impl<T> Sender<T, ()> for EventStreamSender<T>
-where
-    T: Send + 'static,
-{
-    fn send(&mut self, arg: T) -> RecycledFuture<'_, Result<(), SendError>> {
-        let producer = &mut self.producer;
-
-        RecycledFuture::new(&mut self.fut_storage, async move {
-            producer.push(arg).map_err(|_| SendError {})
-        })
-    }
-}
-
-/// An object that can send a payload to a mutex-protected slot.
-pub(super) struct EventSlotSender<T> {
-    slot: Arc<Mutex<Option<T>>>,
-    fut_storage: Option<RecycleBox<()>>,
-}
-
-impl<T> EventSlotSender<T> {
-    pub(super) fn new(slot: Arc<Mutex<Option<T>>>) -> Self {
-        Self {
-            slot,
-            fut_storage: None,
-        }
-    }
-}
-
-impl<T> Sender<T, ()> for EventSlotSender<T>
-where
-    T: Send + 'static,
-{
-    fn send(&mut self, arg: T) -> RecycledFuture<'_, Result<(), SendError>> {
-        let slot = &*self.slot;
-
-        RecycledFuture::new(&mut self.fut_storage, async move {
-            let mut slot = slot.lock().unwrap();
-            *slot = Some(arg);
-
-            Ok(())
-        })
-    }
-}
-
-#[derive(Debug, PartialEq, Eq, Clone, Copy)]
-/// Error returned when the mailbox was closed or dropped.
-pub(super) struct SendError {}
-
-impl fmt::Display for SendError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "sending message into a closed mailbox")
-    }
-}
-
-impl Error for SendError {}
-
-pub(super) struct RecycledFuture<'a, T> {
-    fut: ManuallyDrop<Pin<RecycleBox<dyn Future<Output = T> + Send + 'a>>>,
-    lender_box: &'a mut Option<RecycleBox<()>>,
-}
-impl<'a, T> RecycledFuture<'a, T> {
-    pub(super) fn new<F: Future<Output = T> + Send + 'a>(
-        lender_box: &'a mut Option<RecycleBox<()>>,
-        fut: F,
-    ) -> Self {
-        let vacated_box = lender_box.take().unwrap_or_else(|| RecycleBox::new(()));
-        let fut: RecycleBox<dyn Future<Output = T> + Send + 'a> =
-            coerce_box!(RecycleBox::recycle(vacated_box, fut));
-
-        Self {
-            fut: ManuallyDrop::new(RecycleBox::into_pin(fut)),
-            lender_box,
-        }
-    }
-}
-
-impl<'a, T> Drop for RecycledFuture<'a, T> {
-    fn drop(&mut self) {
-        // Return the box to the lender.
-        //
-        // Safety: taking the `fut` member is safe since it is never used again.
-        *self.lender_box = Some(RecycleBox::vacate_pinned(unsafe {
-            ManuallyDrop::take(&mut self.fut)
-        }));
-    }
-}
-
-impl<'a, T> Future for RecycledFuture<'a, T> {
-    type Output = T;
-
-    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        self.fut.as_mut().poll(cx)
-    }
-}

asynchronix/src/simulation.rs

@@ -1,635 +0,0 @@
-//! Discrete-event simulation management.
-//!
-//! This module contains most notably the [`Simulation`] environment, the
-//! [`SimInit`] simulation builder, the [`Mailbox`] and [`Address`] types as
-//! well as miscellaneous other types related to simulation management.
-//!
-//! # Simulation lifecycle
-//!
-//! The lifecycle of a simulation bench typically comprises the following
-//! stages:
-//!
-//! 1. instantiation of models and their [`Mailbox`]es,
-//! 2. connection of the models' output/requestor ports to input/replier ports
-//!    using the [`Address`]es of the target models,
-//! 3. instantiation of a [`SimInit`] simulation builder and migration of all
-//!    models and mailboxes to the builder with [`SimInit::add_model()`],
-//! 4. initialization of a [`Simulation`] instance with [`SimInit::init()`] or
-//!    [`SimInit::init_with_clock()`],
-//! 5. discrete-time simulation, which typically involves scheduling events and
-//!    incrementing simulation time while observing the models outputs.
-//!
-//! Most information necessary to run a simulation is available in the root
-//! crate [documentation](crate) and in the [`SimInit`] and [`Simulation`]
-//! documentation. The next section complement this information with a set of
-//! practical recommendations that can help run and troubleshoot simulations.
-//!
-//! # Practical considerations
-//!
-//! ## Mailbox capacity
-//!
-//! A [`Mailbox`] is a buffer that store incoming events and queries for a
-//! single model instance. Mailboxes have a bounded capacity, which defaults to
-//! [`Mailbox::DEFAULT_CAPACITY`].
-//!
-//! The capacity is a trade-off: too large a capacity may lead to excessive
-//! memory usage, whereas too small a capacity can hamper performance and
-//! increase the likelihood of deadlocks (see next section). Note that, because
-//! a mailbox may receive events or queries of various sizes, it is actually the
-//! largest message sent that ultimately determines the amount of allocated
-//! memory.
-//!
-//! The default capacity should prove a reasonable trade-off in most cases, but
-//! for situations where it is not appropriate, it is possible to instantiate
-//! mailboxes with a custom capacity by using [`Mailbox::with_capacity()`]
-//! instead of [`Mailbox::new()`].
-//!
-//! ## Avoiding deadlocks
-//!
-//! While the underlying architecture of Asynchronix—the actor model—should
-//! prevent most race conditions (including obviously data races which are not
-//! possible in safe Rust) it is still possible in theory to generate deadlocks.
-//! Though rare in practice, these may occur due to one of the below:
-//!
-//! 1. *query loopback*: if a model sends a query which is further forwarded by
-//!    other models until it loops back to the initial model, that model would
-//!    in effect wait for its own response and block,
-//! 2. *mailbox saturation*: if several models concurrently send to one another
-//!    a very large number of messages in succession, these models may end up
-//!    saturating all mailboxes, at which point they will wait for the other's
-//!    mailboxes to free space so they can send the next message, eventually
-//!    preventing all of them to make further progress.
-//!
-//! The first scenario is usually very easy to avoid and is typically the result
-//! of an improper assembly of models. Because requestor ports are only used
-//! sparingly in idiomatic simulations, this situation should be relatively
-//! exceptional.
-//!
-//! The second scenario is rare in well-behaving models and if it occurs, it is
-//! most typically at the very beginning of a simulation when all models
-//! simultaneously send events during the call to
-//! [`Model::init()`](crate::model::Model::init). If such a large amount of
-//! concurrent messages is deemed normal behavior, the issue can be readily
-//! remedied by increasing the capacity of the saturated mailboxes.
-//!
-//! At the moment, Asynchronix is unfortunately not able to discriminate between
-//! such pathological deadlocks and the "expected" deadlock that occurs when all
-//! events in a given time slice have completed and all models are starved on an
-//! empty mailbox. Consequently, blocking method such as [`SimInit::init()`],
-//! [`Simulation::step()`], [`Simulation::send_event()`], etc., will return
-//! without error after a pathological deadlock, leaving the user responsible
-//! for inferring the deadlock from the behavior of the simulation in the next
-//! steps. This is obviously not ideal, but is hopefully only a temporary state
-//! of things until a more precise deadlock detection algorithm is implemented.
-//!
-//! ## Modifying connections during simulation
-//!
-//! Although uncommon, there is sometimes a need for connecting and/or
-//! disconnecting models after they have been migrated to the simulation.
-//! Likewise, one may want to connect or disconnect an [`EventSlot`] or
-//! [`EventStream`] after the simulation has been instantiated.
-//!
-//! There is actually a very simple solution to this problem: since the
-//! [`InputFn`](crate::model::InputFn) trait also matches closures of type
-//! `FnOnce(&mut impl Model)`, it is enough to invoke
-//! [`Simulation::send_event()`] with a closure that connects or disconnects a
-//! port, such as:
-//!
-//! ```
-//! # use asynchronix::model::{Model, Output};
-//! # use asynchronix::time::{MonotonicTime, Scheduler};
-//! # use asynchronix::simulation::{Mailbox, SimInit};
-//! # pub struct ModelA {
-//! #     pub output: Output<i32>,
-//! # }
-//! # impl Model for ModelA {};
-//! # pub struct ModelB {}
-//! # impl ModelB {
-//! #     pub fn input(&mut self, value: i32) {}
-//! # }
-//! # impl Model for ModelB {};
-//! # let modelA_addr = Mailbox::<ModelA>::new().address();
-//! # let modelB_addr = Mailbox::<ModelB>::new().address();
-//! # let mut simu = SimInit::new().init(MonotonicTime::EPOCH);
-//! simu.send_event(
-//!     |m: &mut ModelA| {
-//!         m.output.connect(ModelB::input, modelB_addr);
-//!     },
-//!     (),
-//!     &modelA_addr
-//! );
-//! ```
-mod endpoints;
-mod mailbox;
-mod sim_init;
-
-pub use endpoints::{EventSlot, EventStream};
-pub use mailbox::{Address, Mailbox};
-pub use sim_init::SimInit;
-
-use std::error::Error;
-use std::fmt;
-use std::future::Future;
-use std::sync::{Arc, Mutex, MutexGuard};
-use std::time::Duration;
-
-use recycle_box::{coerce_box, RecycleBox};
-
-use crate::executor::Executor;
-use crate::model::{InputFn, Model, ReplierFn};
-use crate::time::{
-    self, Clock, Deadline, EventKey, MonotonicTime, NoClock, ScheduledEvent, SchedulerQueue,
-    SchedulingError, TearableAtomicTime,
-};
-use crate::util::futures::SeqFuture;
-use crate::util::slot;
-use crate::util::sync_cell::SyncCell;
-
-/// Simulation environment.
-///
-/// A `Simulation` is created by calling
-/// [`SimInit::init()`](crate::simulation::SimInit::init) or
-/// [`SimInit::init_with_clock()`](crate::simulation::SimInit::init_with_clock)
-/// method on a simulation initializer. It contains an asynchronous executor
-/// that runs all simulation models added beforehand to
-/// [`SimInit`](crate::simulation::SimInit).
-///
-/// A [`Simulation`] object also manages an event scheduling queue and
-/// simulation time. The scheduling queue can be accessed from the simulation
-/// itself, but also from models via the optional
-/// [`&Scheduler`](time::Scheduler) argument of input and replier port methods.
-/// Likewise, simulation time can be accessed with the [`Simulation::time()`]
-/// method, or from models with the [`Scheduler::time()`](time::Scheduler::time)
-/// method.
-///
-/// Events and queries can be scheduled immediately, *i.e.* for the current
-/// simulation time, using [`send_event()`](Simulation::send_event) and
-/// [`send_query()`](Simulation::send_query). Calling these methods will block
-/// until all computations triggered by such event or query have completed. In
-/// the case of queries, the response is returned.
-///
-/// Events can also be scheduled at a future simulation time using one of the
-/// [`schedule_*()`](Simulation::schedule_event) method. These methods queue an
-/// event without blocking.
-///
-/// Finally, the [`Simulation`] instance manages simulation time. A call to
-/// [`step()`](Simulation::step) will:
-///
-/// 1. increment simulation time until that of the next scheduled event in
-///    chronological order, then
-/// 2. call [`Clock::synchronize()`](time::Clock::synchronize) which, unless the
-///    simulation is configured to run as fast as possible, blocks until the
-///    desired wall clock time, and finally
-/// 3. run all computations scheduled for the new simulation time.
-///
-/// The [`step_by()`](Simulation::step_by) and
-/// [`step_until()`](Simulation::step_until) methods operate similarly but
-/// iterate until the target simulation time has been reached.
-pub struct Simulation {
-    executor: Executor,
-    scheduler_queue: Arc<Mutex<SchedulerQueue>>,
-    time: SyncCell<TearableAtomicTime>,
-    clock: Box<dyn Clock>,
-}
-
-impl Simulation {
-    /// Creates a new `Simulation`.
-    pub(crate) fn new(
-        executor: Executor,
-        scheduler_queue: Arc<Mutex<SchedulerQueue>>,
-        time: SyncCell<TearableAtomicTime>,
-    ) -> Self {
-        Self {
-            executor,
-            scheduler_queue,
-            time,
-            clock: Box::new(NoClock::new()),
-        }
-    }
-
-    /// Creates a new `Simulation` with the specified clock.
-    pub(crate) fn with_clock(
-        executor: Executor,
-        scheduler_queue: Arc<Mutex<SchedulerQueue>>,
-        time: SyncCell<TearableAtomicTime>,
-        clock: impl Clock + 'static,
-    ) -> Self {
-        Self {
-            executor,
-            scheduler_queue,
-            time,
-            clock: Box::new(clock),
-        }
-    }
-
-    /// Returns the current simulation time.
-    pub fn time(&self) -> MonotonicTime {
-        self.time.read()
-    }
-
-    /// Advances simulation time to that of the next scheduled event, processing
-    /// that event as well as all other event scheduled for the same time.
-    ///
-    /// Processing is gated by a (possibly blocking) call to
-    /// [`Clock::synchronize()`](time::Clock::synchronize) on the configured
-    /// simulation clock. This method blocks until all newly processed events
-    /// have completed.
-    pub fn step(&mut self) {
-        self.step_to_next_bounded(MonotonicTime::MAX);
-    }
-
-    /// Iteratively advances the simulation time by the specified duration, as
-    /// if by calling [`Simulation::step()`] repeatedly.
-    ///
-    /// This method blocks until all events scheduled up to the specified target
-    /// time have completed. The simulation time upon completion is equal to the
-    /// initial simulation time incremented by the specified duration, whether
-    /// or not an event was scheduled for that time.
-    pub fn step_by(&mut self, duration: Duration) {
-        let target_time = self.time.read() + duration;
-
-        self.step_until_unchecked(target_time);
-    }
-
-    /// Iteratively advances the simulation time until the specified deadline,
-    /// as if by calling [`Simulation::step()`] repeatedly.
-    ///
-    /// This method blocks until all events scheduled up to the specified target
-    /// time have completed. The simulation time upon completion is equal to the
-    /// specified target time, whether or not an event was scheduled for that
-    /// time.
-    pub fn step_until(&mut self, target_time: MonotonicTime) -> Result<(), SchedulingError> {
-        if self.time.read() >= target_time {
-            return Err(SchedulingError::InvalidScheduledTime);
-        }
-        self.step_until_unchecked(target_time);
-
-        Ok(())
-    }
-
-    /// Schedules an event at a future time.
-    ///
-    /// An error is returned if the specified time is not in the future of the
-    /// current simulation time.
-    ///
-    /// Events scheduled for the same time and targeting the same model are
-    /// guaranteed to be processed according to the scheduling order.
-    ///
-    /// See also: [`time::Scheduler::schedule_event`].
-    pub fn schedule_event<M, F, T, S>(
-        &mut self,
-        deadline: impl Deadline,
-        func: F,
-        arg: T,
-        address: impl Into<Address<M>>,
-    ) -> Result<(), SchedulingError>
-    where
-        M: Model,
-        F: for<'a> InputFn<'a, M, T, S>,
-        T: Send + Clone + 'static,
-        S: Send + 'static,
-    {
-        let now = self.time();
-        let time = deadline.into_time(now);
-        if now >= time {
-            return Err(SchedulingError::InvalidScheduledTime);
-        }
-        time::schedule_event_at_unchecked(time, func, arg, address.into().0, &self.scheduler_queue);
-
-        Ok(())
-    }
-
-    /// Schedules a cancellable event at a future time and returns an event key.
-    ///
-    /// An error is returned if the specified time is not in the future of the
-    /// current simulation time.
-    ///
-    /// Events scheduled for the same time and targeting the same model are
-    /// guaranteed to be processed according to the scheduling order.
-    ///
-    /// See also: [`time::Scheduler::schedule_keyed_event`].
-    pub fn schedule_keyed_event<M, F, T, S>(
-        &mut self,
-        deadline: impl Deadline,
-        func: F,
-        arg: T,
-        address: impl Into<Address<M>>,
-    ) -> Result<EventKey, SchedulingError>
-    where
-        M: Model,
-        F: for<'a> InputFn<'a, M, T, S>,
-        T: Send + Clone + 'static,
-        S: Send + 'static,
-    {
-        let now = self.time();
-        let time = deadline.into_time(now);
-        if now >= time {
-            return Err(SchedulingError::InvalidScheduledTime);
-        }
-        let event_key = time::schedule_keyed_event_at_unchecked(
-            time,
-            func,
-            arg,
-            address.into().0,
-            &self.scheduler_queue,
-        );
-
-        Ok(event_key)
-    }
-
-    /// Schedules a periodically recurring event at a future time.
-    ///
-    /// An error is returned if the specified time is not in the future of the
-    /// current simulation time or if the specified period is null.
-    ///
-    /// Events scheduled for the same time and targeting the same model are
-    /// guaranteed to be processed according to the scheduling order.
-    ///
-    /// See also: [`time::Scheduler::schedule_periodic_event`].
-    pub fn schedule_periodic_event<M, F, T, S>(
-        &mut self,
-        deadline: impl Deadline,
-        period: Duration,
-        func: F,
-        arg: T,
-        address: impl Into<Address<M>>,
-    ) -> Result<(), SchedulingError>
-    where
-        M: Model,
-        F: for<'a> InputFn<'a, M, T, S> + Clone,
-        T: Send + Clone + 'static,
-        S: Send + 'static,
-    {
-        let now = self.time();
-        let time = deadline.into_time(now);
-        if now >= time {
-            return Err(SchedulingError::InvalidScheduledTime);
-        }
-        if period.is_zero() {
-            return Err(SchedulingError::NullRepetitionPeriod);
-        }
-        time::schedule_periodic_event_at_unchecked(
-            time,
-            period,
-            func,
-            arg,
-            address.into().0,
-            &self.scheduler_queue,
-        );
-
-        Ok(())
-    }
-
-    /// Schedules a cancellable, periodically recurring event at a future time
-    /// and returns an event key.
-    ///
-    /// An error is returned if the specified time is not in the future of the
-    /// current simulation time or if the specified period is null.
-    ///
-    /// Events scheduled for the same time and targeting the same model are
-    /// guaranteed to be processed according to the scheduling order.
-    ///
-    /// See also: [`time::Scheduler::schedule_keyed_periodic_event`].
-    pub fn schedule_keyed_periodic_event<M, F, T, S>(
-        &mut self,
-        deadline: impl Deadline,
-        period: Duration,
-        func: F,
-        arg: T,
-        address: impl Into<Address<M>>,
-    ) -> Result<EventKey, SchedulingError>
-    where
-        M: Model,
-        F: for<'a> InputFn<'a, M, T, S> + Clone,
-        T: Send + Clone + 'static,
-        S: Send + 'static,
-    {
-        let now = self.time();
-        let time = deadline.into_time(now);
-        if now >= time {
-            return Err(SchedulingError::InvalidScheduledTime);
-        }
-        if period.is_zero() {
-            return Err(SchedulingError::NullRepetitionPeriod);
-        }
-        let event_key = time::schedule_periodic_keyed_event_at_unchecked(
-            time,
-            period,
-            func,
-            arg,
-            address.into().0,
-            &self.scheduler_queue,
-        );
-
-        Ok(event_key)
-    }
-
-    /// Sends and processes an event, blocking until completion.
-    ///
-    /// Simulation time remains unchanged.
-    pub fn send_event<M, F, T, S>(&mut self, func: F, arg: T, address: impl Into<Address<M>>)
-    where
-        M: Model,
-        F: for<'a> InputFn<'a, M, T, S>,
-        T: Send + Clone + 'static,
-    {
-        let sender = address.into().0;
-        let fut = async move {
-            // Ignore send errors.
-            let _ = sender
-                .send(
-                    move |model: &mut M,
-                          scheduler,
-                          recycle_box: RecycleBox<()>|
-                          -> RecycleBox<dyn Future<Output = ()> + Send + '_> {
-                        let fut = func.call(model, arg, scheduler);
-
-                        coerce_box!(RecycleBox::recycle(recycle_box, fut))
-                    },
-                )
-                .await;
-        };
-
-        self.executor.spawn_and_forget(fut);
-        self.executor.run();
-    }
-
-    /// Sends and processes a query, blocking until completion.
-    ///
-    /// Simulation time remains unchanged.
-    pub fn send_query<M, F, T, R, S>(
-        &mut self,
-        func: F,
-        arg: T,
-        address: impl Into<Address<M>>,
-    ) -> Result<R, QueryError>
-    where
-        M: Model,
-        F: for<'a> ReplierFn<'a, M, T, R, S>,
-        T: Send + Clone + 'static,
-        R: Send + 'static,
-    {
-        let (reply_writer, mut reply_reader) = slot::slot();
-        let sender = address.into().0;
-
-        let fut = async move {
-            // Ignore send errors.
-            let _ = sender
-                .send(
-                    move |model: &mut M,
-                          scheduler,
-                          recycle_box: RecycleBox<()>|
-                          -> RecycleBox<dyn Future<Output = ()> + Send + '_> {
-                        let fut = async move {
-                            let reply = func.call(model, arg, scheduler).await;
-                            let _ = reply_writer.write(reply);
-                        };
-
-                        coerce_box!(RecycleBox::recycle(recycle_box, fut))
-                    },
-                )
-                .await;
-        };
-
-        self.executor.spawn_and_forget(fut);
-        self.executor.run();
-
-        reply_reader.try_read().map_err(|_| QueryError {})
-    }
-
-    /// Advances simulation time to that of the next scheduled event if its
-    /// scheduling time does not exceed the specified bound, processing that
-    /// event as well as all other events scheduled for the same time.
-    ///
-    /// If at least one event was found that satisfied the time bound, the
-    /// corresponding new simulation time is returned.
-    fn step_to_next_bounded(&mut self, upper_time_bound: MonotonicTime) -> Option<MonotonicTime> {
-        // Function pulling the next event. If the event is periodic, it is
-        // immediately re-scheduled.
-        fn pull_next_event(
-            scheduler_queue: &mut MutexGuard<SchedulerQueue>,
-        ) -> Box<dyn ScheduledEvent> {
-            let ((time, channel_id), event) = scheduler_queue.pull().unwrap();
-            if let Some((event_clone, period)) = event.next() {
-                scheduler_queue.insert((time + period, channel_id), event_clone);
-            }
-
-            event
-        }
-
-        // Closure returning the next key which time stamp is no older than the
-        // upper bound, if any. Cancelled events are pulled and discarded.
-        let peek_next_key = |scheduler_queue: &mut MutexGuard<SchedulerQueue>| {
-            loop {
-                match scheduler_queue.peek() {
-                    Some((&k, t)) if k.0 <= upper_time_bound => {
-                        if !t.is_cancelled() {
-                            break Some(k);
-                        }
-                        // Discard cancelled events.
-                        scheduler_queue.pull();
-                    }
-                    _ => break None,
-                }
-            }
-        };
-
-        // Move to the next scheduled time.
-        let mut scheduler_queue = self.scheduler_queue.lock().unwrap();
-        let mut current_key = peek_next_key(&mut scheduler_queue)?;
-        self.time.write(current_key.0);
-
-        loop {
-            let event = pull_next_event(&mut scheduler_queue);
-            let mut next_key = peek_next_key(&mut scheduler_queue);
-            if next_key != Some(current_key) {
-                // Since there are no other events targeting the same mailbox
-                // and the same time, the event is spawned immediately.
-                event.spawn_and_forget(&self.executor);
-            } else {
-                // To ensure that their relative order of execution is
-                // preserved, all event targeting the same mailbox are executed
-                // sequentially within a single compound future.
-                let mut event_sequence = SeqFuture::new();
-                event_sequence.push(event.into_future());
-                loop {
-                    let event = pull_next_event(&mut scheduler_queue);
-                    event_sequence.push(event.into_future());
-                    next_key = peek_next_key(&mut scheduler_queue);
-                    if next_key != Some(current_key) {
-                        break;
-                    }
-                }
-
-                // Spawn a compound future that sequentially polls all events
-                // targeting the same mailbox.
-                self.executor.spawn_and_forget(event_sequence);
-            }
-
-            current_key = match next_key {
-                // If the next event is scheduled at the same time, update the
-                // key and continue.
-                Some(k) if k.0 == current_key.0 => k,
-                // Otherwise wait until all events have completed and return.
-                _ => {
-                    drop(scheduler_queue); // make sure the queue's mutex is released.
-                    let current_time = current_key.0;
-                    // TODO: check synchronization status?
-                    self.clock.synchronize(current_time);
-                    self.executor.run();
-
-                    return Some(current_time);
-                }
-            };
-        }
-    }
-
-    /// Iteratively advances simulation time and processes all events scheduled
-    /// up to the specified target time.
-    ///
-    /// Once the method returns it is guaranteed that (i) all events scheduled
-    /// up to the specified target time have completed and (ii) the final
-    /// simulation time matches the target time.
-    ///
-    /// This method does not check whether the specified time lies in the future
-    /// of the current simulation time.
-    fn step_until_unchecked(&mut self, target_time: MonotonicTime) {
-        loop {
-            match self.step_to_next_bounded(target_time) {
-                // The target time was reached exactly.
-                Some(t) if t == target_time => return,
-                // No events are scheduled before or at the target time.
-                None => {
-                    // Update the simulation time.
-                    self.time.write(target_time);
-                    return;
-                }
-                // The target time was not reached yet.
-                _ => {}
-            }
-        }
-    }
-}
-
-impl fmt::Debug for Simulation {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Simulation")
-            .field("time", &self.time.read())
-            .finish_non_exhaustive()
-    }
-}
-
-/// Error returned when a query did not obtain a response.
-///
-/// This can happen either because the model targeted by the address was not
-/// added to the simulation or due to a simulation deadlock.
-#[derive(Debug, PartialEq, Eq, Clone, Copy)]
-pub struct QueryError {}
-
-impl fmt::Display for QueryError {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(fmt, "the query did not receive a response")
-    }
-}
-
-impl Error for QueryError {}

asynchronix/src/simulation/endpoints.rs

@@ -1,69 +0,0 @@
-use std::fmt;
-use std::sync::{Arc, Mutex, TryLockError, TryLockResult};
-
-use crate::util::spsc_queue;
-
-/// An iterator that returns all events that were broadcast by an output port.
-///
-/// Events are returned in first-in-first-out order. Note that even if the
-/// iterator returns `None`, it may still produce more items after simulation
-/// time is incremented.
-pub struct EventStream<T> {
-    consumer: spsc_queue::Consumer<T>,
-}
-
-impl<T> EventStream<T> {
-    /// Creates a new `EventStream`.
-    pub(crate) fn new(consumer: spsc_queue::Consumer<T>) -> Self {
-        Self { consumer }
-    }
-}
-
-impl<T> Iterator for EventStream<T> {
-    type Item = T;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.consumer.pop()
-    }
-}
-
-impl<T> fmt::Debug for EventStream<T> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        f.debug_struct("EventStream").finish_non_exhaustive()
-    }
-}
-
-/// A single-value slot that holds the last event that was broadcast by an
-/// output port.
-pub struct EventSlot<T> {
-    slot: Arc<Mutex<Option<T>>>,
-}
-
-impl<T> EventSlot<T> {
-    /// Creates a new `EventSlot`.
-    pub(crate) fn new(slot: Arc<Mutex<Option<T>>>) -> Self {
-        Self { slot }
-    }
-
-    /// Take the last event, if any, leaving the slot empty.
-    ///
-    /// Note that even after the event is taken, it may become populated anew
-    /// after simulation time is incremented.
-    pub fn take(&mut self) -> Option<T> {
-        // We don't actually need to take self by mutable reference, but this
-        // signature is probably less surprising for the user and more
-        // consistent with `EventStream`. It also prevents multi-threaded
-        // access, which would be likely to be misused.
-        match self.slot.try_lock() {
-            TryLockResult::Ok(mut v) => v.take(),
-            TryLockResult::Err(TryLockError::WouldBlock) => None,
-            TryLockResult::Err(TryLockError::Poisoned(_)) => panic!(),
-        }
-    }
-}
-
-impl<T> fmt::Debug for EventSlot<T> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        f.debug_struct("EventSlot").finish_non_exhaustive()
-    }
-}

asynchronix/src/simulation/sim_init.rs

@@ -1,100 +0,0 @@
-use std::fmt;
-use std::sync::{Arc, Mutex};
-
-use crate::executor::Executor;
-use crate::model::Model;
-use crate::time::{Clock, Scheduler};
-use crate::time::{MonotonicTime, SchedulerQueue, TearableAtomicTime};
-use crate::util::priority_queue::PriorityQueue;
-use crate::util::sync_cell::SyncCell;
-
-use super::{Mailbox, Simulation};
-
-/// Builder for a multi-threaded, discrete-event simulation.
-pub struct SimInit {
-    executor: Executor,
-    scheduler_queue: Arc<Mutex<SchedulerQueue>>,
-    time: SyncCell<TearableAtomicTime>,
-}
-
-impl SimInit {
-    /// Creates a builder for a multithreaded simulation running on all
-    /// available logical threads.
-    pub fn new() -> Self {
-        Self::with_num_threads(num_cpus::get())
-    }
-
-    /// Creates a builder for a multithreaded simulation running on the
-    /// specified number of threads.
-    pub fn with_num_threads(num_threads: usize) -> Self {
-        // The current executor's implementation caps the number of thread to 64
-        // on 64-bit systems and 32 on 32-bit systems.
-        let num_threads = num_threads.min(usize::BITS as usize);
-
-        Self {
-            executor: Executor::new(num_threads),
-            scheduler_queue: Arc::new(Mutex::new(PriorityQueue::new())),
-            time: SyncCell::new(TearableAtomicTime::new(MonotonicTime::EPOCH)),
-        }
-    }
-
-    /// Adds a model and its mailbox to the simulation bench.
-    pub fn add_model<M: Model>(self, model: M, mailbox: Mailbox<M>) -> Self {
-        let scheduler_queue = self.scheduler_queue.clone();
-        let time = self.time.reader();
-        let mut receiver = mailbox.0;
-
-        self.executor.spawn_and_forget(async move {
-            let sender = receiver.sender();
-            let scheduler = Scheduler::new(sender, scheduler_queue, time);
-            let mut model = model.init(&scheduler).await.0;
-
-            while receiver.recv(&mut model, &scheduler).await.is_ok() {}
-        });
-
-        self
-    }
-
-    /// Builds a simulation initialized at the specified simulation time,
-    /// executing the [`Model::init()`](crate::model::Model::init) method on all
-    /// model initializers.
-    ///
-    /// This is equivalent to calling [`SimInit::init_with_clock()`] with a
-    /// [`NoClock`](crate::time::NoClock) argument and effectively makes the
-    /// simulation run as fast as possible.
-    pub fn init(mut self, start_time: MonotonicTime) -> Simulation {
-        self.time.write(start_time);
-        self.executor.run();
-
-        Simulation::new(self.executor, self.scheduler_queue, self.time)
-    }
-
-    /// Builds a simulation synchronized with the provided
-    /// [`Clock`](crate::time::Clock) and initialized at the specified
-    /// simulation time, executing the
-    /// [`Model::init()`](crate::model::Model::init) method on all model
-    /// initializers.
-    pub fn init_with_clock(
-        mut self,
-        start_time: MonotonicTime,
-        mut clock: impl Clock + 'static,
-    ) -> Simulation {
-        self.time.write(start_time);
-        clock.synchronize(start_time);
-        self.executor.run();
-
-        Simulation::with_clock(self.executor, self.scheduler_queue, self.time, clock)
-    }
-}
-
-impl Default for SimInit {
-    fn default() -> Self {
-        Self::new()
-    }
-}
-
-impl fmt::Debug for SimInit {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("SimInit").finish_non_exhaustive()
-    }
-}

asynchronix/src/time.rs

@@ -1,62 +0,0 @@
-//! Simulation time and scheduling.
-//!
-//! This module provides most notably:
-//!
-//! * [`MonotonicTime`]: a monotonic timestamp based on the [TAI] time standard,
-//! * [`Clock`]: a trait for types that can synchronize a simulation,
-//!       implemented for instance by [`SystemClock`] and [`AutoSystemClock`],
-//! * [`Scheduler`]: a model-local handle to the global scheduler that can be
-//!   used by models to schedule future actions onto themselves.
-//!
-//! [TAI]: https://en.wikipedia.org/wiki/International_Atomic_Time
-//!
-//!
-//! # Examples
-//!
-//! An alarm clock model that prints a message when the simulation time reaches
-//! the specified timestamp.
-//!
-//! ```
-//! use asynchronix::model::Model;
-//! use asynchronix::time::{MonotonicTime, Scheduler};
-//!
-//! // An alarm clock model.
-//! pub struct AlarmClock {
-//!     msg: String
-//! }
-//!
-//! impl AlarmClock {
-//!     // Creates a new alarm clock.
-//!     pub fn new(msg: String) -> Self {
-//!         Self { msg }
-//!     }
-//!
-//!     // Sets an alarm [input port].
-//!     pub fn set(&mut self, setting: MonotonicTime, scheduler: &Scheduler<Self>) {
-//!         if scheduler.schedule_event(setting, Self::ring, ()).is_err() {
-//!             println!("The alarm clock can only be set for a future time");
-//!         }
-//!     }
-//!
-//!     // Rings the alarm [private input port].
-//!     fn ring(&mut self) {
-//!         println!("{}", self.msg);
-//!     }
-//! }
-//!
-//! impl Model for AlarmClock {}
-//! ```
-
-mod clock;
-mod monotonic_time;
-mod scheduler;
-
-pub use clock::{AutoSystemClock, Clock, NoClock, SyncStatus, SystemClock};
-pub(crate) use monotonic_time::TearableAtomicTime;
-pub use monotonic_time::{MonotonicTime, SystemTimeError};
-pub(crate) use scheduler::{
-    schedule_event_at_unchecked, schedule_keyed_event_at_unchecked,
-    schedule_periodic_event_at_unchecked, schedule_periodic_keyed_event_at_unchecked,
-    ScheduledEvent, SchedulerQueue,
-};
-pub use scheduler::{Deadline, EventKey, Scheduler, SchedulingError};

asynchronix/src/time/monotonic_time.rs

@@ -1,671 +0,0 @@
-//! Monotonic simulation time.
-
-use std::error::Error;
-use std::fmt;
-use std::ops::{Add, AddAssign, Sub, SubAssign};
-use std::sync::atomic::{AtomicI64, AtomicU32, Ordering};
-use std::time::{Duration, SystemTime};
-
-use crate::util::sync_cell::TearableAtomic;
-
-const NANOS_PER_SEC: u32 = 1_000_000_000;
-
-/// A nanosecond-precision monotonic clock timestamp.
-///
-/// A timestamp specifies a [TAI] point in time. It is represented as a 64-bit
-/// signed number of seconds and a positive number of nanoseconds, counted with
-/// reference to 1970-01-01 00:00:00 TAI. This timestamp format has a number of
-/// desirable properties:
-///
-/// - it enables cheap inter-operation with the standard [`Duration`] type which
-///   uses a very similar internal representation,
-/// - it constitutes a strict 96-bit superset of 80-bit PTP IEEE-1588
-///   timestamps, with the same epoch,
-/// - if required, exact conversion to a Unix timestamp is trivial and only
-///   requires subtracting from this timestamp the number of leap seconds
-///   between TAI and UTC time (see also the
-///   [`as_unix_secs()`](MonotonicTime::as_unix_secs) method).
-///
-/// Although no date-time conversion methods are provided, conversion from
-/// timestamp to TAI date-time representations and back can be easily performed
-/// using `NaiveDateTime` from the [chrono] crate or `OffsetDateTime` from the
-/// [time] crate, treating the timestamp as a regular (UTC) Unix timestamp.
-///
-/// [TAI]: https://en.wikipedia.org/wiki/International_Atomic_Time
-/// [chrono]: https://crates.io/crates/chrono
-/// [time]: https://crates.io/crates/time
-///
-/// # Examples
-///
-/// ```
-/// use std::time::Duration;
-/// use asynchronix::time::MonotonicTime;
-///
-/// // Set the timestamp to 2009-02-13 23:31:30.987654321 TAI.
-/// let mut timestamp = MonotonicTime::new(1_234_567_890, 987_654_321);
-///
-/// // Increment the timestamp by 123.456s.
-/// timestamp += Duration::new(123, 456_000_000);
-///
-/// assert_eq!(timestamp, MonotonicTime::new(1_234_568_014, 443_654_321));
-/// assert_eq!(timestamp.as_secs(), 1_234_568_014);
-/// assert_eq!(timestamp.subsec_nanos(), 443_654_321);
-/// ```
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
-#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
-pub struct MonotonicTime {
-    /// The number of whole seconds in the future (if positive) or in the past
-    /// (if negative) of 1970-01-01 00:00:00 TAI.
-    ///
-    /// Note that the automatic derivation of `PartialOrd` relies on
-    /// lexicographical comparison so the `secs` field must appear before
-    /// `nanos` in declaration order to be given higher priority.
-    secs: i64,
-    /// The sub-second number of nanoseconds in the future of the point in time
-    /// defined by `secs`.
-    nanos: u32,
-}
-
-impl MonotonicTime {
-    /// The epoch used by `MonotonicTime`, equal to 1970-01-01 00:00:00 TAI.
-    ///
-    /// This epoch coincides with the PTP epoch defined in the IEEE-1588
-    /// standard.
-    pub const EPOCH: Self = Self { secs: 0, nanos: 0 };
-
-    /// The minimum possible `MonotonicTime` timestamp.
-    pub const MIN: Self = Self {
-        secs: i64::MIN,
-        nanos: 0,
-    };
-
-    /// The maximum possible `MonotonicTime` timestamp.
-    pub const MAX: Self = Self {
-        secs: i64::MAX,
-        nanos: NANOS_PER_SEC - 1,
-    };
-
-    /// Creates a timestamp directly from timestamp parts.
-    ///
-    /// The number of seconds is relative to the [`EPOCH`](MonotonicTime::EPOCH)
-    /// (1970-01-01 00:00:00 TAI). It is negative for dates in the past of the
-    /// epoch.
-    ///
-    /// The number of nanoseconds is always positive and always points towards
-    /// the future.
-    ///
-    /// # Panics
-    ///
-    /// This constructor will panic if the number of nanoseconds is greater than
-    /// or equal to 1 second.
-    ///
-    /// # Example
-    ///
-    /// ```
-    /// use std::time::Duration;
-    /// use asynchronix::time::MonotonicTime;
-    ///
-    /// // A timestamp set to 2009-02-13 23:31:30.987654321 TAI.
-    /// let timestamp = MonotonicTime::new(1_234_567_890, 987_654_321);
-    ///
-    /// // A timestamp set 3.5s before the epoch.
-    /// let timestamp = MonotonicTime::new(-4, 500_000_000);
-    /// assert_eq!(timestamp, MonotonicTime::EPOCH - Duration::new(3, 500_000_000));
-    /// ```
-    pub const fn new(secs: i64, subsec_nanos: u32) -> Self {
-        assert!(
-            subsec_nanos < NANOS_PER_SEC,
-            "invalid number of nanoseconds"
-        );
-
-        Self {
-            secs,
-            nanos: subsec_nanos,
-        }
-    }
-
-    /// Creates a timestamp from the current system time.
-    ///
-    /// The argument is the current difference between TAI and UTC time in
-    /// seconds (a.k.a. leap seconds). For reference, this offset has been +37s
-    /// since 2017-01-01, a value which is to remain valid until at least
-    /// 2024-06-29. See the [official IERS bulletin
-    /// C](https://datacenter.iers.org/data/latestVersion/bulletinC.txt) for
-    /// leap second announcements or the [IETF
-    /// table](https://www.ietf.org/timezones/data/leap-seconds.list) for
-    /// current and historical values.
-    ///
-    /// # Errors
-    ///
-    /// This method will return an error if the reported system time is in the
-    /// past of the Unix epoch or if the offset-adjusted timestamp is outside
-    /// the representable range.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use asynchronix::time::MonotonicTime;
-    ///
-    /// // Compute the current TAI time assuming that the current difference
-    /// // between TAI and UTC time is 37s.
-    /// let timestamp = MonotonicTime::from_system(37).unwrap();
-    /// ```
-    pub fn from_system(leap_secs: i64) -> Result<Self, SystemTimeError> {
-        let utc_timestamp = SystemTime::now()
-            .duration_since(SystemTime::UNIX_EPOCH)
-            .map_err(|_| SystemTimeError::InvalidSystemTime)?;
-
-        Self::new(leap_secs, 0)
-            .checked_add(utc_timestamp)
-            .ok_or(SystemTimeError::OutOfRange)
-    }
-
-    /// Returns the number of whole seconds relative to
-    /// [`EPOCH`](MonotonicTime::EPOCH) (1970-01-01 00:00:00 TAI).
-    ///
-    /// Consistently with the interpretation of seconds and nanoseconds in the
-    /// [`new()`](Self::new) constructor, seconds are always rounded towards
-    /// `-∞`.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::time::Duration;
-    /// use asynchronix::time::MonotonicTime;
-    ///
-    /// let timestamp = MonotonicTime::new(1_234_567_890, 987_654_321);
-    /// assert_eq!(timestamp.as_secs(), 1_234_567_890);
-    ///
-    /// let timestamp = MonotonicTime::EPOCH - Duration::new(3, 500_000_000);
-    /// assert_eq!(timestamp.as_secs(), -4);
-    /// ```
-    pub const fn as_secs(&self) -> i64 {
-        self.secs
-    }
-
-    /// Returns the number of seconds of the corresponding Unix time.
-    ///
-    /// The argument is the difference between TAI and UTC time in seconds
-    /// (a.k.a. leap seconds) applicable at the date represented by the
-    /// timestamp. See the [official IERS bulletin
-    /// C](https://datacenter.iers.org/data/latestVersion/bulletinC.txt) for
-    /// leap second announcements or the [IETF
-    /// table](https://www.ietf.org/timezones/data/leap-seconds.list) for
-    /// current and historical values.
-    ///
-    /// This method merely subtracts the offset from the value returned by
-    /// [`as_secs()`](Self::as_secs) and checks for potential overflow; its main
-    /// purpose is to prevent mistakes regarding the direction in which the
-    /// offset should be applied.
-    ///
-    /// Note that the nanosecond part of a Unix timestamp can be simply
-    /// retrieved with [`subsec_nanos()`](Self::subsec_nanos) since UTC and TAI
-    /// differ by a whole number of seconds.
-    ///
-    /// # Panics
-    ///
-    /// This will panic if the offset-adjusted timestamp cannot be represented
-    /// as an `i64`.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use asynchronix::time::MonotonicTime;
-    ///
-    /// // Set the date to 2000-01-01 00:00:00 TAI.
-    /// let timestamp = MonotonicTime::new(946_684_800, 0);
-    ///
-    /// // Convert to a Unix timestamp, accounting for the +32s difference between
-    /// // TAI and UTC on 2000-01-01.
-    /// let unix_secs = timestamp.as_unix_secs(32);
-    /// ```
-    pub const fn as_unix_secs(&self, leap_secs: i64) -> i64 {
-        if let Some(secs) = self.secs.checked_sub(leap_secs) {
-            secs
-        } else {
-            panic!("timestamp outside representable range");
-        }
-    }
-
-    /// Returns the sub-second fractional part in nanoseconds.
-    ///
-    /// Note that nanoseconds always point towards the future even if the date
-    /// is in the past of the [`EPOCH`](MonotonicTime::EPOCH).
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use asynchronix::time::MonotonicTime;
-    ///
-    /// let timestamp = MonotonicTime::new(1_234_567_890, 987_654_321);
-    /// assert_eq!(timestamp.subsec_nanos(), 987_654_321);
-    /// ```
-    pub const fn subsec_nanos(&self) -> u32 {
-        self.nanos
-    }
-
-    /// Adds a duration to a timestamp, checking for overflow.
-    ///
-    /// Returns `None` if overflow occurred.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::time::Duration;
-    /// use asynchronix::time::MonotonicTime;
-    ///
-    /// let timestamp = MonotonicTime::new(1_234_567_890, 987_654_321);
-    /// assert!(timestamp.checked_add(Duration::new(10, 123_456_789)).is_some());
-    /// assert!(timestamp.checked_add(Duration::MAX).is_none());
-    /// ```
-    pub const fn checked_add(self, rhs: Duration) -> Option<Self> {
-        // A durations in seconds greater than `i64::MAX` is actually fine as
-        // long as the number of seconds does not effectively overflow which is
-        // why the below does not use `checked_add`. So technically the below
-        // addition may wrap around on the negative side due to the
-        // unsigned-to-signed cast of the duration, but this does not
-        // necessarily indicate an actual overflow. Actual overflow can be ruled
-        // out by verifying that the new timestamp is in the future of the old
-        // timestamp.
-        let mut secs = self.secs.wrapping_add(rhs.as_secs() as i64);
-
-        // Check for overflow.
-        if secs < self.secs {
-            return None;
-        }
-
-        let mut nanos = self.nanos + rhs.subsec_nanos();
-        if nanos >= NANOS_PER_SEC {
-            secs = if let Some(s) = secs.checked_add(1) {
-                s
-            } else {
-                return None;
-            };
-            nanos -= NANOS_PER_SEC;
-        }
-
-        Some(Self { secs, nanos })
-    }
-
-    /// Subtracts a duration from a timestamp, checking for overflow.
-    ///
-    /// Returns `None` if overflow occurred.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::time::Duration;
-    /// use asynchronix::time::MonotonicTime;
-    ///
-    /// let timestamp = MonotonicTime::new(1_234_567_890, 987_654_321);
-    /// assert!(timestamp.checked_sub(Duration::new(10, 123_456_789)).is_some());
-    /// assert!(timestamp.checked_sub(Duration::MAX).is_none());
-    /// ```
-    pub const fn checked_sub(self, rhs: Duration) -> Option<Self> {
-        // A durations in seconds greater than `i64::MAX` is actually fine as
-        // long as the number of seconds does not effectively overflow, which is
-        // why the below does not use `checked_sub`. So technically the below
-        // subtraction may wrap around on the positive side due to the
-        // unsigned-to-signed cast of the duration, but this does not
-        // necessarily indicate an actual overflow. Actual overflow can be ruled
-        // out by verifying that the new timestamp is in the past of the old
-        // timestamp.
-        let mut secs = self.secs.wrapping_sub(rhs.as_secs() as i64);
-
-        // Check for overflow.
-        if secs > self.secs {
-            return None;
-        }
-
-        let nanos = if self.nanos < rhs.subsec_nanos() {
-            secs = if let Some(s) = secs.checked_sub(1) {
-                s
-            } else {
-                return None;
-            };
-
-            (self.nanos + NANOS_PER_SEC) - rhs.subsec_nanos()
-        } else {
-            self.nanos - rhs.subsec_nanos()
-        };
-
-        Some(Self { secs, nanos })
-    }
-
-    /// Subtracts a timestamp from another timestamp.
-    ///
-    /// # Panics
-    ///
-    /// Panics if the argument lies in the future of `self`.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::time::Duration;
-    /// use asynchronix::time::MonotonicTime;
-    ///
-    /// let timestamp_earlier = MonotonicTime::new(1_234_567_879, 987_654_321);
-    /// let timestamp_later = MonotonicTime::new(1_234_567_900, 123_456_789);
-    /// assert_eq!(
-    ///     timestamp_later.duration_since(timestamp_earlier),
-    ///     Duration::new(20, 135_802_468)
-    /// );
-    /// ```
-    pub fn duration_since(self, earlier: Self) -> Duration {
-        self.checked_duration_since(earlier)
-            .expect("attempt to substract a timestamp from an earlier timestamp")
-    }
-
-    /// Computes the duration elapsed between a timestamp and an earlier
-    /// timestamp, checking that the timestamps are appropriately ordered.
-    ///
-    /// Returns `None` if the argument lies in the future of `self`.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::time::Duration;
-    /// use asynchronix::time::MonotonicTime;
-    ///
-    /// let timestamp_earlier = MonotonicTime::new(1_234_567_879, 987_654_321);
-    /// let timestamp_later = MonotonicTime::new(1_234_567_900, 123_456_789);
-    /// assert!(timestamp_later.checked_duration_since(timestamp_earlier).is_some());
-    /// assert!(timestamp_earlier.checked_duration_since(timestamp_later).is_none());
-    /// ```
-    pub const fn checked_duration_since(self, earlier: Self) -> Option<Duration> {
-        // If the subtraction of the nanosecond fractions would overflow, carry
-        // over one second to the nanoseconds.
-        let (secs, nanos) = if earlier.nanos > self.nanos {
-            if let Some(s) = self.secs.checked_sub(1) {
-                (s, self.nanos + NANOS_PER_SEC)
-            } else {
-                return None;
-            }
-        } else {
-            (self.secs, self.nanos)
-        };
-
-        // Make sure the computation of the duration will not overflow the
-        // seconds.
-        if secs < earlier.secs {
-            return None;
-        }
-
-        // This subtraction may wrap around if the difference between the two
-        // timestamps is more than `i64::MAX`, but even if it does the result
-        // will be correct once cast to an unsigned integer.
-        let delta_secs = secs.wrapping_sub(earlier.secs) as u64;
-
-        // The below subtraction is guaranteed to never overflow.
-        let delta_nanos = nanos - earlier.nanos;
-
-        Some(Duration::new(delta_secs, delta_nanos))
-    }
-}
-
-impl Add<Duration> for MonotonicTime {
-    type Output = Self;
-
-    /// Adds a duration to a timestamp.
-    ///
-    /// # Panics
-    ///
-    /// This function panics if the resulting timestamp cannot be
-    /// represented. See [`MonotonicTime::checked_add`] for a panic-free
-    /// version.
-    fn add(self, other: Duration) -> Self {
-        self.checked_add(other)
-            .expect("overflow when adding duration to timestamp")
-    }
-}
-
-impl Sub<Duration> for MonotonicTime {
-    type Output = Self;
-
-    /// Subtracts a duration from a timestamp.
-    ///
-    /// # Panics
-    ///
-    /// This function panics if the resulting timestamp cannot be
-    /// represented. See [`MonotonicTime::checked_sub`] for a panic-free
-    /// version.
-    fn sub(self, other: Duration) -> Self {
-        self.checked_sub(other)
-            .expect("overflow when subtracting duration from timestamp")
-    }
-}
-
-impl AddAssign<Duration> for MonotonicTime {
-    /// Increments the timestamp by a duration.
-    ///
-    /// # Panics
-    ///
-    /// This function panics if the resulting timestamp cannot be represented.
-    fn add_assign(&mut self, other: Duration) {
-        *self = *self + other;
-    }
-}
-
-impl SubAssign<Duration> for MonotonicTime {
-    /// Decrements the timestamp by a duration.
-    ///
-    /// # Panics
-    ///
-    /// This function panics if the resulting timestamp cannot be represented.
-    fn sub_assign(&mut self, other: Duration) {
-        *self = *self - other;
-    }
-}
-
-/// An error that may be returned when initializing a [`MonotonicTime`] from
-/// system time.
-#[derive(Debug, PartialEq, Eq, Clone, Copy)]
-pub enum SystemTimeError {
-    /// The system time is in the past of the Unix epoch.
-    InvalidSystemTime,
-    /// The system time cannot be represented as a `MonotonicTime`.
-    OutOfRange,
-}
-
-impl fmt::Display for SystemTimeError {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Self::InvalidSystemTime => write!(fmt, "invalid system time"),
-            Self::OutOfRange => write!(fmt, "timestamp outside representable range"),
-        }
-    }
-}
-
-impl Error for SystemTimeError {}
-
-/// A tearable atomic adapter over a `MonotonicTime`.
-///
-/// This makes it possible to store the simulation time in a `SyncCell`, an
-/// efficient, seqlock-based alternative to `RwLock`.
-pub(crate) struct TearableAtomicTime {
-    secs: AtomicI64,
-    nanos: AtomicU32,
-}
-
-impl TearableAtomicTime {
-    pub(crate) fn new(time: MonotonicTime) -> Self {
-        Self {
-            secs: AtomicI64::new(time.secs),
-            nanos: AtomicU32::new(time.nanos),
-        }
-    }
-}
-
-impl TearableAtomic for TearableAtomicTime {
-    type Value = MonotonicTime;
-
-    fn tearable_load(&self) -> MonotonicTime {
-        // Load each field separately. This can never create invalid values of a
-        // `MonotonicTime`, even if the load is torn.
-        MonotonicTime {
-            secs: self.secs.load(Ordering::Relaxed),
-            nanos: self.nanos.load(Ordering::Relaxed),
-        }
-    }
-
-    fn tearable_store(&self, value: MonotonicTime) {
-        // Write each field separately. This can never create invalid values of
-        // a `MonotonicTime`, even if the store is torn.
-        self.secs.store(value.secs, Ordering::Relaxed);
-        self.nanos.store(value.nanos, Ordering::Relaxed);
-    }
-}
-
-#[cfg(all(test, not(asynchronix_loom)))]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn time_equality() {
-        let t0 = MonotonicTime::new(123, 123_456_789);
-        let t1 = MonotonicTime::new(123, 123_456_789);
-        let t2 = MonotonicTime::new(123, 123_456_790);
-        let t3 = MonotonicTime::new(124, 123_456_789);
-
-        assert_eq!(t0, t1);
-        assert_ne!(t0, t2);
-        assert_ne!(t0, t3);
-    }
-
-    #[test]
-    fn time_ordering() {
-        let t0 = MonotonicTime::new(0, 1);
-        let t1 = MonotonicTime::new(1, 0);
-
-        assert!(t1 > t0);
-    }
-
-    #[cfg(not(miri))]
-    #[test]
-    fn time_from_system_smoke() {
-        const START_OF_2022: i64 = 1640995200;
-        const START_OF_2050: i64 = 2524608000;
-
-        let now_secs = MonotonicTime::from_system(0).unwrap().as_secs();
-
-        assert!(now_secs > START_OF_2022);
-        assert!(now_secs < START_OF_2050);
-    }
-
-    #[test]
-    #[should_panic]
-    fn time_invalid() {
-        MonotonicTime::new(123, 1_000_000_000);
-    }
-
-    #[test]
-    fn time_duration_since_smoke() {
-        let t0 = MonotonicTime::new(100, 100_000_000);
-        let t1 = MonotonicTime::new(123, 223_456_789);
-
-        assert_eq!(
-            t1.checked_duration_since(t0),
-            Some(Duration::new(23, 123_456_789))
-        );
-    }
-
-    #[test]
-    fn time_duration_with_carry() {
-        let t0 = MonotonicTime::new(100, 200_000_000);
-        let t1 = MonotonicTime::new(101, 100_000_000);
-
-        assert_eq!(
-            t1.checked_duration_since(t0),
-            Some(Duration::new(0, 900_000_000))
-        );
-    }
-
-    #[test]
-    fn time_duration_since_extreme() {
-        const MIN_TIME: MonotonicTime = MonotonicTime::new(i64::MIN, 0);
-        const MAX_TIME: MonotonicTime = MonotonicTime::new(i64::MAX, NANOS_PER_SEC - 1);
-
-        assert_eq!(
-            MAX_TIME.checked_duration_since(MIN_TIME),
-            Some(Duration::new(u64::MAX, NANOS_PER_SEC - 1))
-        );
-    }
-
-    #[test]
-    fn time_duration_since_invalid() {
-        let t0 = MonotonicTime::new(100, 0);
-        let t1 = MonotonicTime::new(99, 0);
-
-        assert_eq!(t1.checked_duration_since(t0), None);
-    }
-
-    #[test]
-    fn time_add_duration_smoke() {
-        let t = MonotonicTime::new(-100, 100_000_000);
-        let dt = Duration::new(400, 300_000_000);
-
-        assert_eq!(t + dt, MonotonicTime::new(300, 400_000_000));
-    }
-
-    #[test]
-    fn time_add_duration_with_carry() {
-        let t = MonotonicTime::new(-100, 900_000_000);
-        let dt1 = Duration::new(400, 100_000_000);
-        let dt2 = Duration::new(400, 300_000_000);
-
-        assert_eq!(t + dt1, MonotonicTime::new(301, 0));
-        assert_eq!(t + dt2, MonotonicTime::new(301, 200_000_000));
-    }
-
-    #[test]
-    fn time_add_duration_extreme() {
-        let t = MonotonicTime::new(i64::MIN, 0);
-        let dt = Duration::new(u64::MAX, NANOS_PER_SEC - 1);
-
-        assert_eq!(t + dt, MonotonicTime::new(i64::MAX, NANOS_PER_SEC - 1));
-    }
-
-    #[test]
-    #[should_panic]
-    fn time_add_duration_overflow() {
-        let t = MonotonicTime::new(i64::MIN, 1);
-        let dt = Duration::new(u64::MAX, NANOS_PER_SEC - 1);
-
-        let _ = t + dt;
-    }
-
-    #[test]
-    fn time_sub_duration_smoke() {
-        let t = MonotonicTime::new(100, 500_000_000);
-        let dt = Duration::new(400, 300_000_000);
-
-        assert_eq!(t - dt, MonotonicTime::new(-300, 200_000_000));
-    }
-
-    #[test]
-    fn time_sub_duration_with_carry() {
-        let t = MonotonicTime::new(100, 100_000_000);
-        let dt1 = Duration::new(400, 100_000_000);
-        let dt2 = Duration::new(400, 300_000_000);
-
-        assert_eq!(t - dt1, MonotonicTime::new(-300, 0));
-        assert_eq!(t - dt2, MonotonicTime::new(-301, 800_000_000));
-    }
-
-    #[test]
-    fn time_sub_duration_extreme() {
-        let t = MonotonicTime::new(i64::MAX, NANOS_PER_SEC - 1);
-        let dt = Duration::new(u64::MAX, NANOS_PER_SEC - 1);
-
-        assert_eq!(t - dt, MonotonicTime::new(i64::MIN, 0));
-    }
-
-    #[test]
-    #[should_panic]
-    fn time_sub_duration_overflow() {
-        let t = MonotonicTime::new(i64::MAX, NANOS_PER_SEC - 2);
-        let dt = Duration::new(u64::MAX, NANOS_PER_SEC - 1);
-
-        let _ = t - dt;
-    }
-}

asynchronix/src/time/scheduler.rs

@@ -1,943 +0,0 @@
-//! Scheduling functions and types.
-
-use std::error::Error;
-use std::fmt;
-use std::future::Future;
-use std::marker::PhantomData;
-use std::pin::Pin;
-use std::sync::atomic::{AtomicBool, Ordering};
-use std::sync::{Arc, Mutex};
-use std::task::{Context, Poll};
-use std::time::Duration;
-
-use pin_project_lite::pin_project;
-use recycle_box::{coerce_box, RecycleBox};
-
-use crate::channel::{ChannelId, Sender};
-use crate::executor::Executor;
-use crate::model::{InputFn, Model};
-use crate::time::{MonotonicTime, TearableAtomicTime};
-use crate::util::priority_queue::PriorityQueue;
-use crate::util::sync_cell::SyncCellReader;
-
-/// Shorthand for the scheduler queue type.
-pub(crate) type SchedulerQueue = PriorityQueue<(MonotonicTime, ChannelId), Box<dyn ScheduledEvent>>;
-
-/// Trait abstracting over time-absolute and time-relative deadlines.
-///
-/// This trait is implemented by [`std::time::Duration`] and
-/// [`MonotonicTime`].
-pub trait Deadline {
-    /// Make this deadline into an absolute timestamp, using the provided
-    /// current time as a reference.
-    fn into_time(self, now: MonotonicTime) -> MonotonicTime;
-}
-
-impl Deadline for Duration {
-    #[inline(always)]
-    fn into_time(self, now: MonotonicTime) -> MonotonicTime {
-        now + self
-    }
-}
-
-impl Deadline for MonotonicTime {
-    #[inline(always)]
-    fn into_time(self, _: MonotonicTime) -> MonotonicTime {
-        self
-    }
-}
-
-/// A local scheduler for models.
-///
-/// A `Scheduler` is a handle to the global scheduler associated to a model
-/// instance. It can be used by the model to retrieve the simulation time or
-/// schedule delayed actions on itself.
-///
-/// ### Caveat: self-scheduling `async` methods
-///
-/// Due to a current rustc issue, `async` methods that schedule themselves will
-/// not compile unless an explicit `Send` bound is added to the returned future.
-/// This can be done by replacing the `async` signature with a partially
-/// desugared signature such as:
-///
-/// ```ignore
-/// fn self_scheduling_method<'a>(
-///     &'a mut self,
-///     arg: MyEventType,
-///     scheduler: &'a Scheduler<Self>
-/// ) -> impl Future<Output=()> + Send + 'a {
-///     async move {
-///         /* implementation */
-///     }
-/// }
-/// ```
-///
-/// Self-scheduling methods which are not `async` are not affected by this
-/// issue.
-///
-/// # Examples
-///
-/// A model that sends a greeting after some delay.
-///
-/// ```
-/// use std::time::Duration;
-/// use asynchronix::model::{Model, Output}; use asynchronix::time::Scheduler;
-///
-/// #[derive(Default)]
-/// pub struct DelayedGreeter {
-///     msg_out: Output<String>,
-/// }
-///
-/// impl DelayedGreeter {
-///     // Triggers a greeting on the output port after some delay [input port].
-///     pub async fn greet_with_delay(&mut self, delay: Duration, scheduler: &Scheduler<Self>) {
-///         let time = scheduler.time();
-///         let greeting = format!("Hello, this message was scheduled at: {:?}.", time);
-///         
-///         if delay.is_zero() {
-///             self.msg_out.send(greeting).await;
-///         } else {
-///             scheduler.schedule_event(delay, Self::send_msg, greeting).unwrap();
-///         }
-///     }
-///
-///     // Sends a message to the output [private input port].
-///     async fn send_msg(&mut self, msg: String) {
-///         self.msg_out.send(msg).await;
-///     }
-/// }
-/// impl Model for DelayedGreeter {}
-/// ```
-
-// The self-scheduling caveat seems related to this issue:
-// https://github.com/rust-lang/rust/issues/78649
-pub struct Scheduler<M: Model> {
-    sender: Sender<M>,
-    scheduler_queue: Arc<Mutex<SchedulerQueue>>,
-    time: SyncCellReader<TearableAtomicTime>,
-}
-
-impl<M: Model> Scheduler<M> {
-    /// Creates a new local scheduler.
-    pub(crate) fn new(
-        sender: Sender<M>,
-        scheduler_queue: Arc<Mutex<SchedulerQueue>>,
-        time: SyncCellReader<TearableAtomicTime>,
-    ) -> Self {
-        Self {
-            sender,
-            scheduler_queue,
-            time,
-        }
-    }
-
-    /// Returns the current simulation time.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use asynchronix::model::Model;
-    /// use asynchronix::time::{MonotonicTime, Scheduler};
-    ///
-    /// fn is_third_millenium<M: Model>(scheduler: &Scheduler<M>) -> bool {
-    ///     let time = scheduler.time();
-    ///
-    ///     time >= MonotonicTime::new(978307200, 0) && time < MonotonicTime::new(32535216000, 0)
-    /// }
-    /// ```
-    pub fn time(&self) -> MonotonicTime {
-        self.time.try_read().expect("internal simulation error: could not perform a synchronized read of the simulation time")
-    }
-
-    /// Schedules an event at a future time.
-    ///
-    /// An error is returned if the specified deadline is not in the future of
-    /// the current simulation time.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::time::Duration;
-    ///
-    /// use asynchronix::model::Model;
-    /// use asynchronix::time::Scheduler;
-    ///
-    /// // A timer.
-    /// pub struct Timer {}
-    ///
-    /// impl Timer {
-    ///     // Sets an alarm [input port].
-    ///     pub fn set(&mut self, setting: Duration, scheduler: &Scheduler<Self>) {
-    ///         if scheduler.schedule_event(setting, Self::ring, ()).is_err() {
-    ///             println!("The alarm clock can only be set for a future time");
-    ///         }
-    ///     }
-    ///
-    ///     // Rings [private input port].
-    ///     fn ring(&mut self) {
-    ///         println!("Brringggg");
-    ///     }
-    /// }
-    ///
-    /// impl Model for Timer {}
-    /// ```
-    pub fn schedule_event<F, T, S>(
-        &self,
-        deadline: impl Deadline,
-        func: F,
-        arg: T,
-    ) -> Result<(), SchedulingError>
-    where
-        F: for<'a> InputFn<'a, M, T, S>,
-        T: Send + Clone + 'static,
-        S: Send + 'static,
-    {
-        let now = self.time();
-        let time = deadline.into_time(now);
-        if now >= time {
-            return Err(SchedulingError::InvalidScheduledTime);
-        }
-        let sender = self.sender.clone();
-        schedule_event_at_unchecked(time, func, arg, sender, &self.scheduler_queue);
-
-        Ok(())
-    }
-
-    /// Schedules a cancellable event at a future time and returns an event key.
-    ///
-    /// An error is returned if the specified deadline is not in the future of
-    /// the current simulation time.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use asynchronix::model::Model;
-    /// use asynchronix::time::{EventKey, MonotonicTime, Scheduler};
-    ///
-    /// // An alarm clock that can be cancelled.
-    /// #[derive(Default)]
-    /// pub struct CancellableAlarmClock {
-    ///     event_key: Option<EventKey>,
-    /// }
-    ///
-    /// impl CancellableAlarmClock {
-    ///     // Sets an alarm [input port].
-    ///     pub fn set(&mut self, setting: MonotonicTime, scheduler: &Scheduler<Self>) {
-    ///         self.cancel();
-    ///         match scheduler.schedule_keyed_event(setting, Self::ring, ()) {
-    ///             Ok(event_key) => self.event_key = Some(event_key),
-    ///             Err(_) => println!("The alarm clock can only be set for a future time"),
-    ///         };
-    ///     }
-    ///
-    ///     // Cancels the current alarm, if any [input port].
-    ///     pub fn cancel(&mut self) {
-    ///         self.event_key.take().map(|k| k.cancel());
-    ///     }
-    ///
-    ///     // Rings the alarm [private input port].
-    ///     fn ring(&mut self) {
-    ///         println!("Brringggg!");
-    ///     }
-    /// }
-    ///
-    /// impl Model for CancellableAlarmClock {}
-    /// ```
-    pub fn schedule_keyed_event<F, T, S>(
-        &self,
-        deadline: impl Deadline,
-        func: F,
-        arg: T,
-    ) -> Result<EventKey, SchedulingError>
-    where
-        F: for<'a> InputFn<'a, M, T, S>,
-        T: Send + Clone + 'static,
-        S: Send + 'static,
-    {
-        let now = self.time();
-        let time = deadline.into_time(now);
-        if now >= time {
-            return Err(SchedulingError::InvalidScheduledTime);
-        }
-        let sender = self.sender.clone();
-        let event_key =
-            schedule_keyed_event_at_unchecked(time, func, arg, sender, &self.scheduler_queue);
-
-        Ok(event_key)
-    }
-
-    /// Schedules a periodically recurring event at a future time.
-    ///
-    /// An error is returned if the specified deadline is not in the future of
-    /// the current simulation time or if the specified period is null.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::time::Duration;
-    ///
-    /// use asynchronix::model::Model;
-    /// use asynchronix::time::{MonotonicTime, Scheduler};
-    ///
-    /// // An alarm clock beeping at 1Hz.
-    /// pub struct BeepingAlarmClock {}
-    ///
-    /// impl BeepingAlarmClock {
-    ///     // Sets an alarm [input port].
-    ///     pub fn set(&mut self, setting: MonotonicTime, scheduler: &Scheduler<Self>) {
-    ///         if scheduler.schedule_periodic_event(
-    ///             setting,
-    ///             Duration::from_secs(1), // 1Hz = 1/1s
-    ///             Self::beep,
-    ///             ()
-    ///         ).is_err() {
-    ///             println!("The alarm clock can only be set for a future time");
-    ///         }
-    ///     }
-    ///
-    ///     // Emits a single beep [private input port].
-    ///     fn beep(&mut self) {
-    ///         println!("Beep!");
-    ///     }
-    /// }
-    ///
-    /// impl Model for BeepingAlarmClock {}
-    /// ```
-    pub fn schedule_periodic_event<F, T, S>(
-        &self,
-        deadline: impl Deadline,
-        period: Duration,
-        func: F,
-        arg: T,
-    ) -> Result<(), SchedulingError>
-    where
-        F: for<'a> InputFn<'a, M, T, S> + Clone,
-        T: Send + Clone + 'static,
-        S: Send + 'static,
-    {
-        let now = self.time();
-        let time = deadline.into_time(now);
-        if now >= time {
-            return Err(SchedulingError::InvalidScheduledTime);
-        }
-        if period.is_zero() {
-            return Err(SchedulingError::NullRepetitionPeriod);
-        }
-        let sender = self.sender.clone();
-        schedule_periodic_event_at_unchecked(
-            time,
-            period,
-            func,
-            arg,
-            sender,
-            &self.scheduler_queue,
-        );
-
-        Ok(())
-    }
-
-    /// Schedules a cancellable, periodically recurring event at a future time
-    /// and returns an event key.
-    ///
-    /// An error is returned if the specified deadline is not in the future of
-    /// the current simulation time or if the specified period is null.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::time::Duration;
-    ///
-    /// use asynchronix::model::Model;
-    /// use asynchronix::time::{EventKey, MonotonicTime, Scheduler};
-    ///
-    /// // An alarm clock beeping at 1Hz that can be cancelled before it sets off, or
-    /// // stopped after it sets off.
-    /// #[derive(Default)]
-    /// pub struct CancellableBeepingAlarmClock {
-    ///     event_key: Option<EventKey>,
-    /// }
-    ///
-    /// impl CancellableBeepingAlarmClock {
-    ///     // Sets an alarm [input port].
-    ///     pub fn set(&mut self, setting: MonotonicTime, scheduler: &Scheduler<Self>) {
-    ///         self.cancel();
-    ///         match scheduler.schedule_keyed_periodic_event(
-    ///             setting,
-    ///             Duration::from_secs(1), // 1Hz = 1/1s
-    ///             Self::beep,
-    ///             ()
-    ///         ) {
-    ///             Ok(event_key) => self.event_key = Some(event_key),
-    ///             Err(_) => println!("The alarm clock can only be set for a future time"),
-    ///         };
-    ///     }
-    ///
-    ///     // Cancels or stops the alarm [input port].
-    ///     pub fn cancel(&mut self) {
-    ///         self.event_key.take().map(|k| k.cancel());
-    ///     }
-    ///
-    ///     // Emits a single beep [private input port].
-    ///     fn beep(&mut self) {
-    ///         println!("Beep!");
-    ///     }
-    /// }
-    ///
-    /// impl Model for CancellableBeepingAlarmClock {}
-    /// ```
-    pub fn schedule_keyed_periodic_event<F, T, S>(
-        &self,
-        deadline: impl Deadline,
-        period: Duration,
-        func: F,
-        arg: T,
-    ) -> Result<EventKey, SchedulingError>
-    where
-        F: for<'a> InputFn<'a, M, T, S> + Clone,
-        T: Send + Clone + 'static,
-        S: Send + 'static,
-    {
-        let now = self.time();
-        let time = deadline.into_time(now);
-        if now >= time {
-            return Err(SchedulingError::InvalidScheduledTime);
-        }
-        if period.is_zero() {
-            return Err(SchedulingError::NullRepetitionPeriod);
-        }
-        let sender = self.sender.clone();
-        let event_key = schedule_periodic_keyed_event_at_unchecked(
-            time,
-            period,
-            func,
-            arg,
-            sender,
-            &self.scheduler_queue,
-        );
-
-        Ok(event_key)
-    }
-}
-
-impl<M: Model> fmt::Debug for Scheduler<M> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        f.debug_struct("Scheduler").finish_non_exhaustive()
-    }
-}
-
-/// Handle to a scheduled event.
-///
-/// An `EventKey` can be used to cancel a future event.
-#[derive(Clone, Debug)]
-#[must_use = "prefer unkeyed scheduling methods if the event is never cancelled"]
-pub struct EventKey {
-    is_cancelled: Arc<AtomicBool>,
-}
-
-impl EventKey {
-    /// Creates a key for a pending event.
-    pub(crate) fn new() -> Self {
-        Self {
-            is_cancelled: Arc::new(AtomicBool::new(false)),
-        }
-    }
-
-    /// Checks whether the event was cancelled.
-    pub(crate) fn is_cancelled(&self) -> bool {
-        self.is_cancelled.load(Ordering::Relaxed)
-    }
-
-    /// Cancels the associated event.
-    pub fn cancel(self) {
-        self.is_cancelled.store(true, Ordering::Relaxed);
-    }
-}
-
-/// Error returned when the scheduled time or the repetition period are invalid.
-#[derive(Debug, PartialEq, Eq, Clone, Copy)]
-pub enum SchedulingError {
-    /// The scheduled time does not lie in the future of the current simulation
-    /// time.
-    InvalidScheduledTime,
-    /// The repetition period is zero.
-    NullRepetitionPeriod,
-}
-
-impl fmt::Display for SchedulingError {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Self::InvalidScheduledTime => write!(
-                fmt,
-                "the scheduled time should be in the future of the current simulation time"
-            ),
-            Self::NullRepetitionPeriod => write!(fmt, "the repetition period cannot be zero"),
-        }
-    }
-}
-
-impl Error for SchedulingError {}
-
-/// Schedules an event at a future time.
-///
-/// This method does not check whether the specified time lies in the future
-/// of the current simulation time.
-pub(crate) fn schedule_event_at_unchecked<M, F, T, S>(
-    time: MonotonicTime,
-    func: F,
-    arg: T,
-    sender: Sender<M>,
-    scheduler_queue: &Mutex<SchedulerQueue>,
-) where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S>,
-    T: Send + Clone + 'static,
-    S: Send + 'static,
-{
-    let channel_id = sender.channel_id();
-
-    let event_dispatcher = Box::new(new_event_dispatcher(func, arg, sender));
-
-    let mut scheduler_queue = scheduler_queue.lock().unwrap();
-    scheduler_queue.insert((time, channel_id), event_dispatcher);
-}
-
-/// Schedules an event at a future time, returning an event key.
-///
-/// This method does not check whether the specified time lies in the future
-/// of the current simulation time.
-pub(crate) fn schedule_keyed_event_at_unchecked<M, F, T, S>(
-    time: MonotonicTime,
-    func: F,
-    arg: T,
-    sender: Sender<M>,
-    scheduler_queue: &Mutex<SchedulerQueue>,
-) -> EventKey
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S>,
-    T: Send + Clone + 'static,
-    S: Send + 'static,
-{
-    let event_key = EventKey::new();
-    let channel_id = sender.channel_id();
-    let event_dispatcher = Box::new(KeyedEventDispatcher::new(
-        event_key.clone(),
-        func,
-        arg,
-        sender,
-    ));
-
-    let mut scheduler_queue = scheduler_queue.lock().unwrap();
-    scheduler_queue.insert((time, channel_id), event_dispatcher);
-
-    event_key
-}
-
-/// Schedules a periodic event at a future time.
-///
-/// This method does not check whether the specified time lies in the future
-/// of the current simulation time.
-pub(crate) fn schedule_periodic_event_at_unchecked<M, F, T, S>(
-    time: MonotonicTime,
-    period: Duration,
-    func: F,
-    arg: T,
-    sender: Sender<M>,
-    scheduler_queue: &Mutex<SchedulerQueue>,
-) where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S> + Clone,
-    T: Send + Clone + 'static,
-    S: Send + 'static,
-{
-    let channel_id = sender.channel_id();
-
-    let event_dispatcher = Box::new(PeriodicEventDispatcher::new(func, arg, sender, period));
-
-    let mut scheduler_queue = scheduler_queue.lock().unwrap();
-    scheduler_queue.insert((time, channel_id), event_dispatcher);
-}
-
-/// Schedules an event at a future time, returning an event key.
-///
-/// This method does not check whether the specified time lies in the future
-/// of the current simulation time.
-pub(crate) fn schedule_periodic_keyed_event_at_unchecked<M, F, T, S>(
-    time: MonotonicTime,
-    period: Duration,
-    func: F,
-    arg: T,
-    sender: Sender<M>,
-    scheduler_queue: &Mutex<SchedulerQueue>,
-) -> EventKey
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S> + Clone,
-    T: Send + Clone + 'static,
-    S: Send + 'static,
-{
-    let event_key = EventKey::new();
-    let channel_id = sender.channel_id();
-    let event_dispatcher = Box::new(PeriodicKeyedEventDispatcher::new(
-        event_key.clone(),
-        func,
-        arg,
-        sender,
-        period,
-    ));
-
-    let mut scheduler_queue = scheduler_queue.lock().unwrap();
-    scheduler_queue.insert((time, channel_id), event_dispatcher);
-
-    event_key
-}
-
-/// Trait for objects that can be converted to a future dispatching a scheduled
-/// event.
-pub(crate) trait ScheduledEvent: Send {
-    /// Reports whether the associated event was cancelled.
-    fn is_cancelled(&self) -> bool;
-
-    /// Returns a boxed clone of this event and the repetition period if this is
-    /// a periodic even, otherwise returns `None`.
-    fn next(&self) -> Option<(Box<dyn ScheduledEvent>, Duration)>;
-
-    /// Returns a boxed future dispatching the associated event.
-    fn into_future(self: Box<Self>) -> Pin<Box<dyn Future<Output = ()> + Send>>;
-
-    /// Spawns the future that dispatches the associated event onto the provided
-    /// executor.
-    ///
-    /// This method is typically more efficient that spawning the boxed future
-    /// from `into_future` since it can directly spawn the unboxed future.
-    fn spawn_and_forget(self: Box<Self>, executor: &Executor);
-}
-
-pin_project! {
-    /// Object that can be converted to a future dispatching a non-cancellable
-    /// event.
-    ///
-    /// Note that this particular event dispatcher is in fact already a future:
-    /// since the future cannot be cancelled and the dispatcher does not need to
-    /// be cloned, there is no need to defer the construction of the future.
-    /// This makes `into_future` a trivial cast, which saves a boxing operation.
-    pub(crate) struct EventDispatcher<F> {
-        #[pin]
-        fut: F,
-    }
-}
-
-/// Constructs a new `EventDispatcher`.
-///
-/// Due to some limitations of type inference or of my understanding of it, the
-/// constructor for this event dispatchers is a freestanding function.
-fn new_event_dispatcher<M, F, T, S>(
-    func: F,
-    arg: T,
-    sender: Sender<M>,
-) -> EventDispatcher<impl Future<Output = ()>>
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S>,
-    T: Send + Clone + 'static,
-{
-    let fut = dispatch_event(func, arg, sender);
-
-    EventDispatcher { fut }
-}
-
-impl<F> Future for EventDispatcher<F>
-where
-    F: Future,
-{
-    type Output = F::Output;
-
-    #[inline(always)]
-    fn poll(self: std::pin::Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        self.project().fut.poll(cx)
-    }
-}
-
-impl<F> ScheduledEvent for EventDispatcher<F>
-where
-    F: Future<Output = ()> + Send + 'static,
-{
-    fn is_cancelled(&self) -> bool {
-        false
-    }
-    fn next(&self) -> Option<(Box<dyn ScheduledEvent>, Duration)> {
-        None
-    }
-    fn into_future(self: Box<Self>) -> Pin<Box<dyn Future<Output = ()> + Send>> {
-        // No need for boxing, type coercion is enough here.
-        Box::into_pin(self)
-    }
-    fn spawn_and_forget(self: Box<Self>, executor: &Executor) {
-        executor.spawn_and_forget(*self);
-    }
-}
-
-/// Object that can be converted to a future dispatching a non-cancellable periodic
-/// event.
-pub(crate) struct PeriodicEventDispatcher<M, F, T, S>
-where
-    M: Model,
-{
-    func: F,
-    arg: T,
-    sender: Sender<M>,
-    period: Duration,
-    _input_kind: PhantomData<S>,
-}
-
-impl<M, F, T, S> PeriodicEventDispatcher<M, F, T, S>
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S>,
-    T: Send + Clone + 'static,
-{
-    /// Constructs a new `PeriodicEventDispatcher`.
-    fn new(func: F, arg: T, sender: Sender<M>, period: Duration) -> Self {
-        Self {
-            func,
-            arg,
-            sender,
-            period,
-            _input_kind: PhantomData,
-        }
-    }
-}
-
-impl<M, F, T, S> ScheduledEvent for PeriodicEventDispatcher<M, F, T, S>
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S> + Clone,
-    T: Send + Clone + 'static,
-    S: Send + 'static,
-{
-    fn is_cancelled(&self) -> bool {
-        false
-    }
-    fn next(&self) -> Option<(Box<dyn ScheduledEvent>, Duration)> {
-        let event = Box::new(Self::new(
-            self.func.clone(),
-            self.arg.clone(),
-            self.sender.clone(),
-            self.period,
-        ));
-
-        Some((event, self.period))
-    }
-    fn into_future(self: Box<Self>) -> Pin<Box<dyn Future<Output = ()> + Send>> {
-        let Self {
-            func, arg, sender, ..
-        } = *self;
-
-        Box::pin(dispatch_event(func, arg, sender))
-    }
-    fn spawn_and_forget(self: Box<Self>, executor: &Executor) {
-        let Self {
-            func, arg, sender, ..
-        } = *self;
-
-        let fut = dispatch_event(func, arg, sender);
-        executor.spawn_and_forget(fut);
-    }
-}
-
-/// Object that can be converted to a future dispatching a cancellable event.
-pub(crate) struct KeyedEventDispatcher<M, F, T, S>
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S>,
-    T: Send + Clone + 'static,
-{
-    event_key: EventKey,
-    func: F,
-    arg: T,
-    sender: Sender<M>,
-    _input_kind: PhantomData<S>,
-}
-
-impl<M, F, T, S> KeyedEventDispatcher<M, F, T, S>
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S>,
-    T: Send + Clone + 'static,
-{
-    /// Constructs a new `KeyedEventDispatcher`.
-    fn new(event_key: EventKey, func: F, arg: T, sender: Sender<M>) -> Self {
-        Self {
-            event_key,
-            func,
-            arg,
-            sender,
-            _input_kind: PhantomData,
-        }
-    }
-}
-
-impl<M, F, T, S> ScheduledEvent for KeyedEventDispatcher<M, F, T, S>
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S>,
-    T: Send + Clone + 'static,
-    S: Send + 'static,
-{
-    fn is_cancelled(&self) -> bool {
-        self.event_key.is_cancelled()
-    }
-    fn next(&self) -> Option<(Box<dyn ScheduledEvent>, Duration)> {
-        None
-    }
-    fn into_future(self: Box<Self>) -> Pin<Box<dyn Future<Output = ()> + Send>> {
-        let Self {
-            event_key,
-            func,
-            arg,
-            sender,
-            ..
-        } = *self;
-
-        Box::pin(dispatch_keyed_event(event_key, func, arg, sender))
-    }
-    fn spawn_and_forget(self: Box<Self>, executor: &Executor) {
-        let Self {
-            event_key,
-            func,
-            arg,
-            sender,
-            ..
-        } = *self;
-
-        let fut = dispatch_keyed_event(event_key, func, arg, sender);
-        executor.spawn_and_forget(fut);
-    }
-}
-
-/// Object that can be converted to a future dispatching a cancellable event.
-pub(crate) struct PeriodicKeyedEventDispatcher<M, F, T, S>
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S>,
-    T: Send + Clone + 'static,
-{
-    event_key: EventKey,
-    func: F,
-    arg: T,
-    sender: Sender<M>,
-    period: Duration,
-    _input_kind: PhantomData<S>,
-}
-
-impl<M, F, T, S> PeriodicKeyedEventDispatcher<M, F, T, S>
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S>,
-    T: Send + Clone + 'static,
-{
-    /// Constructs a new `KeyedEventDispatcher`.
-    fn new(event_key: EventKey, func: F, arg: T, sender: Sender<M>, period: Duration) -> Self {
-        Self {
-            event_key,
-            func,
-            arg,
-            sender,
-            period,
-            _input_kind: PhantomData,
-        }
-    }
-}
-
-impl<M, F, T, S> ScheduledEvent for PeriodicKeyedEventDispatcher<M, F, T, S>
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S> + Clone,
-    T: Send + Clone + 'static,
-    S: Send + 'static,
-{
-    fn is_cancelled(&self) -> bool {
-        self.event_key.is_cancelled()
-    }
-    fn next(&self) -> Option<(Box<dyn ScheduledEvent>, Duration)> {
-        let event = Box::new(Self::new(
-            self.event_key.clone(),
-            self.func.clone(),
-            self.arg.clone(),
-            self.sender.clone(),
-            self.period,
-        ));
-
-        Some((event, self.period))
-    }
-    fn into_future(self: Box<Self>) -> Pin<Box<dyn Future<Output = ()> + Send>> {
-        let Self {
-            event_key,
-            func,
-            arg,
-            sender,
-            ..
-        } = *self;
-
-        Box::pin(dispatch_keyed_event(event_key, func, arg, sender))
-    }
-    fn spawn_and_forget(self: Box<Self>, executor: &Executor) {
-        let Self {
-            event_key,
-            func,
-            arg,
-            sender,
-            ..
-        } = *self;
-
-        let fut = dispatch_keyed_event(event_key, func, arg, sender);
-        executor.spawn_and_forget(fut);
-    }
-}
-
-/// Asynchronously dispatch a regular, non-cancellable event.
-async fn dispatch_event<M, F, T, S>(func: F, arg: T, sender: Sender<M>)
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S>,
-    T: Send + Clone + 'static,
-{
-    let _ = sender
-        .send(
-            move |model: &mut M,
-                  scheduler,
-                  recycle_box: RecycleBox<()>|
-                  -> RecycleBox<dyn Future<Output = ()> + Send + '_> {
-                let fut = func.call(model, arg, scheduler);
-
-                coerce_box!(RecycleBox::recycle(recycle_box, fut))
-            },
-        )
-        .await;
-}
-
-/// Asynchronously dispatch a cancellable event.
-async fn dispatch_keyed_event<M, F, T, S>(event_key: EventKey, func: F, arg: T, sender: Sender<M>)
-where
-    M: Model,
-    F: for<'a> InputFn<'a, M, T, S>,
-    T: Send + Clone + 'static,
-{
-    let _ = sender
-        .send(
-            move |model: &mut M,
-                  scheduler,
-                  recycle_box: RecycleBox<()>|
-                  -> RecycleBox<dyn Future<Output = ()> + Send + '_> {
-                let fut = async move {
-                    // Only perform the call if the event wasn't cancelled.
-                    if !event_key.is_cancelled() {
-                        func.call(model, arg, scheduler).await;
-                    }
-                };
-
-                coerce_box!(RecycleBox::recycle(recycle_box, fut))
-            },
-        )
-        .await;
-}

asynchronix/src/util.rs

@@ -1,7 +0,0 @@
-pub(crate) mod bit;
-pub(crate) mod futures;
-pub(crate) mod priority_queue;
-pub(crate) mod rng;
-pub(crate) mod slot;
-pub(crate) mod spsc_queue;
-pub(crate) mod sync_cell;

asynchronix/src/util/spsc_queue.rs

@@ -1,393 +0,0 @@
-//! Single-producer single-consumer unbounded FIFO queue that stores values in
-//! fixed-size memory segments.
-
-#![allow(unused)]
-
-use std::cell::Cell;
-use std::error::Error;
-use std::fmt;
-use std::marker::PhantomData;
-use std::mem::MaybeUninit;
-use std::panic::{RefUnwindSafe, UnwindSafe};
-use std::ptr::{self, NonNull};
-use std::sync::atomic::Ordering;
-
-use crossbeam_utils::CachePadded;
-
-use crate::loom_exports::cell::UnsafeCell;
-use crate::loom_exports::sync::atomic::{AtomicBool, AtomicPtr};
-use crate::loom_exports::sync::Arc;
-
-/// The number of slots in a single segment.
-const SEGMENT_LEN: usize = 32;
-
-/// A slot containing a single value.
-struct Slot<T> {
-    has_value: AtomicBool,
-    value: UnsafeCell<MaybeUninit<T>>,
-}
-
-impl<T> Default for Slot<T> {
-    fn default() -> Self {
-        Slot {
-            has_value: AtomicBool::new(false),
-            value: UnsafeCell::new(MaybeUninit::uninit()),
-        }
-    }
-}
-
-/// A memory segment containing `SEGMENT_LEN` slots.
-struct Segment<T> {
-    /// Address of the next segment.
-    ///
-    /// A null pointer means that the next segment is not allocated yet.
-    next_segment: AtomicPtr<Segment<T>>,
-    data: [Slot<T>; SEGMENT_LEN],
-}
-
-impl<T> Segment<T> {
-    /// Allocates a new segment.
-    fn allocate_new() -> NonNull<Self> {
-        let segment = Self {
-            next_segment: AtomicPtr::new(ptr::null_mut()),
-            data: Default::default(),
-        };
-
-        // Safety: the pointer is non-null since it comes from a box.
-        unsafe { NonNull::new_unchecked(Box::into_raw(Box::new(segment))) }
-    }
-}
-
-/// The head of the queue from which values are popped.
-struct Head<T> {
-    /// Pointer to the segment at the head of the queue.
-    segment: NonNull<Segment<T>>,
-    /// Index of the next value to be read.
-    ///
-    /// If the index is equal to the segment length, it is necessary to move to
-    /// the next segment before the next value can be read.
-    next_read_idx: usize,
-}
-
-/// The tail of the queue to which values are pushed.
-struct Tail<T> {
-    /// Pointer to the segment at the tail of the queue.
-    segment: NonNull<Segment<T>>,
-    /// Index of the next value to be written.
-    ///
-    /// If the index is equal to the segment length, a new segment must be
-    /// allocated before a new value can be written.
-    next_write_idx: usize,
-}
-
-/// A single-producer, single-consumer unbounded FIFO queue.
-struct Queue<T> {
-    head: CachePadded<UnsafeCell<Head<T>>>,
-    tail: CachePadded<UnsafeCell<Tail<T>>>,
-}
-
-impl<T> Queue<T> {
-    /// Creates a new queue.
-    fn new() -> Self {
-        let segment = Segment::allocate_new();
-
-        let head = Head {
-            segment,
-            next_read_idx: 0,
-        };
-        let tail = Tail {
-            segment,
-            next_write_idx: 0,
-        };
-
-        Self {
-            head: CachePadded::new(UnsafeCell::new(head)),
-            tail: CachePadded::new(UnsafeCell::new(tail)),
-        }
-    }
-
-    /// Pushes a new value.
-    ///
-    /// # Safety
-    ///
-    /// The method cannot be called from multiple threads concurrently.
-    unsafe fn push(&self, value: T) {
-        // Safety: this is the only thread accessing the tail.
-        let tail = self.tail.with_mut(|p| &mut *p);
-
-        // If the whole segment has been written, allocate a new segment.
-        if tail.next_write_idx == SEGMENT_LEN {
-            let old_segment = tail.segment;
-            tail.segment = Segment::allocate_new();
-
-            // Safety: the old segment is still allocated since the consumer
-            // cannot deallocate it before `next_segment` is set to a non-null
-            // value.
-            old_segment
-                .as_ref()
-                .next_segment
-                .store(tail.segment.as_ptr(), Ordering::Release);
-
-            tail.next_write_idx = 0;
-        }
-
-        // Safety: the tail segment is allocated since the consumer cannot
-        // deallocate it before `next_segment` is set to a non-null value.
-        let data = &tail.segment.as_ref().data[tail.next_write_idx];
-
-        // Safety: we have exclusive access to the slot value since the consumer
-        // cannot access it before `has_value` is set to true.
-        data.value.with_mut(|p| (*p).write(value));
-
-        // Ordering: this Release store synchronizes with the Acquire load in
-        // `pop` and ensures that the value is visible to the consumer once
-        // `has_value` reads `true`.
-        data.has_value.store(true, Ordering::Release);
-
-        tail.next_write_idx += 1;
-    }
-
-    /// Pops a new value.
-    ///
-    /// # Safety
-    ///
-    /// The method cannot be called from multiple threads concurrently.
-    unsafe fn pop(&self) -> Option<T> {
-        // Safety: this is the only thread accessing the head.
-        let head = self.head.with_mut(|p| &mut *p);
-
-        // If the whole segment has been read, try to move to the next segment.
-        if head.next_read_idx == SEGMENT_LEN {
-            // Read the next segment or return `None` if it is not ready yet.
-            //
-            // Safety: the head segment is still allocated since we are the only
-            // thread that can deallocate it.
-            let next_segment = head.segment.as_ref().next_segment.load(Ordering::Acquire);
-            let next_segment = NonNull::new(next_segment)?;
-
-            // Deallocate the old segment.
-            //
-            // Safety: the pointer was initialized from a box and the segment is
-            // still allocated since we are the only thread that can deallocate
-            // it.
-            let _ = Box::from_raw(head.segment.as_ptr());
-
-            // Update the segment and the next index.
-            head.segment = next_segment;
-            head.next_read_idx = 0;
-        }
-
-        let data = &head.segment.as_ref().data[head.next_read_idx];
-
-        // Ordering: this Acquire load synchronizes with the Release store in
-        // `push` and ensures that the value is visible once `has_value` reads
-        // `true`.
-        if !data.has_value.load(Ordering::Acquire) {
-            return None;
-        }
-
-        // Safety: since `has_value` is `true` then we have exclusive ownership
-        // of the value and we know that it was initialized.
-        let value = data.value.with(|p| (*p).assume_init_read());
-
-        head.next_read_idx += 1;
-
-        Some(value)
-    }
-}
-
-impl<T> Drop for Queue<T> {
-    fn drop(&mut self) {
-        unsafe {
-            // Drop all values.
-            while self.pop().is_some() {}
-
-            // All values have been dropped: the last segment can be freed.
-
-            // Safety: this is the only thread accessing the head since both the
-            // consumer and producer have been dropped.
-            let head = self.head.with_mut(|p| &mut *p);
-
-            // Safety: the pointer was initialized from a box and the segment is
-            // still allocated since we are the only thread that can deallocate
-            // it.
-            let _ = Box::from_raw(head.segment.as_ptr());
-        }
-    }
-}
-
-unsafe impl<T: Send> Send for Queue<T> {}
-unsafe impl<T: Send> Sync for Queue<T> {}
-
-impl<T> UnwindSafe for Queue<T> {}
-impl<T> RefUnwindSafe for Queue<T> {}
-
-/// A handle to a single-producer, single-consumer queue that can push values.
-pub(crate) struct Producer<T> {
-    queue: Arc<Queue<T>>,
-    _non_sync_phantom: PhantomData<Cell<()>>,
-}
-impl<T> Producer<T> {
-    /// Pushes a value to the queue.
-    pub(crate) fn push(&self, value: T) -> Result<(), PushError> {
-        if Arc::strong_count(&self.queue) == 1 {
-            return Err(PushError {});
-        }
-
-        unsafe { self.queue.push(value) };
-
-        Ok(())
-    }
-}
-
-#[derive(Debug, PartialEq, Eq, Clone, Copy)]
-/// Error returned when a push failed due to the consumer being dropped.
-pub(crate) struct PushError {}
-
-impl fmt::Display for PushError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "sending message into a closed mailbox")
-    }
-}
-
-impl Error for PushError {}
-
-/// A handle to a single-producer, single-consumer queue that can pop values.
-pub(crate) struct Consumer<T> {
-    queue: Arc<Queue<T>>,
-    _non_sync_phantom: PhantomData<Cell<()>>,
-}
-impl<T> Consumer<T> {
-    /// Pops a value from the queue.
-    pub(crate) fn pop(&self) -> Option<T> {
-        unsafe { self.queue.pop() }
-    }
-}
-
-/// Creates the producer and consumer handles of a single-producer,
-/// single-consumer queue.
-pub(crate) fn spsc_queue<T>() -> (Producer<T>, Consumer<T>) {
-    let queue = Arc::new(Queue::new());
-
-    let producer = Producer {
-        queue: queue.clone(),
-        _non_sync_phantom: PhantomData,
-    };
-    let consumer = Consumer {
-        queue,
-        _non_sync_phantom: PhantomData,
-    };
-
-    (producer, consumer)
-}
-
-/// Loom tests.
-#[cfg(all(test, not(asynchronix_loom)))]
-mod tests {
-    use super::*;
-
-    use std::thread;
-
-    #[test]
-    fn spsc_queue_basic() {
-        const VALUE_COUNT: usize = if cfg!(miri) { 1000 } else { 100_000 };
-
-        let (producer, consumer) = spsc_queue();
-
-        let th = thread::spawn(move || {
-            for i in 0..VALUE_COUNT {
-                let value = loop {
-                    if let Some(v) = consumer.pop() {
-                        break v;
-                    }
-                };
-
-                assert_eq!(value, i);
-            }
-        });
-
-        for i in 0..VALUE_COUNT {
-            producer.push(i).unwrap();
-        }
-
-        th.join().unwrap();
-    }
-}
-
-/// Loom tests.
-#[cfg(all(test, asynchronix_loom))]
-mod tests {
-    use super::*;
-
-    use loom::model::Builder;
-    use loom::thread;
-
-    #[test]
-    fn loom_spsc_queue_basic() {
-        const DEFAULT_PREEMPTION_BOUND: usize = 4;
-        const VALUE_COUNT: usize = 10;
-
-        let mut builder = Builder::new();
-        if builder.preemption_bound.is_none() {
-            builder.preemption_bound = Some(DEFAULT_PREEMPTION_BOUND);
-        }
-
-        builder.check(move || {
-            let (producer, consumer) = spsc_queue();
-
-            let th = thread::spawn(move || {
-                let mut value = 0;
-                for _ in 0..VALUE_COUNT {
-                    if let Some(v) = consumer.pop() {
-                        assert_eq!(v, value);
-                        value += 1;
-                    }
-                }
-            });
-
-            for i in 0..VALUE_COUNT {
-                let _ = producer.push(i);
-            }
-
-            th.join().unwrap();
-        });
-    }
-
-    #[test]
-    fn loom_spsc_queue_new_segment() {
-        const DEFAULT_PREEMPTION_BOUND: usize = 4;
-        const VALUE_COUNT_BEFORE: usize = 5;
-        const VALUE_COUNT_AFTER: usize = 5;
-
-        let mut builder = Builder::new();
-        if builder.preemption_bound.is_none() {
-            builder.preemption_bound = Some(DEFAULT_PREEMPTION_BOUND);
-        }
-
-        builder.check(move || {
-            let (producer, consumer) = spsc_queue();
-
-            // Fill up the first segment except for the last `VALUE_COUNT_BEFORE` slots.
-            for i in 0..(SEGMENT_LEN - VALUE_COUNT_BEFORE) {
-                producer.push(i).unwrap();
-                consumer.pop();
-            }
-
-            let th = thread::spawn(move || {
-                let mut value = SEGMENT_LEN - VALUE_COUNT_BEFORE;
-                for _ in (SEGMENT_LEN - VALUE_COUNT_BEFORE)..(SEGMENT_LEN + VALUE_COUNT_AFTER) {
-                    if let Some(v) = consumer.pop() {
-                        assert_eq!(v, value);
-                        value += 1;
-                    }
-                }
-            });
-
-            for i in (SEGMENT_LEN - VALUE_COUNT_BEFORE)..(SEGMENT_LEN + VALUE_COUNT_AFTER) {
-                let _ = producer.push(i);
-            }
-
-            th.join().unwrap();
-        });
-    }
-}

asynchronix/tests/model_scheduling.rs

@@ -1,225 +0,0 @@
-//! Event scheduling within `Model` input methods.
-
-use std::time::Duration;
-
-use asynchronix::model::{Model, Output};
-use asynchronix::simulation::{Mailbox, SimInit};
-use asynchronix::time::{EventKey, MonotonicTime, Scheduler};
-
-#[test]
-fn model_schedule_event() {
-    #[derive(Default)]
-    struct TestModel {
-        output: Output<()>,
-    }
-    impl TestModel {
-        fn trigger(&mut self, _: (), scheduler: &Scheduler<Self>) {
-            scheduler
-                .schedule_event(scheduler.time() + Duration::from_secs(2), Self::action, ())
-                .unwrap();
-        }
-        async fn action(&mut self) {
-            self.output.send(()).await;
-        }
-    }
-    impl Model for TestModel {}
-
-    let mut model = TestModel::default();
-    let mbox = Mailbox::new();
-
-    let mut output = model.output.connect_stream().0;
-    let addr = mbox.address();
-
-    let t0 = MonotonicTime::EPOCH;
-    let mut simu = SimInit::new().add_model(model, mbox).init(t0);
-
-    simu.send_event(TestModel::trigger, (), addr);
-    simu.step();
-    assert_eq!(simu.time(), t0 + Duration::from_secs(2));
-    assert!(output.next().is_some());
-    simu.step();
-    assert!(output.next().is_none());
-}
-
-#[test]
-fn model_cancel_future_keyed_event() {
-    #[derive(Default)]
-    struct TestModel {
-        output: Output<i32>,
-        key: Option<EventKey>,
-    }
-    impl TestModel {
-        fn trigger(&mut self, _: (), scheduler: &Scheduler<Self>) {
-            scheduler
-                .schedule_event(scheduler.time() + Duration::from_secs(1), Self::action1, ())
-                .unwrap();
-            self.key = scheduler
-                .schedule_keyed_event(scheduler.time() + Duration::from_secs(2), Self::action2, ())
-                .ok();
-        }
-        async fn action1(&mut self) {
-            self.output.send(1).await;
-            // Cancel the call to `action2`.
-            self.key.take().unwrap().cancel();
-        }
-        async fn action2(&mut self) {
-            self.output.send(2).await;
-        }
-    }
-    impl Model for TestModel {}
-
-    let mut model = TestModel::default();
-    let mbox = Mailbox::new();
-
-    let mut output = model.output.connect_stream().0;
-    let addr = mbox.address();
-
-    let t0 = MonotonicTime::EPOCH;
-    let mut simu = SimInit::new().add_model(model, mbox).init(t0);
-
-    simu.send_event(TestModel::trigger, (), addr);
-    simu.step();
-    assert_eq!(simu.time(), t0 + Duration::from_secs(1));
-    assert_eq!(output.next(), Some(1));
-    simu.step();
-    assert_eq!(simu.time(), t0 + Duration::from_secs(1));
-    assert!(output.next().is_none());
-}
-
-#[test]
-fn model_cancel_same_time_keyed_event() {
-    #[derive(Default)]
-    struct TestModel {
-        output: Output<i32>,
-        key: Option<EventKey>,
-    }
-    impl TestModel {
-        fn trigger(&mut self, _: (), scheduler: &Scheduler<Self>) {
-            scheduler
-                .schedule_event(scheduler.time() + Duration::from_secs(2), Self::action1, ())
-                .unwrap();
-            self.key = scheduler
-                .schedule_keyed_event(scheduler.time() + Duration::from_secs(2), Self::action2, ())
-                .ok();
-        }
-        async fn action1(&mut self) {
-            self.output.send(1).await;
-            // Cancel the call to `action2`.
-            self.key.take().unwrap().cancel();
-        }
-        async fn action2(&mut self) {
-            self.output.send(2).await;
-        }
-    }
-    impl Model for TestModel {}
-
-    let mut model = TestModel::default();
-    let mbox = Mailbox::new();
-
-    let mut output = model.output.connect_stream().0;
-    let addr = mbox.address();
-
-    let t0 = MonotonicTime::EPOCH;
-    let mut simu = SimInit::new().add_model(model, mbox).init(t0);
-
-    simu.send_event(TestModel::trigger, (), addr);
-    simu.step();
-    assert_eq!(simu.time(), t0 + Duration::from_secs(2));
-    assert_eq!(output.next(), Some(1));
-    assert!(output.next().is_none());
-    simu.step();
-    assert!(output.next().is_none());
-}
-
-#[test]
-fn model_schedule_periodic_event() {
-    #[derive(Default)]
-    struct TestModel {
-        output: Output<i32>,
-    }
-    impl TestModel {
-        fn trigger(&mut self, _: (), scheduler: &Scheduler<Self>) {
-            scheduler
-                .schedule_periodic_event(
-                    scheduler.time() + Duration::from_secs(2),
-                    Duration::from_secs(3),
-                    Self::action,
-                    42,
-                )
-                .unwrap();
-        }
-        async fn action(&mut self, payload: i32) {
-            self.output.send(payload).await;
-        }
-    }
-    impl Model for TestModel {}
-
-    let mut model = TestModel::default();
-    let mbox = Mailbox::new();
-
-    let mut output = model.output.connect_stream().0;
-    let addr = mbox.address();
-
-    let t0 = MonotonicTime::EPOCH;
-    let mut simu = SimInit::new().add_model(model, mbox).init(t0);
-
-    simu.send_event(TestModel::trigger, (), addr);
-
-    // Move to the next events at t0 + 2s + k*3s.
-    for k in 0..10 {
-        simu.step();
-        assert_eq!(
-            simu.time(),
-            t0 + Duration::from_secs(2) + k * Duration::from_secs(3)
-        );
-        assert_eq!(output.next(), Some(42));
-        assert!(output.next().is_none());
-    }
-}
-
-#[test]
-fn model_cancel_periodic_event() {
-    #[derive(Default)]
-    struct TestModel {
-        output: Output<()>,
-        key: Option<EventKey>,
-    }
-    impl TestModel {
-        fn trigger(&mut self, _: (), scheduler: &Scheduler<Self>) {
-            self.key = scheduler
-                .schedule_keyed_periodic_event(
-                    scheduler.time() + Duration::from_secs(2),
-                    Duration::from_secs(3),
-                    Self::action,
-                    (),
-                )
-                .ok();
-        }
-        async fn action(&mut self) {
-            self.output.send(()).await;
-            // Cancel the next events.
-            self.key.take().unwrap().cancel();
-        }
-    }
-    impl Model for TestModel {}
-
-    let mut model = TestModel::default();
-    let mbox = Mailbox::new();
-
-    let mut output = model.output.connect_stream().0;
-    let addr = mbox.address();
-
-    let t0 = MonotonicTime::EPOCH;
-    let mut simu = SimInit::new().add_model(model, mbox).init(t0);
-
-    simu.send_event(TestModel::trigger, (), addr);
-
-    simu.step();
-    assert_eq!(simu.time(), t0 + Duration::from_secs(2));
-    assert!(output.next().is_some());
-    assert!(output.next().is_none());
-
-    simu.step();
-    assert_eq!(simu.time(), t0 + Duration::from_secs(2));
-    assert!(output.next().is_none());
-}

asynchronix/tests/tests.rs

@@ -1,4 +0,0 @@
-#[cfg(not(asynchronix_loom))]
-mod model_scheduling;
-#[cfg(not(asynchronix_loom))]
-mod simulation_scheduling;

nexosim-util/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "nexosim-util"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+nexosim = { version = "0.3.1", path = "../nexosim" }
+
+[dev-dependencies]
+rand = "0.8"

nexosim-util/README.md

@@ -0,0 +1,5 @@
+# Utilities for model-building
+
+This crate contains utilities used for model and simulation bench development.
+
+

nexosim-util/examples/observables.rs

@@ -0,0 +1,304 @@
+//! Example: processor with observable states.
+//!
+//! This example demonstrates in particular:
+//!
+//! * the use of observable states,
+//! * state machine with delays.
+//!
+//! ```text
+//!                     ┌───────────┐
+//! Switch ON/OFF ●────►│           ├────► Mode
+//!                     │ Processor │
+//! Process data  ●────►│           ├────► Value
+//!                     │           │
+//!                     │           ├────► House Keeping
+//!                     └───────────┘
+//! ```
+
+use std::time::Duration;
+
+use nexosim::model::{Context, InitializedModel, Model};
+use nexosim::ports::{EventBuffer, Output};
+use nexosim::simulation::{AutoActionKey, Mailbox, SimInit, SimulationError};
+use nexosim::time::MonotonicTime;
+use nexosim_util::observables::{Observable, ObservableState, ObservableValue};
+
+/// House keeping TM.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct Hk {
+    pub voltage: f64,
+    pub current: f64,
+}
+
+impl Default for Hk {
+    fn default() -> Self {
+        Self {
+            voltage: 0.0,
+            current: 0.0,
+        }
+    }
+}
+
+/// Processor mode ID.
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
+pub enum ModeId {
+    #[default]
+    Off,
+    Idle,
+    Processing,
+}
+
+/// Processor state.
+#[derive(Default)]
+pub enum State {
+    #[default]
+    Off,
+    Idle,
+    Processing(AutoActionKey),
+}
+
+impl Observable<ModeId> for State {
+    fn observe(&self) -> ModeId {
+        match *self {
+            State::Off => ModeId::Off,
+            State::Idle => ModeId::Idle,
+            State::Processing(_) => ModeId::Processing,
+        }
+    }
+}
+
+/// Processor model.
+pub struct Processor {
+    /// Mode output.
+    pub mode: Output<ModeId>,
+
+    /// Calculated value output.
+    pub value: Output<u16>,
+
+    /// HK output.
+    pub hk: Output<Hk>,
+
+    /// Internal state.
+    state: ObservableState<State, ModeId>,
+
+    /// Accumulator.
+    acc: ObservableValue<u16>,
+
+    /// Electrical data.
+    elc: ObservableValue<Hk>,
+}
+
+impl Processor {
+    /// Create a new processor.
+    pub fn new() -> Self {
+        let mode = Output::new();
+        let value = Output::new();
+        let hk = Output::new();
+        Self {
+            mode: mode.clone(),
+            value: value.clone(),
+            hk: hk.clone(),
+            state: ObservableState::new(mode),
+            acc: ObservableValue::new(value),
+            elc: ObservableValue::new(hk),
+        }
+    }
+
+    /// Switch processor ON/OFF.
+    pub async fn switch_power(&mut self, on: bool) {
+        if on {
+            self.state.set(State::Idle).await;
+            self.elc
+                .set(Hk {
+                    voltage: 5.5,
+                    current: 0.1,
+                })
+                .await;
+            self.acc.set(0).await;
+        } else {
+            self.state.set(State::Off).await;
+            self.elc.set(Hk::default()).await;
+            self.acc.set(0).await;
+        }
+    }
+
+    /// Process data for dt milliseconds.
+    pub async fn process(&mut self, dt: u64, cx: &mut Context<Self>) {
+        if matches!(self.state.observe(), ModeId::Idle | ModeId::Processing) {
+            self.state
+                .set(State::Processing(
+                    cx.schedule_keyed_event(Duration::from_millis(dt), Self::finish_processing, ())
+                        .unwrap()
+                        .into_auto(),
+                ))
+                .await;
+            self.elc.modify(|hk| hk.current = 1.0).await;
+        }
+    }
+
+    /// Finish processing.
+    async fn finish_processing(&mut self) {
+        self.state.set(State::Idle).await;
+        self.acc.modify(|a| *a += 1).await;
+        self.elc.modify(|hk| hk.current = 0.1).await;
+    }
+}
+
+impl Model for Processor {
+    /// Propagate all internal states.
+    async fn init(mut self, _: &mut Context<Self>) -> InitializedModel<Self> {
+        self.state.propagate().await;
+        self.acc.propagate().await;
+        self.elc.propagate().await;
+        self.into()
+    }
+}
+
+fn main() -> Result<(), SimulationError> {
+    // ---------------
+    // Bench assembly.
+    // ---------------
+
+    // Models.
+    let mut proc = Processor::new();
+
+    // Mailboxes.
+    let proc_mbox = Mailbox::new();
+
+    // Model handles for simulation.
+    let mut mode = EventBuffer::new();
+    let mut value = EventBuffer::new();
+    let mut hk = EventBuffer::new();
+
+    proc.mode.connect_sink(&mode);
+    proc.value.connect_sink(&value);
+    proc.hk.connect_sink(&hk);
+    let proc_addr = proc_mbox.address();
+
+    // Start time (arbitrary since models do not depend on absolute time).
+    let t0 = MonotonicTime::EPOCH;
+
+    // Assembly and initialization.
+    let mut simu = SimInit::new()
+        .add_model(proc, proc_mbox, "proc")
+        .init(t0)?
+        .0;
+
+    // ----------
+    // Simulation.
+    // ----------
+
+    // Initial state.
+    expect(
+        &mut mode,
+        Some(ModeId::Off),
+        &mut value,
+        Some(0),
+        &mut hk,
+        0.0,
+        0.0,
+    );
+
+    // Switch processor on.
+    simu.process_event(Processor::switch_power, true, &proc_addr)?;
+    expect(
+        &mut mode,
+        Some(ModeId::Idle),
+        &mut value,
+        Some(0),
+        &mut hk,
+        5.5,
+        0.1,
+    );
+
+    // Trigger processing.
+    simu.process_event(Processor::process, 100, &proc_addr)?;
+    expect(
+        &mut mode,
+        Some(ModeId::Processing),
+        &mut value,
+        None,
+        &mut hk,
+        5.5,
+        1.0,
+    );
+
+    // All data processed.
+    simu.step_until(Duration::from_millis(101))?;
+    expect(
+        &mut mode,
+        Some(ModeId::Idle),
+        &mut value,
+        Some(1),
+        &mut hk,
+        5.5,
+        0.1,
+    );
+
+    // Trigger long processing.
+    simu.process_event(Processor::process, 100, &proc_addr)?;
+    expect(
+        &mut mode,
+        Some(ModeId::Processing),
+        &mut value,
+        None,
+        &mut hk,
+        5.5,
+        1.0,
+    );
+
+    // Trigger short processing, it cancels the previous one.
+    simu.process_event(Processor::process, 10, &proc_addr)?;
+    expect(
+        &mut mode,
+        Some(ModeId::Processing),
+        &mut value,
+        None,
+        &mut hk,
+        5.5,
+        1.0,
+    );
+
+    // Wait for short processing to finish, check results.
+    simu.step_until(Duration::from_millis(11))?;
+    expect(
+        &mut mode,
+        Some(ModeId::Idle),
+        &mut value,
+        Some(2),
+        &mut hk,
+        5.5,
+        0.1,
+    );
+
+    // Wait long enough, no state change as the long processing has been
+    // cancelled.
+    simu.step_until(Duration::from_millis(100))?;
+    assert_eq!(mode.next(), None);
+    assert_eq!(value.next(), None);
+    assert_eq!(hk.next(), None);
+
+    Ok(())
+}
+
+// Check observable state.
+fn expect(
+    mode: &mut EventBuffer<ModeId>,
+    mode_ex: Option<ModeId>,
+    value: &mut EventBuffer<u16>,
+    value_ex: Option<u16>,
+    hk: &mut EventBuffer<Hk>,
+    voltage_ex: f64,
+    current_ex: f64,
+) {
+    assert_eq!(mode.next(), mode_ex);
+    assert_eq!(value.next(), value_ex);
+    let hk_value = hk.next().unwrap();
+    assert!(same(hk_value.voltage, voltage_ex));
+    assert!(same(hk_value.current, current_ex));
+}
+
+// Compare two voltages or currents.
+fn same(a: f64, b: f64) -> bool {
+    (a - b).abs() < 1e-12
+}

nexosim-util/examples/replier_adaptor.rs

@@ -0,0 +1,276 @@
+//! Example: RIU acquiring data from sensor.
+//!
+//! This example demonstrates in particular:
+//!
+//! * the use of replier port adaptor,
+//! * periodic model self-scheduling.
+//!
+//! ```text
+//!                       ┌────────┐                ┌─────────┐  Sensor TC  ┌─────┐
+//! Set temperature ●────►│        │  ◄Sensor TC    │         │◄────────────┤     │
+//!                       │ Sensor │◄►────────────►◄│ Adaptor │  Sensor TM  │ RIU ├────► RIU TM
+//! Set illuminance ●────►│        │   Sensor TM►   │         ├────────────►│     │
+//!                       └────────┘                └─────────┘             └─────┘
+//! ```
+
+use std::fmt::Debug;
+use std::time::Duration;
+
+use nexosim::model::{Context, InitializedModel, Model};
+use nexosim::ports::{EventBuffer, Output};
+use nexosim::simulation::{Mailbox, SimInit, SimulationError};
+use nexosim::time::MonotonicTime;
+use nexosim_util::combinators::ReplierAdaptor;
+
+const DELTA: Duration = Duration::from_millis(2);
+const PERIOD: Duration = Duration::from_secs(1);
+
+/// Sensor TC.
+#[derive(Clone, Debug, PartialEq)]
+pub enum SensorTc {
+    GetTemp,
+    GetIllum,
+}
+
+/// Sensor TM.
+#[derive(Clone, Debug, PartialEq)]
+pub enum SensorTm {
+    Temp(f64),
+    Illum(f64),
+}
+
+/// Sensor model.
+pub struct Sensor {
+    /// Temperature [deg C] -- internal state.
+    temp: f64,
+
+    /// Illuminance [lx] -- internal state.
+    illum: f64,
+}
+
+impl Sensor {
+    /// Creates a sensor model.
+    pub fn new() -> Self {
+        Self {
+            temp: 0.0,
+            illum: 0.0,
+        }
+    }
+
+    /// Sets sensor temperature [deg C].
+    pub async fn set_temp(&mut self, temp: f64) {
+        self.temp = temp;
+    }
+
+    /// Sets sensor illuminance [lx].
+    pub async fn set_illum(&mut self, illum: f64) {
+        self.illum = illum;
+    }
+
+    /// Processes sensor TC -- input port.
+    pub async fn process_tc(&mut self, tc: SensorTc) -> SensorTm {
+        match tc {
+            SensorTc::GetTemp => SensorTm::Temp(self.temp),
+            SensorTc::GetIllum => SensorTm::Illum(self.illum),
+        }
+    }
+}
+
+impl Model for Sensor {}
+
+/// Internal TM field.
+#[derive(Clone, Debug, PartialEq)]
+pub struct TmField<T>
+where
+    T: Clone + Debug + PartialEq,
+{
+    /// TM value.
+    pub value: T,
+
+    /// TM readiness flag.
+    pub ready: bool,
+}
+
+/// RIU TM.
+#[derive(Clone, Debug, PartialEq)]
+pub struct RiuTm {
+    /// Temperature [deg C].
+    temp: f64,
+
+    /// Iluminance [lx].
+    illum: f64,
+}
+
+/// RIU model.
+pub struct Riu {
+    /// Sensor TC -- output port.
+    pub sensor_tc: Output<SensorTc>,
+
+    /// RIU TM -- output port.
+    pub tm: Output<RiuTm>,
+
+    /// Temperature [deg C] -- internal state.
+    temp: TmField<f64>,
+
+    /// Illuminance [lx] -- internal state.
+    illum: TmField<f64>,
+}
+
+impl Riu {
+    /// Creates an RIU model.
+    pub fn new() -> Self {
+        Self {
+            sensor_tc: Output::new(),
+            tm: Output::new(),
+            temp: TmField {
+                value: 0.0,
+                ready: true,
+            },
+            illum: TmField {
+                value: 0.0,
+                ready: true,
+            },
+        }
+    }
+
+    /// Processes sensor TM -- input port.
+    pub async fn sensor_tm(&mut self, tm: SensorTm) {
+        match tm {
+            SensorTm::Temp(temp) => {
+                self.temp = TmField {
+                    value: temp,
+                    ready: true,
+                }
+            }
+            SensorTm::Illum(illum) => {
+                self.illum = TmField {
+                    value: illum,
+                    ready: true,
+                }
+            }
+        }
+
+        if self.temp.ready && self.illum.ready {
+            self.report().await
+        }
+    }
+
+    /// Starts sensor TM acquisition -- periodic activity.
+    async fn acquire(&mut self) {
+        self.temp.ready = false;
+        self.illum.ready = false;
+        self.sensor_tc.send(SensorTc::GetTemp).await;
+        self.sensor_tc.send(SensorTc::GetIllum).await
+    }
+
+    /// Reports RIU TM.
+    async fn report(&mut self) {
+        self.tm
+            .send(RiuTm {
+                temp: self.temp.value,
+                illum: self.illum.value,
+            })
+            .await
+    }
+}
+
+impl Model for Riu {
+    /// Initializes model.
+    async fn init(self, cx: &mut Context<Self>) -> InitializedModel<Self> {
+        // Schedule periodic acquisition.
+        cx.schedule_periodic_event(DELTA, PERIOD, Riu::acquire, ())
+            .unwrap();
+
+        self.into()
+    }
+}
+
+fn main() -> Result<(), SimulationError> {
+    // ---------------
+    // Bench assembly.
+    // ---------------
+
+    // Models.
+    let sensor = Sensor::new();
+    let mut riu = Riu::new();
+    let mut sensor_adaptor = ReplierAdaptor::new();
+
+    // Mailboxes.
+    let sensor_mbox = Mailbox::new();
+    let riu_mbox = Mailbox::new();
+    let sensor_adaptor_mbox = Mailbox::new();
+
+    // Connections.
+    riu.sensor_tc
+        .connect(ReplierAdaptor::input, &sensor_adaptor_mbox);
+    sensor_adaptor.output.connect(Riu::sensor_tm, &riu_mbox);
+    sensor_adaptor
+        .requestor
+        .connect(Sensor::process_tc, &sensor_mbox);
+
+    // Model handles for simulation.
+    let mut tm = EventBuffer::new();
+    let sensor_addr = sensor_mbox.address();
+
+    riu.tm.connect_sink(&tm);
+
+    // Start time (arbitrary since models do not depend on absolute time).
+    let t0 = MonotonicTime::EPOCH;
+
+    // Assembly and initialization.
+    let mut simu = SimInit::new()
+        .add_model(sensor, sensor_mbox, "sensor")
+        .add_model(riu, riu_mbox, "riu")
+        .add_model(sensor_adaptor, sensor_adaptor_mbox, "sensor_adaptor")
+        .init(t0)?
+        .0;
+
+    // ----------
+    // Simulation.
+    // ----------
+
+    // Initial state: no RIU TM.
+    assert_eq!(tm.next(), None);
+
+    simu.step_until(Duration::from_millis(1200))?;
+
+    // RIU TM generated.
+    assert_eq!(
+        tm.next(),
+        Some(RiuTm {
+            temp: 0.0,
+            illum: 0.0
+        })
+    );
+
+    // Consume all RIU TM generated so far.
+    while tm.next().is_some() {}
+
+    // Set temperature and wait for RIU TM.
+    simu.process_event(Sensor::set_temp, 2.0, &sensor_addr)?;
+
+    simu.step_until(Duration::from_millis(1000))?;
+
+    assert_eq!(
+        tm.next(),
+        Some(RiuTm {
+            temp: 2.0,
+            illum: 0.0
+        })
+    );
+
+    // Set illuminance and wait for RIU TM.
+    simu.process_event(Sensor::set_illum, 3.0, &sensor_addr)?;
+
+    simu.step_until(Duration::from_millis(1000))?;
+
+    assert_eq!(
+        tm.next(),
+        Some(RiuTm {
+            temp: 2.0,
+            illum: 3.0
+        })
+    );
+
+    Ok(())
+}

nexosim-util/examples/simulation_driven.rs

@@ -0,0 +1,274 @@
+//! Example: a simulation that runs infinitely until stopped. This setup is
+//! typical for hardware-in-the-loop use case. The test scenario is driven by
+//! simulation events.
+//!
+//! This example demonstrates in particular:
+//!
+//! * infinite simulation,
+//! * blocking event queue,
+//! * simulation halting,
+//! * system clock,
+//! * periodic scheduling,
+//! * observable state.
+//!
+//! ```text
+//! ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+//! ┃ Simulation                             ┃
+//! ┃   ┌──────────┐       ┌──────────┐mode  ┃
+//! ┃   │          │pulses │          ├──────╂┐BlockingEventQueue
+//! ┃   │ Detector ├──────►│ Counter  │count ┃├───────────────────►
+//! ┃   │          │       │          ├──────╂┘
+//! ┃   └──────────┘       └──────────┘      ┃
+//! ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+//! ```
+
+use std::future::Future;
+use std::thread;
+use std::time::Duration;
+
+use rand::Rng;
+
+use nexosim::model::{Context, Model};
+use nexosim::ports::{BlockingEventQueue, Output};
+use nexosim::simulation::{ActionKey, ExecutionError, Mailbox, SimInit, SimulationError};
+use nexosim::time::{AutoSystemClock, MonotonicTime};
+use nexosim_util::helper_models::Ticker;
+use nexosim_util::observables::ObservableValue;
+
+const SWITCH_ON_DELAY: Duration = Duration::from_secs(1);
+const MAX_PULSE_PERIOD: u64 = 100;
+const TICK: Duration = Duration::from_millis(100);
+const N: u64 = 10;
+
+/// Counter mode.
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
+pub enum Mode {
+    #[default]
+    Off,
+    On,
+}
+
+/// Simulation event.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum Event {
+    Mode(Mode),
+    Count(u64),
+}
+
+/// The `Counter` Model.
+pub struct Counter {
+    /// Operation mode.
+    pub mode: Output<Mode>,
+
+    /// Pulses count.
+    pub count: Output<u64>,
+
+    /// Internal state.
+    state: ObservableValue<Mode>,
+
+    /// Counter.
+    acc: ObservableValue<u64>,
+}
+
+impl Counter {
+    /// Creates a new `Counter` model.
+    fn new() -> Self {
+        let mode = Output::default();
+        let count = Output::default();
+        Self {
+            mode: mode.clone(),
+            count: count.clone(),
+            state: ObservableValue::new(mode),
+            acc: ObservableValue::new(count),
+        }
+    }
+
+    /// Power -- input port.
+    pub async fn power_in(&mut self, on: bool, cx: &mut Context<Self>) {
+        match *self.state {
+            Mode::Off if on => cx
+                .schedule_event(SWITCH_ON_DELAY, Self::switch_on, ())
+                .unwrap(),
+            Mode::On if !on => self.switch_off().await,
+            _ => (),
+        };
+    }
+
+    /// Pulse -- input port.
+    pub async fn pulse(&mut self) {
+        self.acc.modify(|x| *x += 1).await;
+    }
+
+    /// Switches `Counter` on.
+    async fn switch_on(&mut self) {
+        self.state.set(Mode::On).await;
+    }
+
+    /// Switches `Counter` off.
+    async fn switch_off(&mut self) {
+        self.state.set(Mode::Off).await;
+    }
+}
+
+impl Model for Counter {}
+
+/// Detector model that produces pulses.
+pub struct Detector {
+    /// Output pulse.
+    pub pulse: Output<()>,
+
+    /// `ActionKey` of the next scheduled detection.
+    next: Option<ActionKey>,
+}
+
+impl Detector {
+    /// Creates a new `Detector` model.
+    pub fn new() -> Self {
+        Self {
+            pulse: Output::default(),
+            next: None,
+        }
+    }
+
+    /// Switches `Detector` on -- input port.
+    pub async fn switch_on(&mut self, _: (), cx: &mut Context<Self>) {
+        self.schedule_next(cx).await;
+    }
+
+    /// Switches `Detector` off -- input port.
+    pub async fn switch_off(&mut self) {
+        self.next = None;
+    }
+
+    /// Generates a pulse.
+    ///
+    /// Note: self-scheduling async methods must be for now defined with an
+    /// explicit signature instead of `async fn` due to a rustc issue.
+    fn pulse<'a>(
+        &'a mut self,
+        _: (),
+        cx: &'a mut Context<Self>,
+    ) -> impl Future<Output = ()> + Send + 'a {
+        async move {
+            self.pulse.send(()).await;
+            self.schedule_next(cx).await;
+        }
+    }
+
+    /// Schedules the next detection.
+    async fn schedule_next(&mut self, cx: &mut Context<Self>) {
+        let next = {
+            let mut rng = rand::thread_rng();
+            rng.gen_range(1..MAX_PULSE_PERIOD)
+        };
+        self.next = Some(
+            cx.schedule_keyed_event(Duration::from_millis(next), Self::pulse, ())
+                .unwrap(),
+        );
+    }
+}
+
+impl Model for Detector {}
+
+fn main() -> Result<(), SimulationError> {
+    // ---------------
+    // Bench assembly.
+    // ---------------
+
+    // Models.
+
+    // The detector model that produces pulses.
+    let mut detector = Detector::new();
+
+    // The counter model.
+    let mut counter = Counter::new();
+
+    // The ticker model that keeps simulation alive.
+    let ticker = Ticker::new(TICK);
+
+    // Mailboxes.
+    let detector_mbox = Mailbox::new();
+    let counter_mbox = Mailbox::new();
+    let ticker_mbox = Mailbox::new();
+
+    // Connections.
+    detector.pulse.connect(Counter::pulse, &counter_mbox);
+
+    // Model handles for simulation.
+    let detector_addr = detector_mbox.address();
+    let counter_addr = counter_mbox.address();
+    let observer = BlockingEventQueue::new();
+    counter
+        .mode
+        .map_connect_sink(|m| Event::Mode(*m), &observer);
+    counter
+        .count
+        .map_connect_sink(|c| Event::Count(*c), &observer);
+    let mut observer = observer.into_reader();
+
+    // Start time (arbitrary since models do not depend on absolute time).
+    let t0 = MonotonicTime::EPOCH;
+
+    // Assembly and initialization.
+    let (mut simu, mut scheduler) = SimInit::new()
+        .add_model(detector, detector_mbox, "detector")
+        .add_model(counter, counter_mbox, "counter")
+        .add_model(ticker, ticker_mbox, "ticker")
+        .set_clock(AutoSystemClock::new())
+        .init(t0)?;
+
+    // Simulation thread.
+    let simulation_handle = thread::spawn(move || {
+        // ---------- Simulation.  ----------
+        // Infinitely kept alive by the ticker model until halted.
+        simu.step_unbounded()
+    });
+
+    // Switch the counter on.
+    scheduler.schedule_event(
+        Duration::from_millis(1),
+        Counter::power_in,
+        true,
+        counter_addr,
+    )?;
+
+    // Wait until counter mode is `On`.
+    loop {
+        let event = observer.next();
+        match event {
+            Some(Event::Mode(Mode::On)) => {
+                break;
+            }
+            None => panic!("Simulation exited unexpectedly"),
+            _ => (),
+        }
+    }
+
+    // Switch the detector on.
+    scheduler.schedule_event(
+        Duration::from_millis(100),
+        Detector::switch_on,
+        (),
+        detector_addr,
+    )?;
+
+    // Wait until `N` detections.
+    loop {
+        let event = observer.next();
+        match event {
+            Some(Event::Count(c)) if c >= N => {
+                break;
+            }
+            None => panic!("Simulation exited unexpectedly"),
+            _ => (),
+        }
+    }
+
+    // Stop the simulation.
+    scheduler.halt();
+    match simulation_handle.join().unwrap() {
+        Err(ExecutionError::Halted) => Ok(()),
+        Err(e) => Err(e.into()),
+        _ => Ok(()),
+    }
+}

nexosim-util/examples/uni_requestor.rs

@@ -0,0 +1,174 @@
+//! Example: sensor reading data from environment model.
+//!
+//! This example demonstrates in particular:
+//!
+//! * cyclical self-scheduling methods,
+//! * model initialization,
+//! * simulation monitoring with buffered event sinks,
+//! * connection with mapping,
+//! * UniRequestor port.
+//!
+//! ```text
+//!                        ┌─────────────┐               ┌──────────┐
+//!                        │             │ temperature   │          │ overheat
+//! Temperature ●─────────►│ Environment ├──────────────►│  Sensor  ├──────────►
+//!                        │             │               │          │
+//!                        └─────────────┘               └──────────┘
+//! ```
+
+use std::time::Duration;
+
+use nexosim_util::observables::ObservableValue;
+
+use nexosim::model::{Context, InitializedModel, Model};
+use nexosim::ports::{EventBuffer, Output, UniRequestor};
+use nexosim::simulation::{Mailbox, SimInit, SimulationError};
+use nexosim::time::MonotonicTime;
+
+/// Sensor model
+pub struct Sensor {
+    /// Temperature [deg C] -- requestor port.
+    pub temp: UniRequestor<(), f64>,
+
+    /// Overheat detection [-] -- output port.
+    pub overheat: Output<bool>,
+
+    /// Temperature threshold [deg C] -- parameter.
+    threshold: f64,
+
+    /// Overheat detection [-] -- observable state.
+    oh: ObservableValue<bool>,
+}
+
+impl Sensor {
+    /// Creates new Sensor with overheat threshold set [deg C].
+    pub fn new(threshold: f64, temp: UniRequestor<(), f64>) -> Self {
+        let overheat = Output::new();
+        Self {
+            temp,
+            overheat: overheat.clone(),
+            threshold,
+            oh: ObservableValue::new(overheat),
+        }
+    }
+
+    /// Cyclically scheduled method that reads data from environment and
+    /// avaluates overheat state.
+    pub async fn tick(&mut self) {
+        let temp = self.temp.send(()).await.unwrap();
+        if temp > self.threshold {
+            if !self.oh.get() {
+                self.oh.set(true).await;
+            }
+        } else if *self.oh.get() {
+            self.oh.set(false).await;
+        }
+    }
+}
+
+impl Model for Sensor {
+    /// Propagate state and schedule cyclic method.
+    async fn init(mut self, context: &mut Context<Self>) -> InitializedModel<Self> {
+        self.oh.propagate().await;
+
+        context
+            .schedule_periodic_event(
+                Duration::from_millis(500),
+                Duration::from_millis(500),
+                Self::tick,
+                (),
+            )
+            .unwrap();
+
+        self.into()
+    }
+}
+
+/// Environment model.
+pub struct Env {
+    /// Temperature [deg F] -- internal state.
+    temp: f64,
+}
+
+impl Env {
+    /// Creates new environment model with the temperature [deg F] set.
+    pub fn new(temp: f64) -> Self {
+        Self { temp }
+    }
+
+    /// Sets temperature [deg F].
+    pub async fn set_temp(&mut self, temp: f64) {
+        self.temp = temp;
+    }
+
+    /// Gets temperature [deg F].
+    pub async fn get_temp(&mut self, _: ()) -> f64 {
+        self.temp
+    }
+}
+
+impl Model for Env {}
+
+/// Converts Fahrenheit to Celsius.
+pub fn fahr_to_cels(t: f64) -> f64 {
+    5.0 * (t - 32.0) / 9.0
+}
+
+fn main() -> Result<(), SimulationError> {
+    // ---------------
+    // Bench assembly.
+    // ---------------
+
+    // Mailboxes.
+    let sensor_mbox = Mailbox::new();
+    let env_mbox = Mailbox::new();
+
+    // Connect data line and convert Fahrenheit degrees to Celsius.
+    let temp_req = UniRequestor::with_map(|x| *x, fahr_to_cels, Env::get_temp, &env_mbox);
+
+    // Models.
+    let mut sensor = Sensor::new(100.0, temp_req);
+    let env = Env::new(0.0);
+
+    // Model handles for simulation.
+    let env_addr = env_mbox.address();
+
+    let mut overheat = EventBuffer::new();
+    sensor.overheat.connect_sink(&overheat);
+
+    // Start time (arbitrary since models do not depend on absolute time).
+    let t0 = MonotonicTime::EPOCH;
+
+    // Assembly and initialization.
+    let (mut simu, scheduler) = SimInit::new()
+        .add_model(sensor, sensor_mbox, "sensor")
+        .add_model(env, env_mbox, "env")
+        .init(t0)?;
+
+    // ----------
+    // Simulation.
+    // ----------
+
+    // Check initial conditions.
+    assert_eq!(simu.time(), t0);
+    assert_eq!(overheat.next(), Some(false));
+    assert!(overheat.next().is_none());
+
+    // Change temperature in 2s.
+    scheduler
+        .schedule_event(Duration::from_secs(2), Env::set_temp, 105.0, &env_addr)
+        .unwrap();
+
+    // Change temperature in 4s.
+    scheduler
+        .schedule_event(Duration::from_secs(4), Env::set_temp, 213.0, &env_addr)
+        .unwrap();
+
+    simu.step_until(Duration::from_secs(3))?;
+    assert!(overheat.next().is_none());
+
+    simu.step_until(Duration::from_secs(5))?;
+    assert_eq!(overheat.next(), Some(true));
+
+    Ok(())
+}

nexosim-util/src/combinators.rs

@@ -0,0 +1,47 @@
+//! Connector combinators.
+//!
+//! This module contains combinator types useful for simulation bench assembly.
+//!
+
+use nexosim::model::Model;
+use nexosim::ports::{Output, Requestor};
+
+/// A replier adaptor.
+///
+/// `ReplierAdaptor` generic model is aimed to connect pair of input/output
+/// ports to a replier ports.
+///
+/// Model input is propagated to all the connected replier ports and their
+/// answers are written to the model output.
+pub struct ReplierAdaptor<T: Clone + Send + 'static, R: Clone + Send + 'static> {
+    /// Requestor port to be connected to replier port.
+    pub requestor: Requestor<T, R>,
+
+    /// Output port to be connected to input port.
+    pub output: Output<R>,
+}
+
+impl<T: Clone + Send + 'static, R: Clone + Send + 'static> ReplierAdaptor<T, R> {
+    /// Creates a `ReplierAdaptor` model.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Input port.
+    pub async fn input(&mut self, data: T) {
+        for res in self.requestor.send(data).await {
+            self.output.send(res).await;
+        }
+    }
+}
+
+impl<T: Clone + Send + 'static, R: Clone + Send + 'static> Model for ReplierAdaptor<T, R> {}
+
+impl<T: Clone + Send + 'static, R: Clone + Send + 'static> Default for ReplierAdaptor<T, R> {
+    fn default() -> Self {
+        Self {
+            requestor: Requestor::new(),
+            output: Output::new(),
+        }
+    }
+}

nexosim-util/src/helper_models.rs

@@ -0,0 +1,35 @@
+//! Helper models.
+//!
+//! This module contains helper models useful for simulation bench assembly.
+//!
+
+use std::time::Duration;
+
+use nexosim::model::{Context, InitializedModel, Model};
+
+/// A ticker model.
+///
+/// This model self-schedules at the specified period, which can be used to keep
+/// the simulation alive.
+pub struct Ticker {
+    /// Tick period.
+    tick: Duration,
+}
+
+impl Ticker {
+    /// Creates a new `Ticker` with the specified self-scheduling period.
+    pub fn new(tick: Duration) -> Self {
+        Self { tick }
+    }
+
+    /// Self-scheduled function.
+    async fn tick(&mut self) {}
+}
+
+impl Model for Ticker {
+    async fn init(self, cx: &mut Context<Self>) -> InitializedModel<Self> {
+        cx.schedule_periodic_event(self.tick, self.tick, Self::tick, ())
+            .unwrap();
+        self.into()
+    }
+}

nexosim-util/src/lib.rs

@@ -0,0 +1,3 @@
+pub mod combinators;
+pub mod helper_models;
+pub mod observables;

nexosim-util/src/observables.rs

@@ -0,0 +1,96 @@
+//! Observable states.
+//!
+//! This module contains types used to implement states automatically propagated
+//! to output on change.
+//!
+
+use std::ops::Deref;
+
+use nexosim::ports::Output;
+
+/// Observability trait.
+pub trait Observable<T> {
+    /// Observe the value.
+    fn observe(&self) -> T;
+}
+
+impl<T> Observable<T> for T
+where
+    T: Clone,
+{
+    fn observe(&self) -> Self {
+        self.clone()
+    }
+}
+
+/// Observable state.
+///
+/// This object encapsulates state. Every state change access is propagated to
+/// the output.
+#[derive(Debug)]
+pub struct ObservableState<S, T>
+where
+    S: Observable<T> + Default,
+    T: Clone + Send + 'static,
+{
+    /// State.
+    state: S,
+
+    /// Output used for observation.
+    out: Output<T>,
+}
+
+impl<S, T> ObservableState<S, T>
+where
+    S: Observable<T> + Default,
+    T: Clone + Send + 'static,
+{
+    /// New default state.
+    pub fn new(out: Output<T>) -> Self {
+        Self {
+            state: S::default(),
+            out,
+        }
+    }
+
+    /// Get state.
+    pub fn get(&self) -> &S {
+        &self.state
+    }
+
+    /// Set state.
+    pub async fn set(&mut self, value: S) {
+        self.state = value;
+        self.out.send(self.state.observe()).await;
+    }
+
+    /// Modify state using mutable reference.
+    pub async fn modify<F, R>(&mut self, f: F) -> R
+    where
+        F: FnOnce(&mut S) -> R,
+    {
+        let r = f(&mut self.state);
+        self.out.send(self.state.observe()).await;
+        r
+    }
+
+    /// Propagate value.
+    pub async fn propagate(&mut self) {
+        self.out.send(self.state.observe()).await;
+    }
+}
+
+impl<S, T> Deref for ObservableState<S, T>
+where
+    S: Observable<T> + Default,
+    T: Clone + Send + 'static,
+{
+    type Target = S;
+
+    fn deref(&self) -> &S {
+        &self.state
+    }
+}
+
+/// Observable value.
+pub type ObservableValue<T> = ObservableState<T, T>;

nexosim/Cargo.toml

@@ -0,0 +1,112 @@
+[package]
+name = "nexosim"
+# When incrementing version and releasing to crates.io:
+# - Update crate version in this Cargo.toml
+# - Update crate version in README.md
+# - Update crate version in the lib.rs documentation of feature flags
+# - Update dependency in sibling crates
+# - Remove path dependencies
+# - Update CHANGELOG.md
+# - Update if necessary copyright notice in LICENSE-MIT
+# - Create a "vX.Y.Z" git tag
+authors = ["Serge Barral <serge.barral@asynchronics.com>"]
+version = "0.3.1"
+edition = "2021"
+rust-version = "1.77.0"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/asynchronics/nexosim"
+readme = "../README.md"
+description = """
+A high performance asychronous compute framework for system simulation.
+"""
+categories = ["simulation", "aerospace", "science"]
+keywords = [
+    "simulation",
+    "discrete-event",
+    "systems",
+    "cyberphysical",
+    "real-time",
+]
+
+[features]
+server = [
+    "dep:bytes",
+    "dep:ciborium",
+    "dep:prost",
+    "dep:prost-types",
+    "dep:serde",
+    "dep:tonic",
+    "dep:tokio",
+    "dep:tokio-stream",
+    "dep:tonic",
+    "tai-time/serde",
+]
+tracing = ["dep:tracing", "dep:tracing-subscriber"]
+
+# DEVELOPMENT ONLY: API-unstable public exports meant for external test/benchmarking.
+dev-hooks = []
+
+[dependencies]
+# Mandatory dependencies.
+async-event = "0.2.1"
+crossbeam-utils = "0.8"
+diatomic-waker = "0.2.3"
+dyn-clone = "1.0"
+futures-channel = "0.3"
+futures-task = "0.3"
+multishot = "0.3.2"
+num_cpus = "1.13"
+parking = "2"
+pin-project = "1"
+recycle-box = "0.2"
+slab = "0.4"
+spin_sleep = "1"
+st3 = "0.4"
+tai-time = "0.3.3"
+
+# Optional dependencies.
+bytes = { version = "1", default-features = false, optional = true }
+ciborium = { version = "0.2.2", optional = true }
+prost = { version = "0.13", optional = true }
+prost-types = { version = "0.13", optional = true }
+serde = { version = "1", optional = true }
+tokio = { version = "1.0", features = [
+    "net",
+    "rt-multi-thread",
+], optional = true }
+tonic = { version = "0.12", default-features = false, features = [
+    "codegen",
+    "prost",
+    "server",
+], optional = true }
+tracing = { version = "0.1.40", default-features = false, features = [
+    "std",
+], optional = true }
+tracing-subscriber = { version = "0.3.18", optional = true }
+
+[target.'cfg(unix)'.dependencies]
+tokio-stream = { version = "0.1.10", features = ["net"], optional = true }
+
+[dev-dependencies]
+futures-util = "0.3"
+futures-executor = "0.3"
+tracing-subscriber = { version = "0.3.18", features = ["env-filter"] }
+
+[target.'cfg(nexosim_loom)'.dev-dependencies]
+loom = "0.7"
+waker-fn = "1.1"
+
+[target.'cfg(nexosim_server_codegen)'.build-dependencies]
+tonic-build = { version = "0.12" }
+
+[lints.rust]
+# `nexosim_loom` flag: run loom-based tests.
+# `nexosim_server_codegen` flag: regenerate gRPC code from .proto definitions.
+unexpected_cfgs = { level = "warn", check-cfg = [
+    'cfg(nexosim_loom)',
+    'cfg(nexosim_server_codegen)',
+] }
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]

nexosim/build.rs

@@ -0,0 +1,9 @@
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    #[cfg(nexosim_server_codegen)]
+    tonic_build::configure()
+        .build_client(false)
+        .out_dir("src/server/codegen/")
+        .compile_protos(&["simulation.proto"], &["src/server/api/"])?;
+
+    Ok(())
+}

nexosim/examples/assembly.rs

@@ -0,0 +1,186 @@
+//! Example: an assembly consisting of a current-controlled stepper motor and
+//! its driver.
+//!
+//! This example demonstrates in particular:
+//!
+//! * model prototypes,
+//! * submodels,
+//! * self-scheduling methods,
+//! * model initialization,
+//! * simulation monitoring with buffered event sinks.
+//!
+//! ```text
+//!                       ┌────────────────────────────────────────────┐
+//!                       │ Assembly                                   │
+//!                       │   ┌──────────┐                             │
+//!                PPS    │   │          │ coil currents  ┌─────────┐  │
+//! Pulse rate ●──────────┼──►│  Driver  ├───────────────►│         │  │
+//!              (±freq)  │   │          │    (IA, IB)    │         │  │ position
+//!                       │   └──────────┘                │  Motor  ├──┼──────────►
+//!              torque   │                               │         │  │ (0:199)
+//!       Load ●──────────┼──────────────────────────────►│         │  │
+//!                       │                               └─────────┘  │
+//!                       └────────────────────────────────────────────┘
+//! ```
+
+use std::time::Duration;
+
+use nexosim::model::{BuildContext, Model, ProtoModel};
+use nexosim::ports::{EventBuffer, Output};
+use nexosim::simulation::{Mailbox, SimInit, SimulationError};
+use nexosim::time::MonotonicTime;
+
+mod stepper_motor;
+
+pub use stepper_motor::{Driver, Motor};
+
+/// A prototype for `MotorAssembly`.
+pub struct ProtoMotorAssembly {
+    pub position: Output<u16>,
+    init_pos: u16,
+}
+
+impl ProtoMotorAssembly {
+    /// The prototype has a public constructor.
+    pub fn new(init_pos: u16) -> Self {
+        Self {
+            position: Default::default(),
+            init_pos,
+        }
+    }
+
+    // Input methods are in the model itself.
+}
+
+/// The parent model which submodels are the driver and the motor.
+pub struct MotorAssembly {
+    /// Private output for submodel connection.
+    pps: Output<f64>,
+    /// Private output for submodel connection.
+    load: Output<f64>,
+}
+
+impl MotorAssembly {
+    /// The model now has a module-private constructor.
+    fn new() -> Self {
+        Self {
+            pps: Default::default(),
+            load: Default::default(),
+        }
+    }
+
+    /// Pulse rate (sign = direction) [Hz] -- input port.
+    pub async fn pulse_rate(&mut self, pps: f64) {
+        self.pps.send(pps).await
+    }
+
+    /// Torque applied by the load [N·m] -- input port.
+    pub async fn load(&mut self, torque: f64) {
+        self.load.send(torque).await
+    }
+}
+
+impl Model for MotorAssembly {}
+
+impl ProtoModel for ProtoMotorAssembly {
+    type Model = MotorAssembly;
+
+    fn build(self, cx: &mut BuildContext<Self>) -> MotorAssembly {
+        let mut assembly = MotorAssembly::new();
+        let mut motor = Motor::new(self.init_pos);
+        let mut driver = Driver::new(1.0);
+
+        // Mailboxes.
+        let motor_mbox = Mailbox::new();
+        let driver_mbox = Mailbox::new();
+
+        // Connections.
+        assembly.pps.connect(Driver::pulse_rate, &driver_mbox);
+        assembly.load.connect(Motor::load, &motor_mbox);
+        driver.current_out.connect(Motor::current_in, &motor_mbox);
+
+        // Move the prototype's output to the submodel. The `self.position`
+        // output can be cloned if necessary if several submodels need access to
+        // it.
+        motor.position = self.position;
+
+        // Add the submodels to the simulation.
+        cx.add_submodel(driver, driver_mbox, "driver");
+        cx.add_submodel(motor, motor_mbox, "motor");
+
+        assembly
+    }
+}
+
+fn main() -> Result<(), SimulationError> {
+    // ---------------
+    // Bench assembly.
+    // ---------------
+
+    // Models.
+    let init_pos = 123;
+    let mut assembly = ProtoMotorAssembly::new(init_pos);
+
+    // Mailboxes.
+    let assembly_mbox = Mailbox::new();
+    let assembly_addr = assembly_mbox.address();
+
+    // Model handles for simulation.
+    let mut position = EventBuffer::new();
+    assembly.position.connect_sink(&position);
+
+    // Start time (arbitrary since models do not depend on absolute time).
+    let t0 = MonotonicTime::EPOCH;
+
+    // Assembly and initialization.
+    let (mut simu, scheduler) = SimInit::new()
+        .add_model(assembly, assembly_mbox, "assembly")
+        .init(t0)?;
+
+    // ----------
+    // Simulation.
+    // ----------
+
+    // Check initial conditions.
+    let mut t = t0;
+    assert_eq!(simu.time(), t);
+    assert_eq!(position.next(), Some(init_pos));
+    assert!(position.next().is_none());
+
+    // Start the motor in 2s with a PPS of 10Hz.
+    scheduler
+        .schedule_event(
+            Duration::from_secs(2),
+            MotorAssembly::pulse_rate,
+            10.0,
+            &assembly_addr,
+        )
+        .unwrap();
+
+    // Advance simulation time to two next events.
+    simu.step()?;
+    t += Duration::new(2, 0);
+    assert_eq!(simu.time(), t);
+    simu.step()?;
+    t += Duration::new(0, 100_000_000);
+    assert_eq!(simu.time(), t);
+
+    // Whichever the starting position, after two phase increments from the
+    // driver the rotor should have synchronized with the driver, with a
+    // position given by this beautiful formula.
+    let mut pos = (((init_pos + 1) / 4) * 4 + 1) % Motor::STEPS_PER_REV;
+    assert_eq!(position.by_ref().last().unwrap(), pos);
+
+    // Advance simulation time by 0.9s, which with a 10Hz PPS should correspond to
+    // 9 position increments.
+    simu.step_until(Duration::new(0, 900_000_000))?;
+    t += Duration::new(0, 900_000_000);
+    assert_eq!(simu.time(), t);
+    for _ in 0..9 {
+        pos = (pos + 1) % Motor::STEPS_PER_REV;
+        assert_eq!(position.next(), Some(pos));
+    }
+    assert!(position.next().is_none());
+
+    Ok(())
+}

nexosim/examples/espresso_machine.rs

@@ -12,9 +12,9 @@
 //!                                ┌─────────────────────────────────────────────┐
 //!                                │                     (≥0)                    │
 //!                                │    ┌────────────┐                           │
-//!                                └───▶│            │                           │
+//!                                └───►│            │                           │
 //!                   added volume      │ Water tank ├────┐                      │
-//!     Water fill ●───────────────────▶│            │    │                      │
+//!     Water fill ●───────────────────►│            │    │                      │
 //!                      (>0)           └────────────┘    │                      │
 //!                                                       │                      │
 //!                                      water sense      │                      │
@@ -22,22 +22,21 @@
 //!                                │  (empty|not empty)                          │
 //!                                │                                             │
 //!                                │    ┌────────────┐          ┌────────────┐   │
-//!                    brew time   └───▶│            │ command  │            │   │
-//! Brew time dial ●───────────────────▶│ Controller ├─────────▶│ Water pump ├───┘
-//!                      (>0)      ┌───▶│            │ (on|off) │            │
+//!                    brew time   └───►│            │ command  │            │   │
+//! Brew time dial ●───────────────────►│ Controller ├─────────►│ Water pump ├───┘
+//!                      (>0)      ┌───►│            │ (on|off) │            │
 //!                                │    └────────────┘          └────────────┘
 //!                    trigger     │
 //!   Brew command ●───────────────┘
 //!                      (-)
 //! ```
 
-use std::future::Future;
-use std::pin::Pin;
 use std::time::Duration;
 
-use asynchronix::model::{InitializedModel, Model, Output};
-use asynchronix::simulation::{Mailbox, SimInit};
-use asynchronix::time::{EventKey, MonotonicTime, Scheduler};
+use nexosim::model::{Context, InitializedModel, Model};
+use nexosim::ports::{EventSlot, Output};
+use nexosim::simulation::{ActionKey, Mailbox, SimInit, SimulationError};
+use nexosim::time::MonotonicTime;
 
 /// Water pump.
 pub struct Pump {
@@ -81,7 +80,7 @@ pub struct Controller {
     water_sense: WaterSenseState,
     /// Event key, which if present indicates that the machine is currently
     /// brewing -- internal state.
-    stop_brew_key: Option<EventKey>,
+    stop_brew_key: Option<ActionKey>,
 }
 
 impl Controller {
@@ -121,7 +120,7 @@ impl Controller {
     }
 
     /// Starts brewing or cancels the current brew -- input port.
-    pub async fn brew_cmd(&mut self, _: (), scheduler: &Scheduler<Self>) {
+    pub async fn brew_cmd(&mut self, _: (), cx: &mut Context<Self>) {
         // If a brew was ongoing, sending the brew command is interpreted as a
         // request to cancel it.
         if let Some(key) = self.stop_brew_key.take() {
@@ -140,8 +139,7 @@ impl Controller {
 
         // Schedule the `stop_brew()` method and turn on the pump.
         self.stop_brew_key = Some(
-            scheduler
-                .schedule_keyed_event(self.brew_time, Self::stop_brew, ())
+            cx.schedule_keyed_event(self.brew_time, Self::stop_brew, ())
                 .unwrap(),
         );
         self.pump_cmd.send(PumpCommand::On).await;
@@ -189,7 +187,7 @@ impl Tank {
     }
 
     /// Water volume added [m³] -- input port.
-    pub async fn fill(&mut self, added_volume: f64, scheduler: &Scheduler<Self>) {
+    pub async fn fill(&mut self, added_volume: f64, cx: &mut Context<Self>) {
         // Ignore zero and negative values. We could also impose a maximum based
         // on tank capacity.
         if added_volume <= 0.0 {
@@ -207,11 +205,11 @@ impl Tank {
             state.set_empty_key.cancel();
 
             // Update the volume, saturating at 0 in case of rounding errors.
-            let time = scheduler.time();
+            let time = cx.time();
             let elapsed_time = time.duration_since(state.last_volume_update).as_secs_f64();
             self.volume = (self.volume - state.flow_rate * elapsed_time).max(0.0);
 
-            self.schedule_empty(state.flow_rate, time, scheduler).await;
+            self.schedule_empty(state.flow_rate, time, cx).await;
 
             // There is no need to broadcast the state of the water sense since
             // it could not be previously `Empty` (otherwise the dynamic state
@@ -229,10 +227,10 @@ impl Tank {
     /// # Panics
     ///
     /// This method will panic if the flow rate is negative.
-    pub async fn set_flow_rate(&mut self, flow_rate: f64, scheduler: &Scheduler<Self>) {
+    pub async fn set_flow_rate(&mut self, flow_rate: f64, cx: &mut Context<Self>) {
         assert!(flow_rate >= 0.0);
 
-        let time = scheduler.time();
+        let time = cx.time();
 
         // If the flow rate was non-zero up to now, update the volume.
         if let Some(state) = self.dynamic_state.take() {
@@ -244,7 +242,7 @@ impl Tank {
             self.volume = (self.volume - state.flow_rate * elapsed_time).max(0.0);
         }
 
-        self.schedule_empty(flow_rate, time, scheduler).await;
+        self.schedule_empty(flow_rate, time, cx).await;
     }
 
     /// Schedules a callback for when the tank becomes empty.
@@ -257,7 +255,7 @@ impl Tank {
         &mut self,
         flow_rate: f64,
         time: MonotonicTime,
-        scheduler: &Scheduler<Self>,
+        cx: &mut Context<Self>,
     ) {
         // Determine when the tank will be empty at the current flow rate.
         let duration_until_empty = if self.volume == 0.0 {
@@ -274,7 +272,7 @@ impl Tank {
         let duration_until_empty = Duration::from_secs_f64(duration_until_empty);
 
         // Schedule the next update.
-        match scheduler.schedule_keyed_event(duration_until_empty, Self::set_empty, ()) {
+        match cx.schedule_keyed_event(duration_until_empty, Self::set_empty, ()) {
             Ok(set_empty_key) => {
                 let state = TankDynamicState {
                     last_volume_update: time,
@@ -301,21 +299,16 @@ impl Tank {
 
 impl Model for Tank {
     /// Broadcasts the initial state of the water sense.
-    fn init(
-        mut self,
-        _scheduler: &Scheduler<Self>,
-    ) -> Pin<Box<dyn Future<Output = InitializedModel<Self>> + Send + '_>> {
-        Box::pin(async move {
-            self.water_sense
-                .send(if self.volume == 0.0 {
-                    WaterSenseState::Empty
-                } else {
-                    WaterSenseState::NotEmpty
-                })
-                .await;
+    async fn init(mut self, _: &mut Context<Self>) -> InitializedModel<Self> {
+        self.water_sense
+            .send(if self.volume == 0.0 {
+                WaterSenseState::Empty
+            } else {
+                WaterSenseState::NotEmpty
+            })
+            .await;
 
-            self.into()
-        })
+        self.into()
     }
 }
 
@@ -323,7 +316,7 @@ impl Model for Tank {
 /// is non-zero.
 struct TankDynamicState {
     last_volume_update: MonotonicTime,
-    set_empty_key: EventKey,
+    set_empty_key: ActionKey,
     flow_rate: f64,
 }
 
@@ -334,7 +327,7 @@ pub enum WaterSenseState {
     NotEmpty,
 }
 
-fn main() {
+fn main() -> Result<(), SimulationError> {
     // ---------------
     // Bench assembly.
     // ---------------
@@ -364,7 +357,8 @@ fn main() {
     pump.flow_rate.connect(Tank::set_flow_rate, &tank_mbox);
 
     // Model handles for simulation.
-    let mut flow_rate = pump.flow_rate.connect_slot().0;
+    let mut flow_rate = EventSlot::new();
+    pump.flow_rate.connect_sink(&flow_rate);
     let controller_addr = controller_mbox.address();
     let tank_addr = tank_mbox.address();
 
@@ -372,11 +366,11 @@ fn main() {
     let t0 = MonotonicTime::EPOCH;
 
     // Assembly and initialization.
-    let mut simu = SimInit::new()
-        .add_model(controller, controller_mbox)
-        .add_model(pump, pump_mbox)
-        .add_model(tank, tank_mbox)
-        .init(t0);
+    let (mut simu, scheduler) = SimInit::new()
+        .add_model(controller, controller_mbox, "controller")
+        .add_model(pump, pump_mbox, "pump")
+        .add_model(tank, tank_mbox, "tank")
+        .init(t0)?;
 
     // ----------
     // Simulation.
@@ -387,62 +381,65 @@ fn main() {
     assert_eq!(simu.time(), t);
 
     // Brew one espresso shot with the default brew time.
-    simu.send_event(Controller::brew_cmd, (), &controller_addr);
-    assert_eq!(flow_rate.take(), Some(pump_flow_rate));
+    simu.process_event(Controller::brew_cmd, (), &controller_addr)?;
+    assert_eq!(flow_rate.next(), Some(pump_flow_rate));
 
-    simu.step();
+    simu.step()?;
     t += Controller::DEFAULT_BREW_TIME;
     assert_eq!(simu.time(), t);
-    assert_eq!(flow_rate.take(), Some(0.0));
+    assert_eq!(flow_rate.next(), Some(0.0));
 
     // Drink too much coffee.
     let volume_per_shot = pump_flow_rate * Controller::DEFAULT_BREW_TIME.as_secs_f64();
     let shots_per_tank = (init_tank_volume / volume_per_shot) as u64; // YOLO--who cares about floating-point rounding errors?
     for _ in 0..(shots_per_tank - 1) {
-        simu.send_event(Controller::brew_cmd, (), &controller_addr);
-        assert_eq!(flow_rate.take(), Some(pump_flow_rate));
-        simu.step();
+        simu.process_event(Controller::brew_cmd, (), &controller_addr)?;
+        assert_eq!(flow_rate.next(), Some(pump_flow_rate));
+        simu.step()?;
         t += Controller::DEFAULT_BREW_TIME;
         assert_eq!(simu.time(), t);
-        assert_eq!(flow_rate.take(), Some(0.0));
+        assert_eq!(flow_rate.next(), Some(0.0));
     }
 
     // Check that the tank becomes empty before the completion of the next shot.
-    simu.send_event(Controller::brew_cmd, (), &controller_addr);
-    simu.step();
+    simu.process_event(Controller::brew_cmd, (), &controller_addr)?;
+    simu.step()?;
     assert!(simu.time() < t + Controller::DEFAULT_BREW_TIME);
     t = simu.time();
-    assert_eq!(flow_rate.take(), Some(0.0));
+    assert_eq!(flow_rate.next(), Some(0.0));
 
     // Try to brew another shot while the tank is still empty.
-    simu.send_event(Controller::brew_cmd, (), &controller_addr);
-    assert!(flow_rate.take().is_none());
+    simu.process_event(Controller::brew_cmd, (), &controller_addr)?;
+    assert!(flow_rate.next().is_none());
 
     // Change the brew time and fill up the tank.
     let brew_time = Duration::new(30, 0);
-    simu.send_event(Controller::brew_time, brew_time, &controller_addr);
-    simu.send_event(Tank::fill, 1.0e-3, tank_addr);
-    simu.send_event(Controller::brew_cmd, (), &controller_addr);
-    assert_eq!(flow_rate.take(), Some(pump_flow_rate));
+    simu.process_event(Controller::brew_time, brew_time, &controller_addr)?;
+    simu.process_event(Tank::fill, 1.0e-3, tank_addr)?;
+    simu.process_event(Controller::brew_cmd, (), &controller_addr)?;
+    assert_eq!(flow_rate.next(), Some(pump_flow_rate));
 
-    simu.step();
+    simu.step()?;
     t += brew_time;
     assert_eq!(simu.time(), t);
-    assert_eq!(flow_rate.take(), Some(0.0));
+    assert_eq!(flow_rate.next(), Some(0.0));
 
     // Interrupt the brew after 15s by pressing again the brew button.
-    simu.schedule_event(
-        Duration::from_secs(15),
-        Controller::brew_cmd,
-        (),
-        &controller_addr,
-    )
-    .unwrap();
-    simu.send_event(Controller::brew_cmd, (), &controller_addr);
-    assert_eq!(flow_rate.take(), Some(pump_flow_rate));
+    scheduler
+        .schedule_event(
+            Duration::from_secs(15),
+            Controller::brew_cmd,
+            (),
+            &controller_addr,
+        )
+        .unwrap();
+    simu.process_event(Controller::brew_cmd, (), &controller_addr)?;
+    assert_eq!(flow_rate.next(), Some(pump_flow_rate));
 
-    simu.step();
+    simu.step()?;
     t += Duration::from_secs(15);
     assert_eq!(simu.time(), t);
-    assert_eq!(flow_rate.take(), Some(0.0));
+    assert_eq!(flow_rate.next(), Some(0.0));
+
+    Ok(())
 }

nexosim/examples/external_input.rs

@@ -0,0 +1,257 @@
+//! Example: a model that reads data external to the simulation.
+//!
+//! This example demonstrates in particular:
+//!
+//! * processing of external inputs (useful in co-simulation),
+//! * system clock,
+//! * periodic scheduling.
+//!
+//! ```text
+//!                                                 ┏━━━━━━━━━━━━━━━━━━━━━━━━┓
+//!                                                 ┃ Simulation             ┃
+//! ┌╌╌╌╌╌╌╌╌╌╌╌╌┐         ┌╌╌╌╌╌╌╌╌╌╌╌╌┐           ┃   ┌──────────┐         ┃
+//! ┆            ┆ message ┆            ┆  message  ┃   │          │ message ┃
+//! ┆ UDP Client ├╌╌╌╌╌╌╌╌►┆ UDP Server ├╌╌╌╌╌╌╌╌╌╌╌╂╌╌►│ Listener ├─────────╂─►
+//! ┆            ┆  [UDP]  ┆            ┆ [channel] ┃   │          │         ┃
+//! └╌╌╌╌╌╌╌╌╌╌╌╌┘         └╌╌╌╌╌╌╌╌╌╌╌╌┘           ┃   └──────────┘         ┃
+//!                                                 ┗━━━━━━━━━━━━━━━━━━━━━━━━┛
+//! ```
+
+use std::io::ErrorKind;
+use std::net::{Ipv4Addr, UdpSocket};
+use std::sync::mpsc::{channel, Receiver, Sender};
+use std::sync::{Arc, Condvar, Mutex};
+use std::thread::{self, sleep, JoinHandle};
+use std::time::Duration;
+
+use nexosim::model::{BuildContext, Context, InitializedModel, Model, ProtoModel};
+use nexosim::ports::{EventBuffer, Output};
+use nexosim::simulation::{Mailbox, SimInit, SimulationError};
+use nexosim::time::{AutoSystemClock, MonotonicTime};
+
+const DELTA: Duration = Duration::from_millis(2);
+const PERIOD: Duration = Duration::from_millis(20);
+const N: usize = 10;
+const SHUTDOWN_SIGNAL: &str = "<SHUTDOWN>";
+const SENDER: (Ipv4Addr, u16) = (Ipv4Addr::new(127, 0, 0, 1), 8000);
+const RECEIVER: (Ipv4Addr, u16) = (Ipv4Addr::new(127, 0, 0, 1), 9000);
+
+/// Prototype for the `Listener` Model.
+pub struct ProtoListener {
+    /// Received message.
+    pub message: Output<String>,
+
+    /// Notifier to start the UDP client.
+    start: Notifier,
+}
+
+impl ProtoListener {
+    fn new(start: Notifier) -> Self {
+        Self {
+            message: Output::default(),
+            start,
+        }
+    }
+}
+
+impl ProtoModel for ProtoListener {
+    type Model = Listener;
+
+    /// Start the UDP Server immediately upon model construction.
+    fn build(self, _: &mut BuildContext<Self>) -> Listener {
+        let (tx, rx) = channel();
+
+        let external_handle = thread::spawn(move || {
+            Listener::listen(tx, self.start);
+        });
+
+        Listener::new(self.message, rx, external_handle)
+    }
+}
+
+/// Model that asynchronously receives messages external to the simulation.
+pub struct Listener {
+    /// Received message.
+    message: Output<String>,
+
+    /// Receiver of external messages.
+    rx: Receiver<String>,
+
+    /// Handle to UDP Server.
+    server_handle: Option<JoinHandle<()>>,
+}
+
+impl Listener {
+    /// Creates a Listener.
+    pub fn new(
+        message: Output<String>,
+        rx: Receiver<String>,
+        server_handle: JoinHandle<()>,
+    ) -> Self {
+        Self {
+            message,
+            rx,
+            server_handle: Some(server_handle),
+        }
+    }
+
+    /// Periodically scheduled function that processes external events.
+    async fn process(&mut self) {
+        while let Ok(message) = self.rx.try_recv() {
+            self.message.send(message).await;
+        }
+    }
+
+    /// Starts the UDP server.
+    fn listen(tx: Sender<String>, start: Notifier) {
+        let socket = UdpSocket::bind(RECEIVER).unwrap();
+        let mut buf = [0; 1 << 16];
+
+        // Wake up the client.
+        start.notify();
+
+        loop {
+            match socket.recv_from(&mut buf) {
+                Ok((packet_size, _)) => {
+                    if let Ok(message) = std::str::from_utf8(&buf[..packet_size]) {
+                        if message == SHUTDOWN_SIGNAL {
+                            break;
+                        }
+                        // Inject external message into simulation.
+                        if tx.send(message.into()).is_err() {
+                            break;
+                        }
+                    };
+                }
+                Err(e) if e.kind() == ErrorKind::Interrupted => {
+                    continue;
+                }
+                _ => {
+                    break;
+                }
+            }
+        }
+    }
+}
+
+impl Model for Listener {
+    /// Initialize model.
+    async fn init(self, cx: &mut Context<Self>) -> InitializedModel<Self> {
+        // Schedule periodic function that processes external events.
+        cx.schedule_periodic_event(DELTA, PERIOD, Listener::process, ())
+            .unwrap();
+
+        self.into()
+    }
+}
+
+impl Drop for Listener {
+    /// Wait for UDP Server shutdown.
+    fn drop(&mut self) {
+        if let Some(handle) = self.server_handle.take() {
+            let _ = handle.join();
+        };
+    }
+}
+
+/// A synchronization barrier that can be unblocked by a notifier.
+struct WaitBarrier(Arc<(Mutex<bool>, Condvar)>);
+
+impl WaitBarrier {
+    fn new() -> Self {
+        Self(Arc::new((Mutex::new(false), Condvar::new())))
+    }
+    fn notifier(&self) -> Notifier {
+        Notifier(self.0.clone())
+    }
+    fn wait(self) {
+        let _unused = self
+            .0
+             .1
+            .wait_while(self.0 .0.lock().unwrap(), |pending| *pending)
+            .unwrap();
+    }
+}
+
+/// A notifier for the associated synchronization barrier.
+struct Notifier(Arc<(Mutex<bool>, Condvar)>);
+
+impl Notifier {
+    fn notify(self) {
+        *self.0 .0.lock().unwrap() = false;
+        self.0 .1.notify_one();
+    }
+}
+
+fn main() -> Result<(), SimulationError> {
+    // ---------------
+    // Bench assembly.
+    // ---------------
+
+    // Models.
+
+    // Synchronization barrier for the UDP client.
+    let start = WaitBarrier::new();
+
+    // Prototype of the listener model.
+    let mut listener = ProtoListener::new(start.notifier());
+
+    // Mailboxes.
+    let listener_mbox = Mailbox::new();
+
+    // Model handles for simulation.
+    let mut message = EventBuffer::with_capacity(N + 1);
+    listener.message.connect_sink(&message);
+
+    // Start time (arbitrary since models do not depend on absolute time).
+    let t0 = MonotonicTime::EPOCH;
+
+    // Assembly and initialization.
+    let mut simu = SimInit::new()
+        .add_model(listener, listener_mbox, "listener")
+        .set_clock(AutoSystemClock::new())
+        .init(t0)?
+        .0;
+
+    // ----------
+    // Simulation.
+    // ----------
+
+    // External client that sends UDP messages.
+    let sender_handle = thread::spawn(move || {
+        let socket = UdpSocket::bind(SENDER).unwrap();
+
+        // Wait until the UDP Server is ready.
+        start.wait();
+
+        for i in 0..N {
+            socket.send_to(i.to_string().as_bytes(), RECEIVER).unwrap();
+            if i % 3 == 0 {
+                sleep(PERIOD * i as u32)
+            }
+        }
+
+        socket
+    });
+
+    // Advance simulation, external messages will be collected.
+    simu.step_until(Duration::from_secs(2))?;
+
+    // Shut down the server.
+    let socket = sender_handle.join().unwrap();
+    socket
+        .send_to(SHUTDOWN_SIGNAL.as_bytes(), RECEIVER)
+        .unwrap();
+
+    // Check collected external messages.
+    let mut packets = 0_u32;
+    for _ in 0..N {
+        // Check all messages accounting for possible UDP packet re-ordering,
+        // but assuming no packet loss.
+        packets |= 1 << message.next().unwrap().parse::<u8>().unwrap();
+    }
+    assert_eq!(packets, u32::MAX >> 22);
+    assert_eq!(message.next(), None);
+
+    Ok(())
+}

nexosim/examples/infinite_loop.rs

@@ -0,0 +1,131 @@
+//! Example: a simulation that runs infinitely, receiving data from
+//! outside. This setup is typical for hardware-in-the-loop use case.
+//!
+//! This example demonstrates in particular:
+//!
+//! * infinite simulation (useful in hardware-in-the-loop),
+//! * simulation halting,
+//! * processing of external data (useful in co-simulation),
+//! * system clock,
+//! * periodic scheduling.
+//!
+//! ```text
+//!                              ┏━━━━━━━━━━━━━━━━━━━━━━━━┓
+//!                              ┃ Simulation             ┃
+//!┌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┐           ┃   ┌──────────┐         ┃
+//!┆                 ┆  message  ┃   │          │ message ┃
+//!┆ External thread ├╌╌╌╌╌╌╌╌╌╌╌╂╌╌►│ Listener ├─────────╂─►
+//!┆                 ┆ [channel] ┃   │          │         ┃
+//!└╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┘           ┃   └──────────┘         ┃
+//!                              ┗━━━━━━━━━━━━━━━━━━━━━━━━┛
+//! ```
+
+use std::sync::mpsc::{channel, Receiver};
+use std::thread::{self, sleep};
+use std::time::Duration;
+
+use nexosim::model::{Context, InitializedModel, Model};
+use nexosim::ports::{EventBuffer, Output};
+use nexosim::simulation::{ExecutionError, Mailbox, SimInit, SimulationError};
+use nexosim::time::{AutoSystemClock, MonotonicTime};
+
+const DELTA: Duration = Duration::from_millis(2);
+const PERIOD: Duration = Duration::from_millis(20);
+const N: usize = 10;
+
+/// The `Listener` Model.
+pub struct Listener {
+    /// Received message.
+    pub message: Output<String>,
+
+    /// Source of external messages.
+    external: Receiver<String>,
+}
+
+impl Listener {
+    /// Creates new `Listener` model.
+    fn new(external: Receiver<String>) -> Self {
+        Self {
+            message: Output::default(),
+            external,
+        }
+    }
+
+    /// Periodically scheduled function that processes external events.
+    async fn process(&mut self) {
+        while let Ok(message) = self.external.try_recv() {
+            self.message.send(message).await;
+        }
+    }
+}
+
+impl Model for Listener {
+    /// Initialize model.
+    async fn init(self, cx: &mut Context<Self>) -> InitializedModel<Self> {
+        // Schedule periodic function that processes external events.
+        cx.schedule_periodic_event(DELTA, PERIOD, Listener::process, ())
+            .unwrap();
+
+        self.into()
+    }
+}
+
+fn main() -> Result<(), SimulationError> {
+    // ---------------
+    // Bench assembly.
+    // ---------------
+
+    // Channel for communication with simulation from outside.
+    let (tx, rx) = channel();
+
+    // Models.
+
+    // The listener model.
+    let mut listener = Listener::new(rx);
+
+    // Mailboxes.
+    let listener_mbox = Mailbox::new();
+
+    // Model handles for simulation.
+    let mut message = EventBuffer::with_capacity(N + 1);
+    listener.message.connect_sink(&message);
+
+    // Start time (arbitrary since models do not depend on absolute time).
+    let t0 = MonotonicTime::EPOCH;
+
+    // Assembly and initialization.
+    let (mut simu, mut scheduler) = SimInit::new()
+        .add_model(listener, listener_mbox, "listener")
+        .set_clock(AutoSystemClock::new())
+        .init(t0)?;
+
+    // Simulation thread.
+    let simulation_handle = thread::spawn(move || {
+        // ----------
+        // Simulation.
+        // ----------
+        simu.step_unbounded()
+    });
+
+    // Send data to simulation from outside.
+    for i in 0..N {
+        tx.send(i.to_string()).unwrap();
+        if i % 3 == 0 {
+            sleep(PERIOD * i as u32)
+        }
+    }
+
+    // Check collected external messages.
+    for i in 0..N {
+        assert_eq!(message.next().unwrap(), i.to_string());
+    }
+    assert_eq!(message.next(), None);
+
+    // Stop the simulation.
+    scheduler.halt();
+    match simulation_handle.join().unwrap() {
+        Err(ExecutionError::Halted) => Ok(()),
+        Err(e) => Err(e.into()),
+        _ => Ok(()),
+    }
+}

nexosim/examples/power_supply.rs

@@ -8,27 +8,28 @@
 //! ```text
 //!                                                     ┌────────┐
 //!                                                     │        │
-//!                                                ┌───▶│  Load  ├───▶ Power
+//!                                                ┌──◄►│  Load  ├───► Power
 //!                                                │    │        │
 //!                                                │    └────────┘
 //!                                                │
 //!                                                │    ┌────────┐
 //!                                                │    │        │
-//!                                                ├───▶│  Load  ├───▶ Power
+//!                                                ├──◄►│  Load  ├───► Power
 //!                                                │    │        │
 //!                                                │    └────────┘
 //!                                                │
 //!                                                │    ┌────────┐
-//!                       ┌──────────┐   voltage▶  │    │        │
-//! Voltage setting ●────▶│          │◀────────────┴───▶│  Load  ├───▶ Power
-//!                       │  Power   │  ◀current        │        │
+//!                       ┌──────────┐   voltage►  │    │        │
+//! Voltage setting ●────►│          │►◄───────────┴──◄►│  Load  ├───► Power
+//!                       │  Power   │  ◄current        │        │
 //!                       │  supply  │                  └────────┘
-//!                       │          ├───────────────────────────────▶ Total power
+//!                       │          ├───────────────────────────────► Total power
 //!                       └──────────┘
 //! ```
-use asynchronix::model::{Model, Output, Requestor};
-use asynchronix::simulation::{Mailbox, SimInit};
-use asynchronix::time::MonotonicTime;
+use nexosim::model::Model;
+use nexosim::ports::{EventSlot, Output, Requestor};
+use nexosim::simulation::{Mailbox, SimInit, SimulationError};
+use nexosim::time::MonotonicTime;
 
 /// Power supply.
 pub struct PowerSupply {
@@ -98,7 +99,7 @@ impl Load {
 
 impl Model for Load {}
 
-fn main() {
+fn main() -> Result<(), SimulationError> {
     // ---------------
     // Bench assembly.
     // ---------------
@@ -124,10 +125,14 @@ fn main() {
     psu.pwr_out.connect(Load::pwr_in, &load3_mbox);
 
     // Model handles for simulation.
-    let mut psu_power = psu.power.connect_slot().0;
-    let mut load1_power = load1.power.connect_slot().0;
-    let mut load2_power = load2.power.connect_slot().0;
-    let mut load3_power = load3.power.connect_slot().0;
+    let mut psu_power = EventSlot::new();
+    let mut load1_power = EventSlot::new();
+    let mut load2_power = EventSlot::new();
+    let mut load3_power = EventSlot::new();
+    psu.power.connect_sink(&psu_power);
+    load1.power.connect_sink(&load1_power);
+    load2.power.connect_sink(&load2_power);
+    load3.power.connect_sink(&load3_power);
     let psu_addr = psu_mbox.address();
 
     // Start time (arbitrary since models do not depend on absolute time).
@@ -135,11 +140,12 @@ fn main() {
 
     // Assembly and initialization.
     let mut simu = SimInit::new()
-        .add_model(psu, psu_mbox)
-        .add_model(load1, load1_mbox)
-        .add_model(load2, load2_mbox)
-        .add_model(load3, load3_mbox)
-        .init(t0);
+        .add_model(psu, psu_mbox, "psu")
+        .add_model(load1, load1_mbox, "load1")
+        .add_model(load2, load2_mbox, "load2")
+        .add_model(load3, load3_mbox, "load3")
+        .init(t0)?
+        .0;
 
     // ----------
     // Simulation.
@@ -153,15 +159,17 @@ fn main() {
 
     // Vary the supply voltage, check the load and power supply consumptions.
     for voltage in [10.0, 15.0, 20.0] {
-        simu.send_event(PowerSupply::voltage_setting, voltage, &psu_addr);
+        simu.process_event(PowerSupply::voltage_setting, voltage, &psu_addr)?;
 
         let v_square = voltage * voltage;
-        assert!(same_power(load1_power.take().unwrap(), v_square / r1));
-        assert!(same_power(load2_power.take().unwrap(), v_square / r2));
-        assert!(same_power(load3_power.take().unwrap(), v_square / r3));
+        assert!(same_power(load1_power.next().unwrap(), v_square / r1));
+        assert!(same_power(load2_power.next().unwrap(), v_square / r2));
+        assert!(same_power(load3_power.next().unwrap(), v_square / r3));
         assert!(same_power(
-            psu_power.take().unwrap(),
+            psu_power.next().unwrap(),
             v_square * (1.0 / r1 + 1.0 / r2 + 1.0 / r3)
         ));
     }
+
+    Ok(())
 }

nexosim/examples/stepper_motor.rs

@@ -4,23 +4,26 @@
 //!
 //! * self-scheduling methods,
 //! * model initialization,
-//! * simulation monitoring with event streams.
+//! * simulation monitoring with buffered event sinks.
 //!
 //! ```text
-//!                       ┌──────────┐                ┌──────────┐
-//!                PPS    │          │ coil currents  │          │ position
-//! Pulse rate ●─────────▶│  Driver  ├───────────────▶│  Motor   ├──────────▶
-//!              (±freq)  │          │    (IA, IB)    │          │ (0:199)
-//!                       └──────────┘                └──────────┘
+//!                       ┌──────────┐
+//!                PPS    │          │ coil currents  ┌─────────┐
+//! Pulse rate ●─────────►│  Driver  ├───────────────►│         │
+//!              (±freq)  │          │    (IA, IB)    │         │ position
+//!                       └──────────┘                │  Motor  ├──────────►
+//!                                       torque      │         │ (0:199)
+//!       Load ●─────────────────────────────────────►│         │
+//!                                                   └─────────┘
 //! ```
 
 use std::future::Future;
-use std::pin::Pin;
 use std::time::Duration;
 
-use asynchronix::model::{InitializedModel, Model, Output};
-use asynchronix::simulation::{Mailbox, SimInit};
-use asynchronix::time::{MonotonicTime, Scheduler};
+use nexosim::model::{Context, InitializedModel, Model};
+use nexosim::ports::{EventBuffer, Output};
+use nexosim::simulation::{Mailbox, SimInit};
+use nexosim::time::MonotonicTime;
 
 /// Stepper motor.
 pub struct Motor {
@@ -40,7 +43,7 @@ impl Motor {
     pub const TORQUE_CONSTANT: f64 = 1.0;
 
     /// Creates a motor with the specified initial position.
-    fn new(position: u16) -> Self {
+    pub fn new(position: u16) -> Self {
         Self {
             position: Default::default(),
             pos: position % Self::STEPS_PER_REV,
@@ -87,15 +90,9 @@ impl Motor {
 
 impl Model for Motor {
     /// Broadcasts the initial position of the motor.
-    fn init(
-        mut self,
-        _scheduler: &Scheduler<Self>,
-    ) -> Pin<Box<dyn Future<Output = InitializedModel<Self>> + Send + '_>> {
-        Box::pin(async move {
-            self.position.send(self.pos).await;
-
-            self.into()
-        })
+    async fn init(mut self, _: &mut Context<Self>) -> InitializedModel<Self> {
+        self.position.send(self.pos).await;
+        self.into()
     }
 }
 
@@ -128,8 +125,8 @@ impl Driver {
         }
     }
 
-    /// Sets the pulse rate (sign = direction) [Hz] -- input port.
-    pub async fn pulse_rate(&mut self, pps: f64, scheduler: &Scheduler<Self>) {
+    /// Pulse rate (sign = direction) [Hz] -- input port.
+    pub async fn pulse_rate(&mut self, pps: f64, cx: &mut Context<Self>) {
         let pps = pps.signum() * pps.abs().clamp(Self::MIN_PPS, Self::MAX_PPS);
         if pps == self.pps {
             return;
@@ -141,7 +138,7 @@ impl Driver {
         // Trigger the rotation if the motor is currently idle. Otherwise the
         // new value will be accounted for at the next pulse.
         if is_idle {
-            self.send_pulse((), scheduler).await;
+            self.send_pulse((), cx).await;
         }
     }
 
@@ -152,7 +149,7 @@ impl Driver {
     fn send_pulse<'a>(
         &'a mut self,
         _: (),
-        scheduler: &'a Scheduler<Self>,
+        cx: &'a mut Context<Self>,
     ) -> impl Future<Output = ()> + Send + 'a {
         async move {
             let current_out = match self.next_phase {
@@ -173,8 +170,7 @@ impl Driver {
             let pulse_duration = Duration::from_secs_f64(1.0 / self.pps.abs());
 
             // Schedule the next pulse.
-            scheduler
-                .schedule_event(pulse_duration, Self::send_pulse, ())
+            cx.schedule_event(pulse_duration, Self::send_pulse, ())
                 .unwrap();
         }
     }
@@ -182,7 +178,8 @@ impl Driver {
 
 impl Model for Driver {}
 
-fn main() {
+#[allow(dead_code)]
+fn main() -> Result<(), nexosim::simulation::SimulationError> {
     // ---------------
     // Bench assembly.
     // ---------------
@@ -200,7 +197,8 @@ fn main() {
     driver.current_out.connect(Motor::current_in, &motor_mbox);
 
     // Model handles for simulation.
-    let mut position = motor.position.connect_stream().0;
+    let mut position = EventBuffer::new();
+    motor.position.connect_sink(&position);
     let motor_addr = motor_mbox.address();
     let driver_addr = driver_mbox.address();
 
@@ -208,10 +206,10 @@ fn main() {
     let t0 = MonotonicTime::EPOCH;
 
     // Assembly and initialization.
-    let mut simu = SimInit::new()
-        .add_model(driver, driver_mbox)
-        .add_model(motor, motor_mbox)
-        .init(t0);
+    let (mut simu, scheduler) = SimInit::new()
+        .add_model(driver, driver_mbox, "driver")
+        .add_model(motor, motor_mbox, "motor")
+        .init(t0)?;
 
     // ----------
     // Simulation.
@@ -224,19 +222,20 @@ fn main() {
     assert!(position.next().is_none());
 
     // Start the motor in 2s with a PPS of 10Hz.
-    simu.schedule_event(
-        Duration::from_secs(2),
-        Driver::pulse_rate,
-        10.0,
-        &driver_addr,
-    )
-    .unwrap();
+    scheduler
+        .schedule_event(
+            Duration::from_secs(2),
+            Driver::pulse_rate,
+            10.0,
+            &driver_addr,
+        )
+        .unwrap();
 
     // Advance simulation time to two next events.
-    simu.step();
+    simu.step()?;
     t += Duration::new(2, 0);
     assert_eq!(simu.time(), t);
-    simu.step();
+    simu.step()?;
     t += Duration::new(0, 100_000_000);
     assert_eq!(simu.time(), t);
 
@@ -248,7 +247,7 @@ fn main() {
 
     // Advance simulation time by 0.9s, which with a 10Hz PPS should correspond to
     // 9 position increments.
-    simu.step_by(Duration::new(0, 900_000_000));
+    simu.step_until(Duration::new(0, 900_000_000))?;
     t += Duration::new(0, 900_000_000);
     assert_eq!(simu.time(), t);
     for _ in 0..9 {
@@ -258,24 +257,24 @@ fn main() {
     assert!(position.next().is_none());
 
     // Increase the load beyond the torque limit for a 1A driver current.
-    simu.send_event(Motor::load, 2.0, &motor_addr);
+    simu.process_event(Motor::load, 2.0, &motor_addr)?;
 
     // Advance simulation time and check that the motor is blocked.
-    simu.step();
+    simu.step()?;
     t += Duration::new(0, 100_000_000);
     assert_eq!(simu.time(), t);
     assert!(position.next().is_none());
 
     // Do it again.
-    simu.step();
+    simu.step()?;
     t += Duration::new(0, 100_000_000);
     assert_eq!(simu.time(), t);
     assert!(position.next().is_none());
 
     // Decrease the load below the torque limit for a 1A driver current and
     // advance simulation time.
-    simu.send_event(Motor::load, 0.5, &motor_addr);
-    simu.step();
+    simu.process_event(Motor::load, 0.5, &motor_addr)?;
+    simu.step()?;
     t += Duration::new(0, 100_000_000);
 
     // The motor should start moving again, but since the phase was incremented
@@ -287,7 +286,7 @@ fn main() {
 
     // Advance simulation time by 0.7s, which with a 10Hz PPS should correspond to
     // 7 position increments.
-    simu.step_by(Duration::new(0, 700_000_000));
+    simu.step_until(Duration::new(0, 700_000_000))?;
     t += Duration::new(0, 700_000_000);
     assert_eq!(simu.time(), t);
     for _ in 0..7 {
@@ -298,8 +297,8 @@ fn main() {
 
     // Now make the motor rotate in the opposite direction. Note that this
     // driver only accounts for a new PPS at the next pulse.
-    simu.send_event(Driver::pulse_rate, -10.0, &driver_addr);
-    simu.step();
+    simu.process_event(Driver::pulse_rate, -10.0, &driver_addr)?;
+    simu.step()?;
     t += Duration::new(0, 100_000_000);
     assert_eq!(simu.time(), t);
     pos = (pos + 1) % Motor::STEPS_PER_REV;
@@ -307,9 +306,11 @@ fn main() {
 
     // Advance simulation time by 1.9s, which with a -10Hz PPS should correspond
     // to 19 position decrements.
-    simu.step_by(Duration::new(1, 900_000_000));
+    simu.step_until(Duration::new(1, 900_000_000))?;
     t += Duration::new(1, 900_000_000);
     assert_eq!(simu.time(), t);
     pos = (pos + Motor::STEPS_PER_REV - 19) % Motor::STEPS_PER_REV;
     assert_eq!(position.by_ref().last(), Some(pos));
+
+    Ok(())
 }

nexosim/src/channel.rs

@@ -4,11 +4,11 @@
 
 mod queue;
 
+use std::cell::Cell;
 use std::error;
 use std::fmt;
 use std::future::Future;
 use std::marker::PhantomData;
-use std::num::NonZeroUsize;
 use std::sync::atomic::{self, AtomicUsize, Ordering};
 use std::sync::Arc;
 
@@ -19,8 +19,15 @@ use recycle_box::RecycleBox;
 use queue::{PopError, PushError, Queue};
 use recycle_box::coerce_box;
 
-use crate::model::Model;
-use crate::time::Scheduler;
+use crate::model::{Context, Model};
+
+// Counts the difference between the number of sent and received messages for
+// this thread.
+//
+// This is used by the executor to make sure that all messages have been
+// received upon completion of a simulation step, i.e. that no deadlock
+// occurred.
+thread_local! { pub(crate) static THREAD_MSG_COUNT: Cell<isize> = const { Cell::new(0) }; }
 
 /// Data shared between the receiver and the senders.
 struct Inner<M> {
@@ -46,7 +53,7 @@ impl<M: 'static> Inner<M> {
 }
 
 /// A receiver which can asynchronously execute `async` message that take an
-/// argument of type `&mut M` and an optional `&Scheduler<M>` argument.
+/// argument of type `&mut M` and an optional `&mut Context<M>` argument.
 pub(crate) struct Receiver<M> {
     /// Shared data.
     inner: Arc<Inner<M>>,
@@ -86,12 +93,19 @@ impl<M: Model> Receiver<M> {
         }
     }
 
+    /// Creates a new observer.
+    pub(crate) fn observer(&self) -> impl ChannelObserver {
+        Observer {
+            inner: self.inner.clone(),
+        }
+    }
+
     /// Receives and executes a message asynchronously, if necessary waiting
     /// until one becomes available.
     pub(crate) async fn recv(
         &mut self,
         model: &mut M,
-        scheduler: &Scheduler<M>,
+        cx: &mut Context<M>,
     ) -> Result<(), RecvError> {
         let msg = unsafe {
             self.inner
@@ -106,12 +120,16 @@ impl<M: Model> Receiver<M> {
 
         match msg {
             Some(mut msg) => {
-                // Consume the message to obtain a boxed future.
-                let fut = msg.call_once(model, scheduler, self.future_box.take().unwrap());
+                // Decrement the count of in-flight messages.
+                THREAD_MSG_COUNT.set(THREAD_MSG_COUNT.get().wrapping_sub(1));
 
-                // Now that `msg` was consumed and its slot in the queue was
-                // freed, signal to one awaiting sender that one slot is
+                // Take the message to obtain a boxed future.
+                let fut = msg.call_once(model, cx, self.future_box.take().unwrap());
+
+                // Now that the message was taken, drop `msg` to free its slot
+                // in the queue and signal to one awaiting sender that a slot is
                 // available for sending.
+                drop(msg);
                 self.inner.sender_signal.notify_one();
 
                 // Await the future provided by the message.
@@ -154,7 +172,7 @@ impl<M: Model> Receiver<M> {
     /// time, but an identifier may be reused after all handles to a channel
     /// have been dropped.
     pub(crate) fn channel_id(&self) -> ChannelId {
-        ChannelId(NonZeroUsize::new(&*self.inner as *const Inner<M> as usize).unwrap())
+        ChannelId(&*self.inner as *const Inner<M> as usize)
     }
 }
 
@@ -189,7 +207,7 @@ impl<M: Model> Sender<M> {
     where
         F: for<'a> FnOnce(
                 &'a mut M,
-                &'a Scheduler<M>,
+                &'a mut Context<M>,
                 RecycleBox<()>,
             ) -> RecycleBox<dyn Future<Output = ()> + Send + 'a>
             + Send
@@ -221,6 +239,9 @@ impl<M: Model> Sender<M> {
         if success {
             self.inner.receiver_signal.notify();
 
+            // Increment the count of in-flight messages.
+            THREAD_MSG_COUNT.set(THREAD_MSG_COUNT.get().wrapping_add(1));
+
             Ok(())
         } else {
             Err(SendError)
@@ -255,8 +276,8 @@ impl<M: Model> Sender<M> {
     /// All channels are guaranteed to have different identifiers at any given
     /// time, but an identifier may be reused after all handles to a channel
     /// have been dropped.
-    pub(crate) fn channel_id(&self) -> ChannelId {
-        ChannelId(NonZeroUsize::new(&*self.inner as *const Inner<M> as usize).unwrap())
+    pub(crate) fn channel_id(&self) -> usize {
+        Arc::as_ptr(&self.inner) as usize
     }
 }
 
@@ -277,6 +298,37 @@ impl<M> Clone for Sender<M> {
     }
 }
 
+/// A model-independent handle to a channel that can observe the current number
+/// of messages.
+pub(crate) trait ChannelObserver: Send {
+    /// Returns the current number of messages in the channel.
+    ///
+    /// # Warning
+    ///
+    /// The returned result is only meaningful if it can be established than
+    /// there are no concurrent send or receive operations on the channel.
+    /// Otherwise, the returned value may neither reflect the current state nor
+    /// the past state of the channel, and may be greater than the capacity of
+    /// the channel.
+    fn len(&self) -> usize;
+}
+
+/// A handle to a channel that can observe the current number of messages.
+///
+/// Multiple [`Observer`]s can be created using the [`Receiver::observer`]
+/// method or via cloning.
+#[derive(Clone)]
+pub(crate) struct Observer<M: 'static> {
+    /// Shared data.
+    inner: Arc<Inner<M>>,
+}
+
+impl<M: Model> ChannelObserver for Observer<M> {
+    fn len(&self) -> usize {
+        self.inner.queue.len()
+    }
+}
+
 impl<M: 'static> Drop for Sender<M> {
     fn drop(&mut self) {
         // Decrease the reference count of senders.
@@ -312,7 +364,7 @@ impl<M> fmt::Debug for Sender<M> {
 }
 
 /// A closure that can be called once to create a future boxed in a `RecycleBox`
-/// from an `&mut M`, a `&Scheduler<M>` and an empty `RecycleBox`.
+/// from an `&mut M`, a `&mut Context<M>` and an empty `RecycleBox`.
 ///
 /// This is basically a workaround to emulate an `FnOnce` with the equivalent of
 /// an `FnMut` so that it is possible to call it as a `dyn` trait stored in a
@@ -328,7 +380,7 @@ trait MessageFn<M: Model>: Send {
     fn call_once<'a>(
         &mut self,
         model: &'a mut M,
-        scheduler: &'a Scheduler<M>,
+        cx: &'a mut Context<M>,
         recycle_box: RecycleBox<()>,
     ) -> RecycleBox<dyn Future<Output = ()> + Send + 'a>;
 }
@@ -350,7 +402,7 @@ impl<F, M: Model> MessageFn<M> for MessageFnOnce<F, M>
 where
     F: for<'a> FnOnce(
             &'a mut M,
-            &'a Scheduler<M>,
+            &'a mut Context<M>,
             RecycleBox<()>,
         ) -> RecycleBox<dyn Future<Output = ()> + Send + 'a>
         + Send,
@@ -358,18 +410,18 @@ where
     fn call_once<'a>(
         &mut self,
         model: &'a mut M,
-        scheduler: &'a Scheduler<M>,
+        cx: &'a mut Context<M>,
         recycle_box: RecycleBox<()>,
     ) -> RecycleBox<dyn Future<Output = ()> + Send + 'a> {
         let closure = self.msg_fn.take().unwrap();
 
-        (closure)(model, scheduler, recycle_box)
+        (closure)(model, cx, recycle_box)
     }
 }
 
 /// Unique identifier for a channel.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
-pub(crate) struct ChannelId(NonZeroUsize);
+pub(crate) struct ChannelId(usize);
 
 impl fmt::Display for ChannelId {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

nexosim/src/channel/queue.rs

@@ -33,7 +33,7 @@ pub(super) struct MessageBorrow<'a, T: ?Sized> {
     stamp: usize,
 }
 
-impl<'a, T: ?Sized> Deref for MessageBorrow<'a, T> {
+impl<T: ?Sized> Deref for MessageBorrow<'_, T> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
@@ -41,13 +41,13 @@ impl<'a, T: ?Sized> Deref for MessageBorrow<'a, T> {
     }
 }
 
-impl<'a, T: ?Sized> DerefMut for MessageBorrow<'a, T> {
+impl<T: ?Sized> DerefMut for MessageBorrow<'_, T> {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.msg
     }
 }
 
-impl<'a, T: ?Sized> Drop for MessageBorrow<'a, T> {
+impl<T: ?Sized> Drop for MessageBorrow<'_, T> {
     fn drop(&mut self) {
         let slot = &self.queue.buffer[self.index];
 
@@ -67,7 +67,7 @@ impl<'a, T: ?Sized> Drop for MessageBorrow<'a, T> {
         slot.stamp.store(self.stamp, Ordering::Release);
     }
 }
-impl<'a, M> fmt::Debug for MessageBorrow<'a, M> {
+impl<M> fmt::Debug for MessageBorrow<'_, M> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("MessageBorrow").finish_non_exhaustive()
     }
@@ -85,7 +85,7 @@ struct Slot<T: ?Sized> {
     message: UnsafeCell<MessageBox<T>>,
 }
 
-/// An fast MPSC queue that stores its items in recyclable boxes.
+/// A fast MPSC queue that stores its items in recyclable boxes.
 ///
 /// The item may be unsized.
 ///
@@ -122,7 +122,7 @@ pub(super) struct Queue<T: ?Sized> {
     /// and the producer. The reason it is shared is that the drop handler of
     /// the last `Inner` owner (which may be a producer) needs access to the
     /// dequeue position.
-    dequeue_pos: CachePadded<UnsafeCell<usize>>,
+    dequeue_pos: CachePadded<AtomicUsize>,
 
     /// Buffer holding the closures and their stamps.
     buffer: Box<[Slot<T>]>,
@@ -160,7 +160,7 @@ impl<T: ?Sized> Queue<T> {
 
         Queue {
             enqueue_pos: CachePadded::new(AtomicUsize::new(0)),
-            dequeue_pos: CachePadded::new(UnsafeCell::new(0)),
+            dequeue_pos: CachePadded::new(AtomicUsize::new(0)),
             buffer: buffer.into(),
             right_mask,
             closed_channel_mask,
@@ -241,7 +241,7 @@ impl<T: ?Sized> Queue<T> {
     ///
     /// This method may not be called concurrently from multiple threads.
     pub(super) unsafe fn pop(&self) -> Result<MessageBorrow<'_, T>, PopError> {
-        let dequeue_pos = self.dequeue_pos.with(|p| *p);
+        let dequeue_pos = self.dequeue_pos.load(Ordering::Relaxed);
         let index = dequeue_pos & self.right_mask;
         let slot = &self.buffer[index];
         let stamp = slot.stamp.load(Ordering::Acquire);
@@ -251,10 +251,10 @@ impl<T: ?Sized> Queue<T> {
             // closure can be popped.
             debug_or_loom_assert_eq!(stamp, dequeue_pos + 1);
 
-            // Only this thread can access the dequeue position so there is no
+            // Only this thread can modify the dequeue position so there is no
             // need to increment the position atomically with a `fetch_add`.
             self.dequeue_pos
-                .with_mut(|p| *p = self.next_queue_pos(dequeue_pos));
+                .store(self.next_queue_pos(dequeue_pos), Ordering::Relaxed);
 
             // Extract the closure from the slot and set the stamp to the value of
             // the dequeue position increased by one sequence increment.
@@ -318,6 +318,30 @@ impl<T: ?Sized> Queue<T> {
         self.enqueue_pos.load(Ordering::Relaxed) & self.closed_channel_mask != 0
     }
 
+    /// Returns the number of items in the queue.
+    ///
+    /// # Warning
+    ///
+    /// While this method is safe by Rust's standard, the returned result is
+    /// only meaningful if it can be established than there are no concurrent
+    /// `push` or `pop` operations. Otherwise, the returned value may neither
+    /// reflect the current state nor the past state of the queue, and may be
+    /// greater than the capacity of the queue.
+    pub(super) fn len(&self) -> usize {
+        let enqueue_pos = self.enqueue_pos.load(Ordering::Relaxed);
+        let dequeue_pos = self.dequeue_pos.load(Ordering::Relaxed);
+        let enqueue_idx = enqueue_pos & (self.right_mask >> 1);
+        let dequeue_idx = dequeue_pos & (self.right_mask >> 1);
+
+        // Establish whether the sequence numbers of the enqueue and dequeue
+        // positions differ. If yes, it means the enqueue position has wrapped
+        // around one more time so the difference between indices must be
+        // increased by the buffer capacity.
+        let carry_flag = (enqueue_pos & !self.right_mask) != (dequeue_pos & !self.right_mask);
+
+        (enqueue_idx + (carry_flag as usize) * self.buffer.len()) - dequeue_idx
+    }
+
     /// Increment the queue position, incrementing the sequence count as well if
     /// the index wraps to 0.
     ///
@@ -389,7 +413,7 @@ impl<T: ?Sized> Producer<T> {
     }
 
     /// Checks if the queue is closed.
-    #[cfg(not(asynchronix_loom))]
+    #[cfg(not(nexosim_loom))]
     fn is_closed(&self) -> bool {
         self.inner.is_closed()
     }
@@ -423,6 +447,12 @@ impl<T: ?Sized> Consumer<T> {
     fn close(&self) {
         self.inner.close();
     }
+
+    /// Returns the number of items.
+    #[cfg(not(nexosim_loom))]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
 }
 
 #[cfg(test)]
@@ -440,7 +470,7 @@ fn queue<T: ?Sized>(capacity: usize) -> (Producer<T>, Consumer<T>) {
 }
 
 /// Regular tests.
-#[cfg(all(test, not(asynchronix_loom)))]
+#[cfg(all(test, not(nexosim_loom)))]
 mod tests {
     use super::*;
 
@@ -452,7 +482,7 @@ mod tests {
 
         assert!(matches!(c.pop(), Err(PopError::Empty)));
 
-        assert!(matches!(p.push(|b| RecycleBox::recycle(b, 42)), Ok(_)));
+        assert!(p.push(|b| RecycleBox::recycle(b, 42)).is_ok());
         p.close();
 
         assert_eq!(*c.pop().unwrap(), 42);
@@ -463,12 +493,12 @@ mod tests {
     fn queue_closed_by_consumer() {
         let (p, mut c) = queue(3);
 
-        assert_eq!(p.is_closed(), false);
-        assert!(matches!(p.push(|b| RecycleBox::recycle(b, 42)), Ok(_)));
+        assert!(!p.is_closed());
+        assert!(p.push(|b| RecycleBox::recycle(b, 42)).is_ok());
 
         c.close();
 
-        assert_eq!(p.is_closed(), true);
+        assert!(p.is_closed());
         assert!(matches!(
             p.push(|b| RecycleBox::recycle(b, 13)),
             Err(PushError::Closed)
@@ -569,10 +599,56 @@ mod tests {
     fn queue_mpsc_capacity_three() {
         queue_mpsc(3);
     }
+
+    #[test]
+    fn queue_len() {
+        let (p, mut c) = queue(4);
+
+        let _ = p.push(|b| RecycleBox::recycle(b, 0));
+        assert_eq!(c.len(), 1);
+        let _ = p.push(|b| RecycleBox::recycle(b, 1));
+        assert_eq!(c.len(), 2);
+        let _ = c.pop();
+        assert_eq!(c.len(), 1);
+        let _ = p.push(|b| RecycleBox::recycle(b, 2));
+        assert_eq!(c.len(), 2);
+        let _ = p.push(|b| RecycleBox::recycle(b, 3));
+        assert_eq!(c.len(), 3);
+        let _ = c.pop();
+        assert_eq!(c.len(), 2);
+        let _ = p.push(|b| RecycleBox::recycle(b, 4));
+        assert_eq!(c.len(), 3);
+        let _ = c.pop();
+        assert_eq!(c.len(), 2);
+        let _ = p.push(|b| RecycleBox::recycle(b, 5));
+        assert_eq!(c.len(), 3);
+        let _ = p.push(|b| RecycleBox::recycle(b, 6));
+        assert_eq!(c.len(), 4);
+        let _ = c.pop();
+        assert_eq!(c.len(), 3);
+        let _ = p.push(|b| RecycleBox::recycle(b, 7));
+        assert_eq!(c.len(), 4);
+        let _ = c.pop();
+        assert_eq!(c.len(), 3);
+        let _ = p.push(|b| RecycleBox::recycle(b, 8));
+        assert_eq!(c.len(), 4);
+        let _ = c.pop();
+        assert_eq!(c.len(), 3);
+        let _ = p.push(|b| RecycleBox::recycle(b, 9));
+        assert_eq!(c.len(), 4);
+        let _ = c.pop();
+        assert_eq!(c.len(), 3);
+        let _ = c.pop();
+        assert_eq!(c.len(), 2);
+        let _ = c.pop();
+        assert_eq!(c.len(), 1);
+        let _ = c.pop();
+        assert_eq!(c.len(), 0);
+    }
 }
 
 /// Loom tests.
-#[cfg(all(test, asynchronix_loom))]
+#[cfg(all(test, nexosim_loom))]
 mod tests {
     use super::*;
 

nexosim/src/dev_hooks.rs

@@ -3,6 +3,7 @@
 //! Not for production use!
 
 use std::future::Future;
+use std::time::Duration;
 
 use crate::executor;
 
@@ -15,7 +16,18 @@ impl Executor {
     ///
     /// The maximum number of threads is set with the `pool_size` parameter.
     pub fn new(pool_size: usize) -> Self {
-        Self(executor::Executor::new(pool_size))
+        let dummy_cx = crate::executor::SimulationContext {
+            #[cfg(feature = "tracing")]
+            time_reader: crate::util::sync_cell::SyncCell::new(
+                crate::time::TearableAtomicTime::new(crate::time::MonotonicTime::EPOCH),
+            )
+            .reader(),
+        };
+        Self(executor::Executor::new_multi_threaded(
+            pool_size,
+            dummy_cx,
+            executor::Signal::new(),
+        ))
     }
 
     /// Spawns a task which output will never be retrieved.
@@ -33,6 +45,6 @@ impl Executor {
     /// Let the executor run, blocking until all futures have completed or until
     /// the executor deadlocks.
     pub fn run(&mut self) {
-        self.0.run();
+        self.0.run(Duration::ZERO).unwrap();
     }
 }

nexosim/src/executor.rs

@@ -0,0 +1,257 @@
+//! `async` executor trait.
+
+mod mt_executor;
+mod st_executor;
+mod task;
+
+use std::any::Any;
+use std::future::Future;
+use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
+use std::sync::Arc;
+use std::time::Duration;
+
+use crossbeam_utils::CachePadded;
+
+use crate::macros::scoped_thread_local::scoped_thread_local;
+use crate::simulation::ModelId;
+#[cfg(feature = "tracing")]
+use crate::time::AtomicTimeReader;
+use task::Promise;
+
+/// Unique identifier for executor instances.
+static NEXT_EXECUTOR_ID: AtomicUsize = AtomicUsize::new(0);
+
+#[derive(Debug)]
+pub(crate) enum ExecutorError {
+    /// Not all messages have been processed.
+    UnprocessedMessages(usize),
+    /// The simulation has timed out.
+    Timeout,
+    /// The simulation has panicked.
+    Panic(ModelId, Box<dyn Any + Send + 'static>),
+}
+
+/// Context common to all executor types.
+#[derive(Clone)]
+pub(crate) struct SimulationContext {
+    /// Read-only handle to the simulation time.
+    #[cfg(feature = "tracing")]
+    pub(crate) time_reader: AtomicTimeReader,
+}
+
+scoped_thread_local!(pub(crate) static SIMULATION_CONTEXT: SimulationContext);
+
+/// A single-threaded or multi-threaded `async` executor.
+#[derive(Debug)]
+pub(crate) enum Executor {
+    StExecutor(st_executor::Executor),
+    MtExecutor(mt_executor::Executor),
+}
+
+impl Executor {
+    /// Creates an executor that runs futures on the current thread.
+    pub(crate) fn new_single_threaded(
+        simulation_context: SimulationContext,
+        abort_signal: Signal,
+    ) -> Self {
+        Self::StExecutor(st_executor::Executor::new(simulation_context, abort_signal))
+    }
+
+    /// Creates an executor that runs futures on a thread pool.
+    ///
+    /// The maximum number of threads is set with the `num_threads` parameter.
+    ///
+    /// # Panics
+    ///
+    /// This will panic if the specified number of threads is zero or more than
+    /// `usize::BITS`.
+    pub(crate) fn new_multi_threaded(
+        num_threads: usize,
+        simulation_context: SimulationContext,
+        abort_signal: Signal,
+    ) -> Self {
+        Self::MtExecutor(mt_executor::Executor::new(
+            num_threads,
+            simulation_context,
+            abort_signal,
+        ))
+    }
+
+    /// Spawns a task which output will never be retrieved.
+    ///
+    /// Note that spawned tasks are not executed until [`run`](Executor::run) is
+    /// called.
+    #[allow(unused)]
+    pub(crate) fn spawn<T>(&self, future: T) -> Promise<T::Output>
+    where
+        T: Future + Send + 'static,
+        T::Output: Send + 'static,
+    {
+        match self {
+            Self::StExecutor(executor) => executor.spawn(future),
+            Self::MtExecutor(executor) => executor.spawn(future),
+        }
+    }
+
+    /// Spawns a task which output will never be retrieved.
+    ///
+    /// Note that spawned tasks are not executed until [`run`](Executor::run) is
+    /// called.
+    pub(crate) fn spawn_and_forget<T>(&self, future: T)
+    where
+        T: Future + Send + 'static,
+        T::Output: Send + 'static,
+    {
+        match self {
+            Self::StExecutor(executor) => executor.spawn_and_forget(future),
+            Self::MtExecutor(executor) => executor.spawn_and_forget(future),
+        }
+    }
+
+    /// Execute spawned tasks, blocking until all futures have completed or
+    /// until the executor reaches a deadlock.
+    pub(crate) fn run(&mut self, timeout: Duration) -> Result<(), ExecutorError> {
+        match self {
+            Self::StExecutor(executor) => executor.run(timeout),
+            Self::MtExecutor(executor) => executor.run(timeout),
+        }
+    }
+}
+
+/// A single-use shared boolean signal.
+#[derive(Clone, Debug)]
+pub(crate) struct Signal(Arc<CachePadded<AtomicBool>>);
+
+impl Signal {
+    /// Create a new, cleared signal.
+    pub(crate) fn new() -> Self {
+        Self(Arc::new(CachePadded::new(AtomicBool::new(false))))
+    }
+
+    /// Sets the signal.
+    pub(crate) fn set(&self) {
+        self.0.store(true, Ordering::Relaxed);
+    }
+
+    /// Returns `true``is the signal was set.
+    pub(crate) fn is_set(&self) -> bool {
+        self.0.load(Ordering::Relaxed)
+    }
+}
+
+#[cfg(all(test, not(nexosim_loom)))]
+mod tests {
+    use std::sync::atomic::Ordering;
+    use std::sync::Arc;
+
+    use futures_channel::mpsc;
+    use futures_util::StreamExt;
+
+    use super::*;
+
+    fn dummy_simulation_context() -> SimulationContext {
+        SimulationContext {
+            #[cfg(feature = "tracing")]
+            time_reader: crate::util::sync_cell::SyncCell::new(
+                crate::time::TearableAtomicTime::new(crate::time::MonotonicTime::EPOCH),
+            )
+            .reader(),
+        }
+    }
+
+    /// An object that runs an arbitrary closure when dropped.
+    struct RunOnDrop<F: FnOnce()> {
+        drop_fn: Option<F>,
+    }
+    impl<F: FnOnce()> RunOnDrop<F> {
+        /// Creates a new `RunOnDrop`.
+        fn new(drop_fn: F) -> Self {
+            Self {
+                drop_fn: Some(drop_fn),
+            }
+        }
+    }
+    impl<F: FnOnce()> Drop for RunOnDrop<F> {
+        fn drop(&mut self) {
+            if let Some(f) = self.drop_fn.take() {
+                f()
+            }
+        }
+    }
+
+    fn executor_drop_cycle(mut executor: Executor) {
+        let (sender1, mut receiver1) = mpsc::channel(2);
+        let (sender2, mut receiver2) = mpsc::channel(2);
+        let (sender3, mut receiver3) = mpsc::channel(2);
+
+        let drop_count = Arc::new(AtomicUsize::new(0));
+
+        // Spawn 3 tasks that wake one another when dropped.
+        executor.spawn_and_forget({
+            let mut sender2 = sender2.clone();
+            let mut sender3 = sender3.clone();
+            let drop_count = drop_count.clone();
+
+            async move {
+                let _guard = RunOnDrop::new(move || {
+                    let _ = sender2.try_send(());
+                    let _ = sender3.try_send(());
+                    drop_count.fetch_add(1, Ordering::Relaxed);
+                });
+                let _ = receiver1.next().await;
+            }
+        });
+        executor.spawn_and_forget({
+            let mut sender1 = sender1.clone();
+            let mut sender3 = sender3.clone();
+            let drop_count = drop_count.clone();
+
+            async move {
+                let _guard = RunOnDrop::new(move || {
+                    let _ = sender1.try_send(());
+                    let _ = sender3.try_send(());
+                    drop_count.fetch_add(1, Ordering::Relaxed);
+                });
+                let _ = receiver2.next().await;
+            }
+        });
+        executor.spawn_and_forget({
+            let mut sender1 = sender1.clone();
+            let mut sender2 = sender2.clone();
+            let drop_count = drop_count.clone();
+
+            async move {
+                let _guard = RunOnDrop::new(move || {
+                    let _ = sender1.try_send(());
+                    let _ = sender2.try_send(());
+                    drop_count.fetch_add(1, Ordering::Relaxed);
+                });
+                let _ = receiver3.next().await;
+            }
+        });
+
+        executor.run(Duration::ZERO).unwrap();
+
+        // Make sure that all tasks are eventually dropped even though each task
+        // wakes the others when dropped.
+        drop(executor);
+        assert_eq!(drop_count.load(Ordering::Relaxed), 3);
+    }
+
+    #[test]
+    fn executor_drop_cycle_st() {
+        executor_drop_cycle(Executor::new_single_threaded(
+            dummy_simulation_context(),
+            Signal::new(),
+        ));
+    }
+
+    #[test]
+    fn executor_drop_cycle_mt() {
+        executor_drop_cycle(Executor::new_multi_threaded(
+            3,
+            dummy_simulation_context(),
+            Signal::new(),
+        ));
+    }
+}

nexosim/src/executor/mt_executor.rs

@@ -41,37 +41,36 @@
 //! notification flag, thus alleviating the need to reset the notification flag
 //! before polling a future.
 
+mod injector;
+mod pool_manager;
+
+use std::cell::Cell;
 use std::fmt;
 use std::future::Future;
 use std::panic::{self, AssertUnwindSafe};
-use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::atomic::{AtomicIsize, Ordering};
 use std::sync::{Arc, Mutex};
 use std::thread::{self, JoinHandle};
 use std::time::{Duration, Instant};
 
-use crossbeam_utils::sync::{Parker, Unparker};
+// TODO: revert to `crossbeam_utils::sync::Parker` once timeout support lands in
+// v1.0 (see https://github.com/crossbeam-rs/crossbeam/pull/1012).
+use parking::{Parker, Unparker};
 use slab::Slab;
 
-mod injector;
-mod pool_manager;
-mod task;
-mod worker;
-
-#[cfg(all(test, not(asynchronix_loom)))]
-mod tests;
-
+use crate::channel;
+use crate::executor::task::{self, CancelToken, Promise, Runnable};
+use crate::executor::{
+    ExecutorError, Signal, SimulationContext, NEXT_EXECUTOR_ID, SIMULATION_CONTEXT,
+};
 use crate::macros::scoped_thread_local::scoped_thread_local;
+use crate::simulation::CURRENT_MODEL_ID;
 use crate::util::rng::Rng;
-
-use self::pool_manager::PoolManager;
-use self::task::{CancelToken, Promise, Runnable};
-use self::worker::Worker;
+use pool_manager::PoolManager;
 
 const BUCKET_SIZE: usize = 128;
 const QUEUE_SIZE: usize = BUCKET_SIZE * 2;
 
-static NEXT_EXECUTOR_ID: AtomicUsize = AtomicUsize::new(0);
-
 type Bucket = injector::Bucket<Runnable, BUCKET_SIZE>;
 type Injector = injector::Injector<Runnable, BUCKET_SIZE>;
 type LocalQueue = st3::fifo::Worker<Runnable>;
@@ -88,8 +87,10 @@ pub(crate) struct Executor {
     active_tasks: Arc<Mutex<Slab<CancelToken>>>,
     /// Parker for the main executor thread.
     parker: Parker,
-    /// Join handles of the worker threads.
+    /// Handles to the worker threads.
     worker_handles: Vec<JoinHandle<()>>,
+    /// Handle to the forced termination signal.
+    abort_signal: Signal,
 }
 
 impl Executor {
@@ -101,7 +102,11 @@ impl Executor {
     ///
     /// This will panic if the specified number of threads is zero or is more
     /// than `usize::BITS`.
-    pub(crate) fn new(num_threads: usize) -> Self {
+    pub(crate) fn new(
+        num_threads: usize,
+        simulation_context: SimulationContext,
+        abort_signal: Signal,
+    ) -> Self {
         let parker = Parker::new();
         let unparker = parker.unparker().clone();
 
@@ -147,11 +152,17 @@ impl Executor {
                     .spawn({
                         let context = context.clone();
                         let active_tasks = active_tasks.clone();
+                        let simulation_context = simulation_context.clone();
+                        let abort_signal = abort_signal.clone();
+
                         move || {
                             let worker = Worker::new(local_queue, context);
-                            ACTIVE_TASKS.set(&active_tasks, || {
-                                LOCAL_WORKER
-                                    .set(&worker, || run_local_worker(&worker, id, worker_parker))
+                            SIMULATION_CONTEXT.set(&simulation_context, || {
+                                ACTIVE_TASKS.set(&active_tasks, || {
+                                    LOCAL_WORKER.set(&worker, || {
+                                        run_local_worker(&worker, id, worker_parker, abort_signal)
+                                    })
+                                })
                             });
                         }
                     })
@@ -168,15 +179,15 @@ impl Executor {
             active_tasks,
             parker,
             worker_handles,
+            abort_signal,
         }
     }
 
     /// Spawns a task and returns a promise that can be polled to retrieve the
     /// task's output.
     ///
-    /// Note that spawned tasks are not executed until [`run()`](Executor::run)
-    /// is called.
-    #[allow(unused)]
+    /// Note that spawned tasks are not executed until [`run`](Executor::run) is
+    /// called.
     pub(crate) fn spawn<T>(&self, future: T) -> Promise<T::Output>
     where
         T: Future + Send + 'static,
@@ -204,8 +215,8 @@ impl Executor {
     /// This is mostly useful to avoid undue reference counting for futures that
     /// return a `()` type.
     ///
-    /// Note that spawned tasks are not executed until [`run()`](Executor::run)
-    /// is called.
+    /// Note that spawned tasks are not executed until [`run`](Executor::run) is
+    /// called.
     pub(crate) fn spawn_and_forget<T>(&self, future: T)
     where
         T: Future + Send + 'static,
@@ -226,20 +237,37 @@ impl Executor {
         self.context.injector.insert_task(runnable);
     }
 
-    /// Execute spawned tasks, blocking until all futures have completed or
-    /// until the executor reaches a deadlock.
-    pub(crate) fn run(&mut self) {
+    /// Execute spawned tasks, blocking until all futures have completed or an
+    /// error is encountered.
+    pub(crate) fn run(&mut self, timeout: Duration) -> Result<(), ExecutorError> {
         self.context.pool_manager.activate_worker();
 
         loop {
-            if let Some(worker_panic) = self.context.pool_manager.take_panic() {
-                panic::resume_unwind(worker_panic);
-            }
-            if self.context.pool_manager.pool_is_idle() {
-                return;
+            if let Some((model_id, payload)) = self.context.pool_manager.take_panic() {
+                return Err(ExecutorError::Panic(model_id, payload));
             }
 
-            self.parker.park();
+            if self.context.pool_manager.pool_is_idle() {
+                let msg_count = self.context.msg_count.load(Ordering::Relaxed);
+                if msg_count != 0 {
+                    let msg_count: usize = msg_count.try_into().unwrap();
+
+                    return Err(ExecutorError::UnprocessedMessages(msg_count));
+                }
+
+                return Ok(());
+            }
+
+            if timeout.is_zero() {
+                self.parker.park();
+            } else if !self.parker.park_timeout(timeout) {
+                // A timeout occurred: request all worker threads to return
+                // as soon as possible.
+                self.abort_signal.set();
+                self.context.pool_manager.activate_all_workers();
+
+                return Err(ExecutorError::Timeout);
+            }
         }
     }
 }
@@ -247,7 +275,8 @@ impl Executor {
 impl Drop for Executor {
     fn drop(&mut self) {
         // Force all threads to return.
-        self.context.pool_manager.trigger_termination();
+        self.abort_signal.set();
+        self.context.pool_manager.activate_all_workers();
         for handle in self.worker_handles.drain(0..) {
             handle.join().unwrap();
         }
@@ -295,12 +324,18 @@ impl fmt::Debug for Executor {
 struct ExecutorContext {
     /// Injector queue.
     injector: Injector,
-    /// Unique executor ID inherited by all tasks spawned on this executor instance.
+    /// Unique executor identifier inherited by all tasks spawned on this
+    /// executor instance.
     executor_id: usize,
     /// Unparker for the main executor thread.
     executor_unparker: Unparker,
     /// Manager for all worker threads.
     pool_manager: PoolManager,
+    /// Difference between the number of sent and received messages.
+    ///
+    /// This counter is only updated by worker threads before they park and is
+    /// therefore only consistent once all workers are parked.
+    msg_count: AtomicIsize,
 }
 
 impl ExecutorContext {
@@ -323,6 +358,7 @@ impl ExecutorContext {
                 stealers.into_boxed_slice(),
                 worker_unparkers,
             ),
+            msg_count: AtomicIsize::new(0),
         }
     }
 }
@@ -374,6 +410,24 @@ impl<T: Future> Drop for CancellableFuture<T> {
     }
 }
 
+/// A local worker with access to global executor resources.
+pub(crate) struct Worker {
+    local_queue: LocalQueue,
+    fast_slot: Cell<Option<Runnable>>,
+    executor_context: Arc<ExecutorContext>,
+}
+
+impl Worker {
+    /// Creates a new worker.
+    fn new(local_queue: LocalQueue, executor_context: Arc<ExecutorContext>) -> Self {
+        Self {
+            local_queue,
+            fast_slot: Cell::new(None),
+            executor_context,
+        }
+    }
+}
+
 /// Schedules a `Runnable` from within a worker thread.
 ///
 /// # Panics
@@ -434,13 +488,22 @@ fn schedule_task(task: Runnable, executor_id: usize) {
 /// is received or until it panics.
 ///
 /// Panics caught in this thread are relayed to the main executor thread.
-fn run_local_worker(worker: &Worker, id: usize, parker: Parker) {
+fn run_local_worker(worker: &Worker, id: usize, parker: Parker, abort_signal: Signal) {
     let pool_manager = &worker.executor_context.pool_manager;
     let injector = &worker.executor_context.injector;
     let executor_unparker = &worker.executor_context.executor_unparker;
     let local_queue = &worker.local_queue;
     let fast_slot = &worker.fast_slot;
 
+    // Update the global message counter.
+    let update_msg_count = || {
+        let thread_msg_count = channel::THREAD_MSG_COUNT.replace(0);
+        worker
+            .executor_context
+            .msg_count
+            .fetch_add(thread_msg_count, Ordering::Relaxed);
+    };
+
     let result = panic::catch_unwind(AssertUnwindSafe(|| {
         // Set how long to spin when searching for a task.
         const MAX_SEARCH_DURATION: Duration = Duration::from_nanos(1000);
@@ -453,9 +516,10 @@ fn run_local_worker(worker: &Worker, id: usize, parker: Parker) {
 
             // Try to deactivate the worker.
             if pool_manager.try_set_worker_inactive(id) {
-                parker.park();
                 // No need to call `begin_worker_search()`: this was done by the
                 // thread that unparked the worker.
+                update_msg_count();
+                parker.park();
             } else if injector.is_empty() {
                 // This worker could not be deactivated because it was the last
                 // active worker. In such case, the call to
@@ -464,6 +528,7 @@ fn run_local_worker(worker: &Worker, id: usize, parker: Parker) {
                 // not activate a new worker, which is why some tasks may now be
                 // visible in the injector queue.
                 pool_manager.set_all_workers_inactive();
+                update_msg_count();
                 executor_unparker.unpark();
                 parker.park();
                 // No need to call `begin_worker_search()`: this was done by the
@@ -472,7 +537,7 @@ fn run_local_worker(worker: &Worker, id: usize, parker: Parker) {
                 pool_manager.begin_worker_search();
             }
 
-            if pool_manager.termination_is_triggered() {
+            if abort_signal.is_set() {
                 return;
             }
 
@@ -542,7 +607,7 @@ fn run_local_worker(worker: &Worker, id: usize, parker: Parker) {
 
                 // Pop tasks from the fast slot or the local queue.
                 while let Some(task) = fast_slot.take().or_else(|| local_queue.pop()) {
-                    if pool_manager.termination_is_triggered() {
+                    if abort_signal.is_set() {
                         return;
                     }
                     task.run();
@@ -555,10 +620,12 @@ fn run_local_worker(worker: &Worker, id: usize, parker: Parker) {
         }
     }));
 
-    // Propagate the panic, if any.
-    if let Err(panic) = result {
-        pool_manager.register_panic(panic);
-        pool_manager.trigger_termination();
+    // Report the panic, if any.
+    if let Err(payload) = result {
+        let model_id = CURRENT_MODEL_ID.take();
+        pool_manager.register_panic(model_id, payload);
+        abort_signal.set();
+        pool_manager.activate_all_workers();
         executor_unparker.unpark();
     }
 }

nexosim/src/executor/mt_executor/pool_manager.rs

@@ -1,10 +1,11 @@
 use std::any::Any;
-use std::sync::atomic::{self, AtomicBool, AtomicUsize, Ordering};
+use std::sync::atomic::{self, AtomicUsize, Ordering};
 use std::sync::Mutex;
 
-use crossbeam_utils::sync::Unparker;
+use parking::Unparker;
 
 use super::Stealer;
+use crate::simulation::ModelId;
 use crate::util::bit;
 use crate::util::rng;
 
@@ -22,13 +23,8 @@ pub(super) struct PoolManager {
     active_workers: AtomicUsize,
     /// Count of all workers currently searching for tasks.
     searching_workers: AtomicUsize,
-    /// Flag requesting all workers to return immediately.
-    terminate_signal: AtomicBool,
     /// Panic caught in a worker thread.
-    worker_panic: Mutex<Option<Box<dyn Any + Send + 'static>>>,
-    #[cfg(feature = "dev-logs")]
-    /// Thread wake-up statistics.
-    record: Record,
+    worker_panic: Mutex<Option<(ModelId, Box<dyn Any + Send + 'static>)>>,
 }
 
 impl PoolManager {
@@ -59,10 +55,7 @@ impl PoolManager {
             worker_unparkers,
             active_workers: AtomicUsize::new(0),
             searching_workers: AtomicUsize::new(0),
-            terminate_signal: AtomicBool::new(false),
             worker_panic: Mutex::new(None),
-            #[cfg(feature = "dev-logs")]
-            record: Record::new(pool_size),
         }
     }
 
@@ -85,8 +78,6 @@ impl PoolManager {
                 .active_workers
                 .fetch_or(1 << first_idle_worker, Ordering::Relaxed);
             if active_workers & (1 << first_idle_worker) == 0 {
-                #[cfg(feature = "dev-logs")]
-                self.record.increment(first_idle_worker);
                 self.begin_worker_search();
                 self.worker_unparkers[first_idle_worker].unpark();
                 return;
@@ -117,8 +108,6 @@ impl PoolManager {
                     .active_workers
                     .fetch_or(1 << first_idle_worker, Ordering::Relaxed);
                 if active_workers & (1 << first_idle_worker) == 0 {
-                    #[cfg(feature = "dev-logs")]
-                    self.record.increment(first_idle_worker);
                     self.begin_worker_search();
                     self.worker_unparkers[first_idle_worker].unpark();
                     return;
@@ -220,36 +209,27 @@ impl PoolManager {
         self.searching_workers.load(Ordering::Relaxed)
     }
 
-    /// Triggers the termination signal and unparks all worker threads so they
-    /// can cleanly terminate.
-    pub(super) fn trigger_termination(&self) {
-        self.terminate_signal.store(true, Ordering::Relaxed);
-
+    /// Unparks all workers and mark them as active.
+    pub(super) fn activate_all_workers(&self) {
         self.set_all_workers_active();
         for unparker in &*self.worker_unparkers {
             unparker.unpark();
         }
     }
 
-    /// Returns true if the termination signal was triggered.
-    pub(super) fn termination_is_triggered(&self) -> bool {
-        self.terminate_signal.load(Ordering::Relaxed)
-    }
-
-    /// Registers a panic associated with the provided worker ID.
+    /// Registers a worker panic.
     ///
-    /// If no panic is currently registered, the panic in argument is
-    /// registered. If a panic was already registered by a worker and was not
-    /// yet processed by the executor, then nothing is done.
-    pub(super) fn register_panic(&self, panic: Box<dyn Any + Send + 'static>) {
+    /// If a panic was already registered and was not yet processed by the
+    /// executor, then nothing is done.
+    pub(super) fn register_panic(&self, model_id: ModelId, payload: Box<dyn Any + Send + 'static>) {
         let mut worker_panic = self.worker_panic.lock().unwrap();
         if worker_panic.is_none() {
-            *worker_panic = Some(panic);
+            *worker_panic = Some((model_id, payload));
         }
     }
 
     /// Takes a worker panic if any is registered.
-    pub(super) fn take_panic(&self) -> Option<Box<dyn Any + Send + 'static>> {
+    pub(super) fn take_panic(&self) -> Option<(ModelId, Box<dyn Any + Send + 'static>)> {
         let mut worker_panic = self.worker_panic.lock().unwrap();
         worker_panic.take()
     }
@@ -273,13 +253,6 @@ impl PoolManager {
     }
 }
 
-#[cfg(feature = "dev-logs")]
-impl Drop for PoolManager {
-    fn drop(&mut self) {
-        println!("Thread launch count: {:?}", self.record.get());
-    }
-}
-
 /// An iterator over active workers that yields their associated stealer,
 /// starting from a randomly selected active worker.
 pub(super) struct ShuffledStealers<'a> {
@@ -346,27 +319,3 @@ impl<'a> Iterator for ShuffledStealers<'a> {
         Some(&self.stealers[current_candidate])
     }
 }
-
-#[cfg(feature = "dev-logs")]
-#[derive(Debug)]
-struct Record {
-    stats: Vec<AtomicUsize>,
-}
-
-#[cfg(feature = "dev-logs")]
-impl Record {
-    fn new(worker_count: usize) -> Self {
-        let mut stats = Vec::new();
-        stats.resize_with(worker_count, Default::default);
-        Self { stats }
-    }
-    fn increment(&self, worker_id: usize) {
-        self.stats[worker_id].fetch_add(1, Ordering::Relaxed);
-    }
-    fn get(&self) -> Vec<usize> {
-        self.stats
-            .iter()
-            .map(|s| s.load(Ordering::Relaxed))
-            .collect()
-    }
-}

nexosim/src/executor/st_executor.rs

@@ -0,0 +1,337 @@
+use std::cell::RefCell;
+use std::future::Future;
+use std::panic::AssertUnwindSafe;
+use std::sync::atomic::Ordering;
+use std::time::Duration;
+use std::{fmt, panic, thread};
+
+// TODO: revert to `crossbeam_utils::sync::Parker` once timeout support lands in
+// v1.0 (see https://github.com/crossbeam-rs/crossbeam/pull/1012).
+use parking::Parker;
+use slab::Slab;
+
+use super::task::{self, CancelToken, Promise, Runnable};
+use super::NEXT_EXECUTOR_ID;
+
+use crate::channel;
+use crate::executor::{ExecutorError, Signal, SimulationContext, SIMULATION_CONTEXT};
+use crate::macros::scoped_thread_local::scoped_thread_local;
+use crate::simulation::CURRENT_MODEL_ID;
+
+const QUEUE_MIN_CAPACITY: usize = 32;
+
+scoped_thread_local!(static EXECUTOR_CONTEXT: ExecutorContext);
+scoped_thread_local!(static ACTIVE_TASKS: RefCell<Slab<CancelToken>>);
+
+/// A single-threaded `async` executor.
+pub(crate) struct Executor {
+    /// Executor state.
+    inner: Option<Box<ExecutorInner>>,
+    /// Handle to the forced termination signal.
+    abort_signal: Signal,
+}
+
+impl Executor {
+    /// Creates an executor that runs futures on the current thread.
+    pub(crate) fn new(simulation_context: SimulationContext, abort_signal: Signal) -> Self {
+        // Each executor instance has a unique ID inherited by tasks to ensure
+        // that tasks are scheduled on their parent executor.
+        let executor_id = NEXT_EXECUTOR_ID.fetch_add(1, Ordering::Relaxed);
+        assert!(
+            executor_id <= usize::MAX / 2,
+            "too many executors have been instantiated"
+        );
+
+        let context = ExecutorContext::new(executor_id);
+        let active_tasks = RefCell::new(Slab::new());
+
+        Self {
+            inner: Some(Box::new(ExecutorInner {
+                context,
+                active_tasks,
+                simulation_context,
+                abort_signal: abort_signal.clone(),
+            })),
+            abort_signal,
+        }
+    }
+
+    /// Spawns a task and returns a promise that can be polled to retrieve the
+    /// task's output.
+    ///
+    /// Note that spawned tasks are not executed until [`run`](Executor::run)
+    /// is called.
+    pub(crate) fn spawn<T>(&self, future: T) -> Promise<T::Output>
+    where
+        T: Future + Send + 'static,
+        T::Output: Send + 'static,
+    {
+        let inner = self.inner.as_ref().unwrap();
+
+        // Book a slot to store the task cancellation token.
+        let mut active_tasks = inner.active_tasks.borrow_mut();
+        let task_entry = active_tasks.vacant_entry();
+
+        // Wrap the future so that it removes its cancel token from the
+        // executor's list when dropped.
+        let future = CancellableFuture::new(future, task_entry.key());
+
+        let (promise, runnable, cancel_token) =
+            task::spawn(future, schedule_task, inner.context.executor_id);
+
+        task_entry.insert(cancel_token);
+        let mut queue = inner.context.queue.borrow_mut();
+        queue.push(runnable);
+
+        promise
+    }
+
+    /// Spawns a task which output will never be retrieved.
+    ///
+    /// This is mostly useful to avoid undue reference counting for futures that
+    /// return a `()` type.
+    ///
+    /// Note that spawned tasks are not executed until [`run`](Executor::run)
+    /// is called.
+    pub(crate) fn spawn_and_forget<T>(&self, future: T)
+    where
+        T: Future + Send + 'static,
+        T::Output: Send + 'static,
+    {
+        let inner = self.inner.as_ref().unwrap();
+
+        // Book a slot to store the task cancellation token.
+        let mut active_tasks = inner.active_tasks.borrow_mut();
+        let task_entry = active_tasks.vacant_entry();
+
+        // Wrap the future so that it removes its cancel token from the
+        // executor's list when dropped.
+        let future = CancellableFuture::new(future, task_entry.key());
+
+        let (runnable, cancel_token) =
+            task::spawn_and_forget(future, schedule_task, inner.context.executor_id);
+
+        task_entry.insert(cancel_token);
+        let mut queue = inner.context.queue.borrow_mut();
+        queue.push(runnable);
+    }
+
+    /// Execute spawned tasks, blocking until all futures have completed or an
+    /// error is encountered.
+    pub(crate) fn run(&mut self, timeout: Duration) -> Result<(), ExecutorError> {
+        if timeout.is_zero() {
+            return self.inner.as_mut().unwrap().run();
+        }
+
+        // Temporarily move out the inner state so it can be moved to another
+        // thread.
+        let mut inner = self.inner.take().unwrap();
+
+        let parker = Parker::new();
+        let unparker = parker.unparker();
+        let th = thread::spawn(move || {
+            let res = inner.run();
+            unparker.unpark();
+
+            (inner, res)
+        });
+
+        if !parker.park_timeout(timeout) {
+            // Make a best-effort attempt at stopping the worker thread.
+            self.abort_signal.set();
+
+            return Err(ExecutorError::Timeout);
+        }
+
+        let (inner, res) = th.join().unwrap();
+        self.inner = Some(inner);
+
+        res
+    }
+}
+
+/// Inner state of the executor.
+struct ExecutorInner {
+    /// Shared executor data.
+    context: ExecutorContext,
+    /// List of tasks that have not completed yet.
+    active_tasks: RefCell<Slab<CancelToken>>,
+    /// Read-only handle to the simulation time.
+    simulation_context: SimulationContext,
+    /// Signal requesting the worker thread to return as soon as possible.
+    abort_signal: Signal,
+}
+
+impl ExecutorInner {
+    fn run(&mut self) -> Result<(), ExecutorError> {
+        // In case this executor is nested in another one, reset the counter of in-flight messages.
+        let msg_count_stash = channel::THREAD_MSG_COUNT.replace(self.context.msg_count);
+
+        let result = SIMULATION_CONTEXT.set(&self.simulation_context, || {
+            ACTIVE_TASKS.set(&self.active_tasks, || {
+                EXECUTOR_CONTEXT.set(&self.context, || {
+                    panic::catch_unwind(AssertUnwindSafe(|| loop {
+                        let task = match self.context.queue.borrow_mut().pop() {
+                            Some(task) => task,
+                            None => break,
+                        };
+
+                        task.run();
+
+                        if self.abort_signal.is_set() {
+                            return;
+                        }
+                    }))
+                })
+            })
+        });
+
+        // Return the panic payload, if any.
+        if let Err(payload) = result {
+            let model_id = CURRENT_MODEL_ID.take();
+
+            return Err(ExecutorError::Panic(model_id, payload));
+        }
+
+        // Check for unprocessed messages.
+        self.context.msg_count = channel::THREAD_MSG_COUNT.replace(msg_count_stash);
+        if self.context.msg_count != 0 {
+            let msg_count: usize = self.context.msg_count.try_into().unwrap();
+
+            return Err(ExecutorError::UnprocessedMessages(msg_count));
+        }
+
+        Ok(())
+    }
+}
+
+impl Drop for ExecutorInner {
+    fn drop(&mut self) {
+        // Drop all tasks that have not completed.
+        //
+        // The executor context must be set because some tasks may schedule
+        // other tasks when dropped, which requires that the work queue be
+        // available.
+        EXECUTOR_CONTEXT.set(&self.context, || {
+            // Cancel all pending futures.
+            //
+            // `ACTIVE_TASKS` is explicitly unset to prevent
+            // `CancellableFuture::drop()` from trying to remove its own token
+            // from the list of active tasks as this would result in a nested
+            // call to `borrow_mut` and thus a panic. This is mainly to stay on
+            // the safe side: `ACTIVE_TASKS` should not be set anyway, unless
+            // for some reason the executor runs inside another executor.
+            ACTIVE_TASKS.unset(|| {
+                let mut tasks = self.active_tasks.borrow_mut();
+                for task in tasks.drain() {
+                    task.cancel();
+                }
+
+                // Some of the dropped tasks may have scheduled other tasks that
+                // were not yet cancelled, preventing them from being dropped
+                // upon cancellation. This is OK: the scheduled tasks will be
+                // dropped when the work queue is dropped, and they cannot
+                // re-schedule one another since all tasks were cancelled.
+            });
+        });
+    }
+}
+
+impl fmt::Debug for Executor {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Executor").finish_non_exhaustive()
+    }
+}
+
+/// Shared executor context.
+///
+/// This contains all executor resources that can be shared between threads.
+struct ExecutorContext {
+    /// Work queue.
+    queue: RefCell<Vec<Runnable>>,
+    /// Unique executor identifier inherited by all tasks spawned on this
+    /// executor instance.
+    executor_id: usize,
+    /// Number of in-flight messages.
+    msg_count: isize,
+}
+
+impl ExecutorContext {
+    /// Creates a new shared executor context.
+    fn new(executor_id: usize) -> Self {
+        Self {
+            queue: RefCell::new(Vec::with_capacity(QUEUE_MIN_CAPACITY)),
+            executor_id,
+            msg_count: 0,
+        }
+    }
+}
+
+/// A `Future` wrapper that removes its cancellation token from the list of
+/// active tasks when dropped.
+struct CancellableFuture<T: Future> {
+    inner: T,
+    cancellation_key: usize,
+}
+
+impl<T: Future> CancellableFuture<T> {
+    /// Creates a new `CancellableFuture`.
+    fn new(fut: T, cancellation_key: usize) -> Self {
+        Self {
+            inner: fut,
+            cancellation_key,
+        }
+    }
+}
+
+impl<T: Future> Future for CancellableFuture<T> {
+    type Output = T::Output;
+
+    #[inline(always)]
+    fn poll(
+        self: std::pin::Pin<&mut Self>,
+        cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Self::Output> {
+        unsafe { self.map_unchecked_mut(|s| &mut s.inner).poll(cx) }
+    }
+}
+
+impl<T: Future> Drop for CancellableFuture<T> {
+    fn drop(&mut self) {
+        // Remove the task from the list of active tasks while the executor is
+        // running (meaning that `ACTIVE_TASK` is set). Otherwise do nothing and
+        // let the executor's drop handler do the cleanup.
+        let _ = ACTIVE_TASKS.map(|active_tasks| {
+            // Don't use `borrow_mut()` because this function can be called from
+            // a destructor and should not panic. In the worse case, the cancel
+            // token will be left in the list of active tasks, which does
+            // prevents eager task deallocation but does not cause any issue
+            // otherwise.
+            if let Ok(mut active_tasks) = active_tasks.try_borrow_mut() {
+                let _cancel_token = active_tasks.try_remove(self.cancellation_key);
+            }
+        });
+    }
+}
+
+/// Schedules a `Runnable` from within a worker thread.
+///
+/// # Panics
+///
+/// This function will panic if called from outside the executor worker thread
+/// or from another executor instance than the one the task for this `Runnable`
+/// was spawned on.
+fn schedule_task(task: Runnable, executor_id: usize) {
+    EXECUTOR_CONTEXT
+        .map(|context| {
+            // Check that this task was indeed spawned on this executor.
+            assert_eq!(
+                executor_id, context.executor_id,
+                "Tasks must be awaken on the same executor they are spawned on"
+            );
+
+            let mut queue = context.queue.borrow_mut();
+            queue.push(task);
+        })
+        .expect("Tasks may not be awaken outside executor threads");
+}

nexosim/src/executor/task.rs

@@ -125,13 +125,6 @@ where
     S: Fn(Runnable, T) + Send + Sync + 'static,
     T: Clone + Send + Sync + 'static,
 {
-    const RAW_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(
-        Self::clone_waker,
-        Self::wake_by_val,
-        Self::wake_by_ref,
-        Self::drop_waker,
-    );
-
     /// Clones a waker.
     unsafe fn clone_waker(ptr: *const ()) -> RawWaker {
         let this = &*(ptr as *const Self);
@@ -141,7 +134,7 @@ where
             panic!("Attack of the clones: the waker was cloned too many times");
         }
 
-        RawWaker::new(ptr, &Self::RAW_WAKER_VTABLE)
+        RawWaker::new(ptr, raw_waker_vtable::<F, S, T>())
     }
 
     /// Wakes the task by value.
@@ -287,11 +280,42 @@ where
     }
 }
 
+/// Returns a reference to the waker's virtual table.
+///
+/// Unfortunately, Rust will sometimes create multiple memory instances of the
+/// virtual table for the same generic parameters, which defeats
+/// `Waker::will_wake` as the latter tests the pointers to the virtual tables
+/// for equality.
+///
+/// Preventing the function from being inlined appears to solve this problem,
+/// but we may want to investigate more robust methods. For unrelated reasons,
+/// Tokio has switched [1] to a single non-generic virtual table declared as
+/// `static` which then delegates each call to another virtual call. This does
+/// ensure that `Waker::will_wake` will always work, but the double indirection
+/// is a bit unfortunate and its cost would need to be evaluated.
+///
+/// [1]: https://github.com/tokio-rs/tokio/pull/5213
+#[inline(never)]
+fn raw_waker_vtable<F, S, T>() -> &'static RawWakerVTable
+where
+    F: Future + Send + 'static,
+    F::Output: Send + 'static,
+    S: Fn(Runnable, T) + Send + Sync + 'static,
+    T: Clone + Send + Sync + 'static,
+{
+    &RawWakerVTable::new(
+        Task::<F, S, T>::clone_waker,
+        Task::<F, S, T>::wake_by_val,
+        Task::<F, S, T>::wake_by_ref,
+        Task::<F, S, T>::drop_waker,
+    )
+}
+
 /// Spawns a task.
 ///
 /// An arbitrary tag can be attached to the task, a clone of which will be
 /// passed to the scheduling function each time it is called.
-
+///
 /// The returned `Runnable` must be scheduled by the user.
 pub(crate) fn spawn<F, S, T>(
     future: F,

nexosim/src/executor/task/cancel_token.rs

@@ -25,7 +25,7 @@ struct VTable {
 /// but not currently scheduled (no `Runnable` exist) then the future is
 /// dropped immediately. Otherwise, the future will be dropped at a later
 /// time by the scheduled `Runnable` once it runs.
-unsafe fn cancel<F: Future, S, T>(ptr: *const ())
+unsafe fn cancel<F, S, T>(ptr: *const ())
 where
     F: Future + Send + 'static,
     F::Output: Send + 'static,
@@ -123,7 +123,7 @@ where
 }
 
 /// Drops the token without cancelling the task.
-unsafe fn drop<F: Future, S, T>(ptr: *const ())
+unsafe fn drop<F, S, T>(ptr: *const ())
 where
     F: Future + Send + 'static,
     F::Output: Send + 'static,
@@ -180,7 +180,7 @@ impl CancelToken {
     ///   allocator,
     /// - the reference count has been incremented to account for this new task
     ///   reference.
-    pub(super) unsafe fn new_unchecked<F: Future, S, T>(task: *const Task<F, S, T>) -> Self
+    pub(super) unsafe fn new_unchecked<F, S, T>(task: *const Task<F, S, T>) -> Self
     where
         F: Future + Send + 'static,
         F::Output: Send + 'static,

nexosim/src/executor/task/promise.rs

@@ -20,7 +20,7 @@ struct VTable<U: Send + 'static> {
 }
 
 /// Retrieves the output of the task if ready.
-unsafe fn poll<F: Future, S, T>(ptr: *const ()) -> Stage<F::Output>
+unsafe fn poll<F, S, T>(ptr: *const ()) -> Stage<F::Output>
 where
     F: Future + Send + 'static,
     F::Output: Send + 'static,
@@ -62,7 +62,7 @@ where
 }
 
 /// Drops the promise.
-unsafe fn drop<F: Future, S, T>(ptr: *const ())
+unsafe fn drop<F, S, T>(ptr: *const ())
 where
     F: Future + Send + 'static,
     F::Output: Send + 'static,

nexosim/src/executor/task/runnable.rs

@@ -11,7 +11,7 @@ use crate::loom_exports::debug_or_loom_assert;
 use crate::loom_exports::sync::atomic::{self, AtomicU64, Ordering};
 
 use super::util::RunOnDrop;
-use super::Task;
+use super::{raw_waker_vtable, Task};
 use super::{CLOSED, POLLING, REF_MASK, WAKE_MASK};
 
 /// Virtual table for a `Runnable`.
@@ -22,7 +22,7 @@ struct VTable {
 }
 
 /// Polls the inner future.
-unsafe fn run<F: Future, S, T>(ptr: *const ())
+unsafe fn run<F, S, T>(ptr: *const ())
 where
     F: Future + Send + 'static,
     F::Output: Send + 'static,
@@ -77,7 +77,7 @@ where
         }
 
         // Poll the task.
-        let raw_waker = RawWaker::new(ptr, &Task::<F, S, T>::RAW_WAKER_VTABLE);
+        let raw_waker = RawWaker::new(ptr, raw_waker_vtable::<F, S, T>());
         let waker = ManuallyDrop::new(Waker::from_raw(raw_waker));
 
         let cx = &mut Context::from_waker(&waker);

nexosim/src/executor/task/tests.rs

@@ -0,0 +1,7 @@
+use super::*;
+
+#[cfg(not(nexosim_loom))]
+mod general;
+
+#[cfg(nexosim_loom)]
+mod loom;

nexosim/src/executor/task/tests/general.rs

@@ -136,19 +136,41 @@ impl<F: Future> Drop for MonitoredFuture<F> {
     }
 }
 
+// A future that checks whether the waker cloned from the first call to `poll`
+// tests equal with `Waker::will_wake` on the second call to `poll`.
+struct WillWakeFuture {
+    waker: Arc<Mutex<Option<std::task::Waker>>>,
+}
+impl Future for WillWakeFuture {
+    type Output = bool;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let waker = &mut self.waker.lock().unwrap();
+
+        match waker.as_ref() {
+            None => {
+                **waker = Some(cx.waker().clone());
+
+                Poll::Pending
+            }
+            Some(waker) => Poll::Ready(waker.will_wake(cx.waker())),
+        }
+    }
+}
+
 #[test]
 fn task_schedule() {
     test_prelude!();
 
     let (future, future_is_alive, output_is_alive) = MonitoredFuture::new(async move { 42 });
     let (promise, runnable, _cancel_token) = spawn(future, schedule_runnable, ());
-    assert_eq!(future_is_alive.get(), true);
-    assert_eq!(output_is_alive.get(), false);
+    assert!(future_is_alive.get());
+    assert!(!output_is_alive.get());
 
     // The task should complete immediately when ran.
     runnable.run();
-    assert_eq!(future_is_alive.get(), false);
-    assert_eq!(output_is_alive.get(), true);
+    assert!(!future_is_alive.get());
+    assert!(output_is_alive.get());
     assert_eq!(promise.poll().map(|v| *v), Stage::Ready(42));
 }
 
@@ -178,13 +200,13 @@ fn task_schedule_and_forget() {
 
     let (future, future_is_alive, output_is_alive) = MonitoredFuture::new(async {});
     let (runnable, _cancel_token) = spawn_and_forget(future, schedule_runnable, ());
-    assert_eq!(future_is_alive.get(), true);
-    assert_eq!(output_is_alive.get(), false);
+    assert!(future_is_alive.get());
+    assert!(!output_is_alive.get());
 
     // The task should complete immediately when ran.
     runnable.run();
-    assert_eq!(future_is_alive.get(), false);
-    assert_eq!(output_is_alive.get(), true);
+    assert!(!future_is_alive.get());
+    assert!(output_is_alive.get());
 }
 
 #[test]
@@ -193,25 +215,23 @@ fn task_wake() {
 
     let (sender, receiver) = oneshot::channel();
 
-    let (future, future_is_alive, output_is_alive) = MonitoredFuture::new(async move {
-        let result = receiver.await.unwrap();
-        result
-    });
+    let (future, future_is_alive, output_is_alive) =
+        MonitoredFuture::new(async move { receiver.await.unwrap() });
 
     let (promise, runnable, _cancel_token) = spawn(future, schedule_runnable, ());
     runnable.run();
 
     // The future should have been polled but should not have completed.
-    assert_eq!(output_is_alive.get(), false);
+    assert!(!output_is_alive.get());
     assert!(promise.poll().is_pending());
 
     // Wake the task.
     sender.send(42).unwrap();
 
     // The task should have been scheduled by the channel sender.
-    assert_eq!(run_scheduled_runnable(), true);
-    assert_eq!(future_is_alive.get(), false);
-    assert_eq!(output_is_alive.get(), true);
+    assert!(run_scheduled_runnable());
+    assert!(!future_is_alive.get());
+    assert!(output_is_alive.get());
     assert_eq!(promise.poll().map(|v| *v), Stage::Ready(42));
 }
 
@@ -222,10 +242,7 @@ fn task_wake_mt() {
     let (sender, receiver) = oneshot::channel();
 
     let (promise, runnable, _cancel_token) = spawn(
-        async move {
-            let result = receiver.await.unwrap();
-            result
-        },
+        async move { receiver.await.unwrap() },
         schedule_runnable,
         (),
     );
@@ -262,15 +279,15 @@ fn task_wake_and_forget() {
     runnable.run();
 
     // The future should have been polled but should not have completed.
-    assert_eq!(output_is_alive.get(), false);
+    assert!(!output_is_alive.get());
 
     // Wake the task.
     sender.send(42).unwrap();
 
     // The task should have been scheduled by the channel sender.
-    assert_eq!(run_scheduled_runnable(), true);
-    assert_eq!(future_is_alive.get(), false);
-    assert_eq!(output_is_alive.get(), true);
+    assert!(run_scheduled_runnable());
+    assert!(!future_is_alive.get());
+    assert!(output_is_alive.get());
 }
 
 #[test]
@@ -299,7 +316,7 @@ fn task_multiple_wake() {
     sender.try_send(3).unwrap();
 
     // The task should have been scheduled by the channel sender.
-    assert_eq!(run_scheduled_runnable(), true);
+    assert!(run_scheduled_runnable());
     assert!(promise.poll().is_pending());
 
     // The channel should be empty. Wake the task 2 more times.
@@ -307,11 +324,11 @@ fn task_multiple_wake() {
     sender.try_send(5).unwrap();
 
     // The task should have been scheduled by the channel sender.
-    assert_eq!(run_scheduled_runnable(), true);
+    assert!(run_scheduled_runnable());
 
     // The task should have completed.
-    assert_eq!(future_is_alive.get(), false);
-    assert_eq!(output_is_alive.get(), true);
+    assert!(!future_is_alive.get());
+    assert!(output_is_alive.get());
     assert_eq!(promise.poll().map(|v| *v), Stage::Ready(15));
 }
 
@@ -379,13 +396,13 @@ fn task_cancel_scheduled() {
 
     // The future should not be dropped while the `Runnable` exists, even if the
     // task is cancelled, but the task should be seen as cancelled.
-    assert_eq!(future_is_alive.get(), true);
+    assert!(future_is_alive.get());
     assert!(promise.poll().is_cancelled());
 
     // An attempt to run the task should now drop the future without polling it.
     runnable.run();
-    assert_eq!(future_is_alive.get(), false);
-    assert_eq!(output_is_alive.get(), false);
+    assert!(!future_is_alive.get());
+    assert!(!output_is_alive.get());
 }
 
 #[test]
@@ -400,8 +417,8 @@ fn task_cancel_unscheduled() {
 
     let (promise, runnable, cancel_token) = spawn(future, schedule_runnable, ());
     runnable.run();
-    assert_eq!(future_is_alive.get(), true);
-    assert_eq!(output_is_alive.get(), false);
+    assert!(future_is_alive.get());
+    assert!(!output_is_alive.get());
 
     // Cancel the task while no `Runnable` exists (the task is not scheduled as
     // it needs to be woken by the channel sender first).
@@ -411,8 +428,8 @@ fn task_cancel_unscheduled() {
 
     // The future should be dropped immediately upon cancellation without
     // completing.
-    assert_eq!(future_is_alive.get(), false);
-    assert_eq!(output_is_alive.get(), false);
+    assert!(!future_is_alive.get());
+    assert!(!output_is_alive.get());
 }
 
 #[test]
@@ -423,12 +440,12 @@ fn task_cancel_completed() {
 
     let (promise, runnable, cancel_token) = spawn(future, schedule_runnable, ());
     runnable.run();
-    assert_eq!(future_is_alive.get(), false);
-    assert_eq!(output_is_alive.get(), true);
+    assert!(!future_is_alive.get());
+    assert!(output_is_alive.get());
 
     // Cancel the already completed task.
     cancel_token.cancel();
-    assert_eq!(output_is_alive.get(), true);
+    assert!(output_is_alive.get());
     assert_eq!(promise.poll().map(|v| *v), Stage::Ready(42));
 }
 
@@ -457,8 +474,8 @@ fn task_drop_promise_scheduled() {
 
     // The task should complete immediately when ran.
     runnable.run();
-    assert_eq!(future_is_alive.get(), false);
-    assert_eq!(output_is_alive.get(), true);
+    assert!(!future_is_alive.get());
+    assert!(output_is_alive.get());
 }
 
 #[test]
@@ -482,9 +499,9 @@ fn task_drop_promise_unscheduled() {
     assert!(sender.send(()).is_ok());
 
     // The task should have been scheduled by the channel sender.
-    assert_eq!(run_scheduled_runnable(), true);
-    assert_eq!(future_is_alive.get(), false);
-    assert_eq!(output_is_alive.get(), true);
+    assert!(run_scheduled_runnable());
+    assert!(!future_is_alive.get());
+    assert!(output_is_alive.get());
 }
 
 #[test]
@@ -516,9 +533,9 @@ fn task_drop_runnable() {
     assert!(sender.send(()).is_ok());
 
     // Drop the task scheduled by the channel sender.
-    assert_eq!(drop_runnable(), true);
-    assert_eq!(future_is_alive.get(), false);
-    assert_eq!(output_is_alive.get(), false);
+    assert!(drop_runnable());
+    assert!(!future_is_alive.get());
+    assert!(!output_is_alive.get());
     assert!(promise.poll().is_cancelled());
 }
 
@@ -623,3 +640,24 @@ fn task_drop_cycle() {
 
     assert_eq!(DROP_COUNT.load(Ordering::Relaxed), 3);
 }
+
+#[test]
+fn task_will_wake() {
+    test_prelude!();
+
+    let waker = Arc::new(Mutex::new(None));
+    let future = WillWakeFuture {
+        waker: waker.clone(),
+    };
+
+    let (promise, runnable, _cancel_token) = spawn(future, schedule_runnable, ());
+    runnable.run();
+
+    assert!(promise.poll().is_pending());
+
+    // Wake the future so it is scheduled another time.
+    waker.lock().unwrap().as_ref().unwrap().wake_by_ref();
+    assert!(run_scheduled_runnable());
+
+    assert_eq!(promise.poll(), Stage::Ready(true));
+}

nexosim/src/lib.rs

@@ -1,9 +1,9 @@
 //! A high-performance, discrete-event computation framework for system
 //! simulation.
 //!
-//! Asynchronix is a developer-friendly, yet highly optimized software simulator
-//! able to scale to very large simulation with complex time-driven state
-//! machines.
+//! NeXosim (né Asynchronix) is a developer-friendly, yet highly optimized
+//! software simulator able to scale to very large simulation with complex
+//! time-driven state machines.
 //!
 //! It promotes a component-oriented architecture that is familiar to system
 //! engineers and closely resembles [flow-based programming][FBP]: a model is
@@ -12,10 +12,10 @@
 //! defined during bench assembly. Unlike in conventional flow-based
 //! programming, request-reply patterns are also possible.
 //!
-//! Asynchronix leverages asynchronous programming to perform
-//! auto-parallelization in a manner that is fully transparent to model authors
-//! and users, achieving high computational throughput on large simulation
-//! benches by means of a custom multi-threaded executor.
+//! NeXosim leverages asynchronous programming to perform auto-parallelization
+//! in a manner that is fully transparent to model authors and users, achieving
+//! high computational throughput on large simulation benches by means of a
+//! custom multi-threaded executor.
 //!
 //!
 //! [FBP]: https://en.wikipedia.org/wiki/Flow-based_programming
@@ -36,32 +36,45 @@
 //!
 //! Models can contain four kinds of ports:
 //!
-//! * _output ports_, which are instances of the [`Output`](model::Output) type
+//! * _output ports_, which are instances of the [`Output`](ports::Output) type
 //!   and can be used to broadcast a message,
 //! * _requestor ports_, which are instances of the
-//!   [`Requestor`](model::Requestor) type and can be used to broadcast a
-//!   message and receive an iterator yielding the replies from all connected
-//!   replier ports,
+//!   [`Requestor`](ports::Requestor) or [`UniRequestor`](ports::UniRequestor)
+//!   types and can be used to broadcast a message and receive an iterator
+//!   yielding the replies from all connected replier ports,
 //! * _input ports_, which are synchronous or asynchronous methods that
-//!   implement the [`InputFn`](model::InputFn) trait and take an `&mut self`
+//!   implement the [`InputFn`](ports::InputFn) trait and take an `&mut self`
 //!   argument, a message argument, and an optional
-//!   [`&Scheduler`](time::Scheduler) argument,
+//!   [`&mut Context`](model::Context) argument,
 //! * _replier ports_, which are similar to input ports but implement the
-//!   [`ReplierFn`](model::ReplierFn) trait and return a reply.
+//!   [`ReplierFn`](ports::ReplierFn) trait and return a reply.
 //!
 //! Messages that are broadcast by an output port to an input port are referred
 //! to as *events*, while messages exchanged between requestor and replier ports
 //! are referred to as *requests* and *replies*.
 //!
 //! Models must implement the [`Model`](model::Model) trait. The main purpose of
-//! this trait is to allow models to specify an `init()` method that is
-//! guaranteed to run once and only once when the simulation is initialized,
-//! _i.e._ after all models have been connected but before the simulation
-//! starts. The `init()` method has a default implementation, so models that do
-//! not require initialization can simply implement the trait with a one-liner
-//! such as `impl Model for MyModel {}`.
+//! this trait is to allow models to specify a
+//! [`Model::init`](model::Model::init) method that is guaranteed to run once
+//! and only once when the simulation is initialized, _i.e._ after all models
+//! have been connected but before the simulation starts.
 //!
-//! #### A simple model
+//! The [`Model::init`](model::Model::init) methods has a default
+//! implementations, so models that do not require setup and initialization can
+//! simply implement the trait with a one-liner such as `impl Model for MyModel
+//! {}`.
+//!
+//! More complex models can be built with the [`ProtoModel`](model::ProtoModel)
+//! trait. The [`ProtoModel::build`](model::ProtoModel::build) method makes it
+//! possible to:
+//!
+//! * build the final [`Model`](model::Model) from a builder (the *model prototype*),
+//! * perform possibly blocking actions when the model is added to the
+//!   simulation rather than when the simulation starts, such as establishing a
+//!   network connection or configuring hardware devices,
+//! * connect submodels and add them to the simulation.
+//!
+//! ### A simple model
 //!
 //! Let us consider for illustration a simple model that forwards its input
 //! after multiplying it by 2. This model has only one input and one output
@@ -70,7 +83,7 @@
 //! ```text
 //!                ┌────────────┐
 //!                │            │
-//! Input ●───────▶│ Multiplier ├───────▶ Output
+//! Input ●───────►│ Multiplier ├───────► Output
 //!          f64   │            │  f64
 //!                └────────────┘
 //! ```
@@ -78,7 +91,8 @@
 //! `Multiplier` could be implemented as follows:
 //!
 //! ```
-//! use asynchronix::model::{Model, Output};
+//! use nexosim::model::Model;
+//! use nexosim::ports::Output;
 //!
 //! #[derive(Default)]
 //! pub struct Multiplier {
@@ -92,28 +106,28 @@
 //! impl Model for Multiplier {}
 //! ```
 //!
-//! #### A model using the local scheduler
+//! ### A model using the local context
 //!
 //! Models frequently need to schedule actions at a future time or simply get
 //! access to the current simulation time. To do so, input and replier methods
-//! can take an optional argument that gives them access to a local scheduler.
+//! can take an optional argument that gives them access to a local context.
 //!
-//! To show how the local scheduler can be used in practice, let us implement
+//! To show how the local context can be used in practice, let us implement
 //! `Delay`, a model which simply forwards its input unmodified after a 1s
 //! delay:
 //!
 //! ```
 //! use std::time::Duration;
-//! use asynchronix::model::{Model, Output};
-//! use asynchronix::time::Scheduler;
+//! use nexosim::model::{Context, Model};
+//! use nexosim::ports::Output;
 //!
 //! #[derive(Default)]
 //! pub struct Delay {
 //!    pub output: Output<f64>,
 //! }
 //! impl Delay {
-//!     pub fn input(&mut self, value: f64, scheduler: &Scheduler<Self>) {
-//!         scheduler.schedule_event(Duration::from_secs(1), Self::send, value).unwrap();
+//!     pub fn input(&mut self, value: f64, cx: &mut Context<Self>) {
+//!         cx.schedule_event(Duration::from_secs(1), Self::send, value).unwrap();
 //!     }
 //!
 //!     async fn send(&mut self, value: f64) {
@@ -135,7 +149,7 @@
 //! [`Address`](simulation::Mailbox)es pointing to that mailbox.
 //!
 //! Addresses are used among others to connect models: each output or requestor
-//! ports has a `connect()` method that takes as argument a function pointer to
+//! port has a `connect` method that takes as argument a function pointer to
 //! the corresponding input or replier port method and the address of the
 //! targeted model.
 //!
@@ -150,13 +164,13 @@
 //! ```text
 //!                                ┌────────────┐
 //!                                │            │
-//!                            ┌──▶│   Delay    ├──┐
+//!                            ┌──►│   Delay    ├──┐
 //!           ┌────────────┐   │   │            │  │   ┌────────────┐
 //!           │            │   │   └────────────┘  │   │            │
-//! Input ●──▶│ Multiplier ├───┤                   ├──▶│   Delay    ├──▶ Output
+//! Input ●──►│ Multiplier ├───┤                   ├──►│   Delay    ├──► Output
 //!           │            │   │   ┌────────────┐  │   │            │
 //!           └────────────┘   │   │            │  │   └────────────┘
-//!                            └──▶│ Multiplier ├──┘
+//!                            └──►│ Multiplier ├──┘
 //!                                │            │
 //!                                └────────────┘
 //! ```
@@ -166,8 +180,8 @@
 //! ```
 //! # mod models {
 //! #     use std::time::Duration;
-//! #     use asynchronix::model::{Model, Output};
-//! #     use asynchronix::time::Scheduler;
+//! #     use nexosim::model::{Context, Model};
+//! #     use nexosim::ports::Output;
 //! #     #[derive(Default)]
 //! #     pub struct Multiplier {
 //! #         pub output: Output<f64>,
@@ -183,8 +197,8 @@
 //! #        pub output: Output<f64>,
 //! #     }
 //! #     impl Delay {
-//! #         pub fn input(&mut self, value: f64, scheduler: &Scheduler<Self>) {
-//! #             scheduler.schedule_event(Duration::from_secs(1), Self::send, value).unwrap();
+//! #         pub fn input(&mut self, value: f64, cx: &mut Context<Self>) {
+//! #             cx.schedule_event(Duration::from_secs(1), Self::send, value).unwrap();
 //! #         }
 //! #         async fn send(&mut self, value: f64) { // this method can be private
 //! #             self.output.send(value).await;
@@ -193,8 +207,9 @@
 //! #     impl Model for Delay {}
 //! # }
 //! use std::time::Duration;
-//! use asynchronix::simulation::{Mailbox, SimInit};
-//! use asynchronix::time::MonotonicTime;
+//! use nexosim::ports::EventSlot;
+//! use nexosim::simulation::{Mailbox, SimInit};
+//! use nexosim::time::MonotonicTime;
 //!
 //! use models::{Delay, Multiplier};
 //!
@@ -217,17 +232,20 @@
 //! delay1.output.connect(Delay::input, &delay2_mbox);
 //!
 //! // Keep handles to the system input and output for the simulation.
-//! let mut output_slot = delay2.output.connect_slot().0;
+//! let mut output_slot = EventSlot::new();
+//! delay2.output.connect_sink(&output_slot);
 //! let input_address = multiplier1_mbox.address();
 //!
 //! // Pick an arbitrary simulation start time and build the simulation.
 //! let t0 = MonotonicTime::EPOCH;
-//! let mut simu = SimInit::new()
-//!     .add_model(multiplier1, multiplier1_mbox)
-//!     .add_model(multiplier2, multiplier2_mbox)
-//!     .add_model(delay1, delay1_mbox)
-//!     .add_model(delay2, delay2_mbox)
-//!     .init(t0);
+//! let (mut simu, scheduler) = SimInit::new()
+//!     .add_model(multiplier1, multiplier1_mbox, "multiplier1")
+//!     .add_model(multiplier2, multiplier2_mbox, "multiplier2")
+//!     .add_model(delay1, delay1_mbox, "delay1")
+//!     .add_model(delay2, delay2_mbox, "delay2")
+//!     .init(t0)?;
+//!
+//! # Ok::<(), nexosim::simulation::SimulationError>(())
 //! ```
 //!
 //! ## Running simulations
@@ -235,30 +253,27 @@
 //! The simulation can be controlled in several ways:
 //!
 //! 1. by advancing time, either until the next scheduled event with
-//!    [`Simulation::step()`](simulation::Simulation::step), or until a specific
-//!    deadline using for instance
-//!    [`Simulation::step_by()`](simulation::Simulation::step_by).
+//!    [`Simulation::step`](simulation::Simulation::step), until a specific
+//!    deadline with
+//!    [`Simulation::step_until`](simulation::Simulation::step_until), or
+//!    until there are no more scheduled events with
+//!    [`Simulation::step_unbounded`](simulation::Simulation::step_unbounded).
 //! 2. by sending events or queries without advancing simulation time, using
-//!    [`Simulation::send_event()`](simulation::Simulation::send_event) or
-//!    [`Simulation::send_query()`](simulation::Simulation::send_query),
-//! 3. by scheduling events, using for instance
-//!    [`Simulation::schedule_event()`](simulation::Simulation::schedule_event).
+//!    [`Simulation::process_event`](simulation::Simulation::process_event) or
+//!    [`Simulation::send_query`](simulation::Simulation::process_query),
+//! 3. by scheduling events with a [`Scheduler`](simulation::Scheduler).
 //!
-//! When a simulation is initialized via
-//! [`SimInit::init()`](simulation::SimInit::init) then the simulation will run
-//! as fast as possible, without regard for the actual wall clock time.
-//! Alternatively, it is possible to initialize a simulation via
-//! [`SimInit::init_with_clock()`](simulation::SimInit::init_with_clock) to bind
-//! the simulation time to the wall clock time using a custom
-//! [`Clock`](time::Clock) type or a readily-available real-time clock such as
-//! [`AutoSystemClock`](time::AutoSystemClock).
+//! When initialized with the default clock, the simulation will run as fast as
+//! possible, without regard for the actual wall clock time. Alternatively, the
+//! simulation time can be synchronized to the wall clock time using
+//! [`SimInit::set_clock`](simulation::SimInit::set_clock) and providing a
+//! custom [`Clock`](time::Clock) type or a readily-available real-time clock
+//! such as [`AutoSystemClock`](time::AutoSystemClock).
 //!
-//! Simulation outputs can be monitored using
-//! [`EventSlot`](simulation::EventSlot)s and
-//! [`EventStream`](simulation::EventStream)s, which can be connected to any
-//! model's output port. While an event slot only gives access to the last value
-//! sent from a port, an event stream is an iterator that yields all events that
-//! were sent in first-in-first-out order.
+//! Simulation outputs can be monitored using [`EventSlot`](ports::EventSlot)s,
+//! [`EventBuffer`](ports::EventBuffer)s, or any implementer of the
+//! [`EventSink`](ports::EventSink) trait, connected to one or several model
+//! output ports.
 //!
 //! This is an example of simulation that could be performed using the above
 //! bench assembly:
@@ -266,8 +281,8 @@
 //! ```
 //! # mod models {
 //! #     use std::time::Duration;
-//! #     use asynchronix::model::{Model, Output};
-//! #     use asynchronix::time::Scheduler;
+//! #     use nexosim::model::{Context, Model};
+//! #     use nexosim::ports::Output;
 //! #     #[derive(Default)]
 //! #     pub struct Multiplier {
 //! #         pub output: Output<f64>,
@@ -283,8 +298,8 @@
 //! #        pub output: Output<f64>,
 //! #     }
 //! #     impl Delay {
-//! #         pub fn input(&mut self, value: f64, scheduler: &Scheduler<Self>) {
-//! #             scheduler.schedule_event(Duration::from_secs(1), Self::send, value).unwrap();
+//! #         pub fn input(&mut self, value: f64, cx: &mut Context<Self>) {
+//! #             cx.schedule_event(Duration::from_secs(1), Self::send, value).unwrap();
 //! #         }
 //! #         async fn send(&mut self, value: f64) { // this method can be private
 //! #             self.output.send(value).await;
@@ -293,8 +308,9 @@
 //! #     impl Model for Delay {}
 //! # }
 //! # use std::time::Duration;
-//! # use asynchronix::simulation::{Mailbox, SimInit};
-//! # use asynchronix::time::MonotonicTime;
+//! # use nexosim::ports::EventSlot;
+//! # use nexosim::simulation::{Mailbox, SimInit};
+//! # use nexosim::time::MonotonicTime;
 //! # use models::{Delay, Multiplier};
 //! # let mut multiplier1 = Multiplier::default();
 //! # let mut multiplier2 = Multiplier::default();
@@ -308,47 +324,51 @@
 //! # multiplier1.output.connect(Multiplier::input, &multiplier2_mbox);
 //! # multiplier2.output.connect(Delay::input, &delay2_mbox);
 //! # delay1.output.connect(Delay::input, &delay2_mbox);
-//! # let mut output_slot = delay2.output.connect_slot().0;
+//! # let mut output_slot = EventSlot::new();
+//! # delay2.output.connect_sink(&output_slot);
 //! # let input_address = multiplier1_mbox.address();
 //! # let t0 = MonotonicTime::EPOCH;
 //! # let mut simu = SimInit::new()
-//! #     .add_model(multiplier1, multiplier1_mbox)
-//! #     .add_model(multiplier2, multiplier2_mbox)
-//! #     .add_model(delay1, delay1_mbox)
-//! #     .add_model(delay2, delay2_mbox)
-//! #     .init(t0);
+//! #     .add_model(multiplier1, multiplier1_mbox, "multiplier1")
+//! #     .add_model(multiplier2, multiplier2_mbox, "multiplier2")
+//! #     .add_model(delay1, delay1_mbox, "delay1")
+//! #     .add_model(delay2, delay2_mbox, "delay2")
+//! #     .init(t0)?
+//! #     .0;
 //! // Send a value to the first multiplier.
-//! simu.send_event(Multiplier::input, 21.0, &input_address);
+//! simu.process_event(Multiplier::input, 21.0, &input_address)?;
 //!
 //! // The simulation is still at t0 so nothing is expected at the output of the
 //! // second delay gate.
-//! assert!(output_slot.take().is_none());
+//! assert!(output_slot.next().is_none());
 //!
 //! // Advance simulation time until the next event and check the time and output.
-//! simu.step();
+//! simu.step()?;
 //! assert_eq!(simu.time(), t0 + Duration::from_secs(1));
-//! assert_eq!(output_slot.take(), Some(84.0));
+//! assert_eq!(output_slot.next(), Some(84.0));
 //!
 //! // Get the answer to the ultimate question of life, the universe & everything.
-//! simu.step();
+//! simu.step()?;
 //! assert_eq!(simu.time(), t0 + Duration::from_secs(2));
-//! assert_eq!(output_slot.take(), Some(42.0));
+//! assert_eq!(output_slot.next(), Some(42.0));
+//!
+//! # Ok::<(), nexosim::simulation::SimulationError>(())
 //! ```
 //!
 //! # Message ordering guarantees
 //!
-//! The Asynchronix runtime is based on the [actor model][actor_model], meaning
-//! that every simulation model can be thought of as an isolated entity running
-//! in its own thread. While in practice the runtime will actually multiplex and
+//! The NeXosim runtime is based on the [actor model][actor_model], meaning that
+//! every simulation model can be thought of as an isolated entity running in
+//! its own thread. While in practice the runtime will actually multiplex and
 //! migrate models over a fixed set of kernel threads, models will indeed run in
 //! parallel whenever possible.
 //!
-//! Since Asynchronix is a time-based simulator, the runtime will always execute
+//! Since NeXosim is a time-based simulator, the runtime will always execute
 //! tasks in chronological order, thus eliminating most ordering ambiguities
 //! that could result from parallel execution. Nevertheless, it is sometimes
 //! possible for events and queries generated in the same time slice to lead to
 //! ambiguous execution orders. In order to make it easier to reason about such
-//! situations, Asynchronix provides a set of guarantees about message delivery
+//! situations, NeXosim provides a set of guarantees about message delivery
 //! order. Borrowing from the [Pony][pony] programming language, we refer to
 //! this contract as *causal messaging*, a property that can be summarized by
 //! these two rules:
@@ -361,54 +381,108 @@
 //!    processed in any order by `B` and `C`, it is guaranteed that `B` will
 //!    process `M1` before `M3`.
 //!
-//! The first guarantee (and only the first) also extends to events scheduled
-//! from a simulation with a
-//! [`Simulation::schedule_*()`](simulation::Simulation::schedule_event) method:
-//! if the scheduler contains several events to be delivered at the same time to
-//! the same model, these events will always be processed in the order in which
-//! they were scheduled.
+//! Both guarantees also extend to same-time events scheduled from the global
+//! [`Scheduler`](simulation::Scheduler), *i.e.* the relative ordering of events
+//! scheduled for the same time is preserved and warranties 1 and 2 above
+//! accordingly hold (assuming model `A` stands for the scheduler). Likewise,
+//! the relative order of same-time events self-scheduled by a model using its
+//! [`Context`](model::Context) is preserved.
 //!
 //! [actor_model]: https://en.wikipedia.org/wiki/Actor_model
 //! [pony]: https://www.ponylang.io/
 //!
 //!
+//! # Cargo feature flags
+//!
+//! ## Tracing
+//!
+//! The `tracing` feature flag provides support for the
+//! [`tracing`](https://docs.rs/tracing/latest/tracing/) crate and can be
+//! activated in `Cargo.toml` with:
+//!
+//! ```toml
+//! [dependencies]
+//! nexosim = { version = "0.3.1", features = ["tracing"] }
+//! ```
+//!
+//! See the [`tracing`] module for more information.
+//!
+//! ## Server
+//!
+//! The `server` feature provides a gRPC server for remote control and monitoring,
+//! e.g. from a Python client. It can be activated with:
+//!
+//! ```toml
+//! [dependencies]
+//! nexosim = { version = "0.3.1", features = ["server"] }
+//! ```
+//!
+//! See the [`registry`] and [`server`] modules for more information.
+//!
+//! Front-end usage documentation will be added upon release of the NeXosim
+//! Python client.
+//!
+//!
 //! # Other resources
 //!
 //! ## Other examples
 //!
-//! The [`examples`][gh_examples] directory in the main repository contains more
-//! fleshed out examples that demonstrate various capabilities of the simulation
+//! Several [`examples`][gh_examples] are available that contain more fleshed
+//! out examples and demonstrate various capabilities of the simulation
 //! framework.
 //!
 //! [gh_examples]:
-//!     https://github.com/asynchronics/asynchronix/tree/main/asynchronix/examples
+//!     https://github.com/asynchronics/nexosim/tree/main/nexosim/examples
 //!
-//! ## Modules documentation
 //!
-//! While the above overview does cover the basic concepts, more information is
-//! available in the documentation of the different modules:
+//! ## Other features and advanced topics
+//!
+//! While the above overview does cover most basic concepts, more information is
+//! available in the modules' documentation:
+//!
+//! * the [`model`] module provides more details about models, **model
+//!   prototypes** and **hierarchical models**; be sure to check as well the
+//!   documentation of [`model::Context`] for topics such as **self-scheduling**
+//!   methods and **event cancellation**,
+//! * the [`ports`] module discusses in more details model ports and simulation
+//!   endpoints, as well as the ability to **modify and filter messages**
+//!   exchanged between ports; it also provides
+//!   [`EventSource`](ports::EventSource) and
+//!   [`QuerySource`](ports::QuerySource) objects which can be connected to
+//!   models just like [`Output`](ports::Output) and
+//!   [`Requestor`](ports::Requestor) ports, but for use as simulation
+//!   endpoints.
+//! * the [`registry`] and [`server`] modules make it possible to manage and
+//!   monitor a simulation locally or remotely from a NeXosim Python client,
+//! * the [`simulation`] module discusses **mailbox capacity** and pathological
+//!   situations that may lead to a **deadlock**,
+//! * the [`time`] module introduces the [`time::MonotonicTime`] monotonic
+//!   timestamp object and **simulation clocks**.
+//! * the [`tracing`] module discusses time-stamping and filtering of `tracing`
+//!   events.
 //!
-//! * the [`model`] module provides more details about the signatures of input
-//!   and replier port methods and discusses model initialization in the
-//!   documentation of [`model::Model`],
-//! * the [`simulation`] module discusses how the capacity of mailboxes may
-//!   affect the simulation, how connections can be modified after the
-//!   simulation was instantiated, and which pathological situations can lead to
-//!   a deadlock,
-//! * the [`time`] module discusses in particular self-scheduling methods and
-//!   scheduling cancellation in the documentation of [`time::Scheduler`] while
-//!   the monotonic timestamp format used for simulations is documented in
-//!   [`time::MonotonicTime`].
 #![warn(missing_docs, missing_debug_implementations, unreachable_pub)]
+#![cfg_attr(docsrs, feature(doc_auto_cfg, doc_cfg_hide))]
+#![cfg_attr(docsrs, doc(cfg_hide(feature = "dev-hooks")))]
 
 pub(crate) mod channel;
 pub(crate) mod executor;
 mod loom_exports;
 pub(crate) mod macros;
 pub mod model;
+pub mod ports;
 pub mod simulation;
 pub mod time;
 pub(crate) mod util;
 
+#[cfg(feature = "server")]
+pub mod registry;
+#[cfg(feature = "server")]
+pub mod server;
+
+#[cfg(feature = "tracing")]
+pub mod tracing;
+
 #[cfg(feature = "dev-hooks")]
+#[doc(hidden)]
 pub mod dev_hooks;

nexosim/src/loom_exports.rs

@@ -1,7 +1,8 @@
-#[cfg(asynchronix_loom)]
+#[cfg(all(test, nexosim_loom))]
 #[allow(unused_imports)]
 pub(crate) mod sync {
-    pub(crate) use loom::sync::{Arc, Mutex};
+    pub(crate) use loom::sync::{Arc, LockResult, Mutex, MutexGuard};
+    pub(crate) use std::sync::PoisonError;
 
     pub(crate) mod atomic {
         pub(crate) use loom::sync::atomic::{
@@ -9,10 +10,10 @@ pub(crate) mod sync {
         };
     }
 }
-#[cfg(not(asynchronix_loom))]
+#[cfg(not(all(test, nexosim_loom)))]
 #[allow(unused_imports)]
 pub(crate) mod sync {
-    pub(crate) use std::sync::{Arc, Mutex};
+    pub(crate) use std::sync::{Arc, LockResult, Mutex, MutexGuard, PoisonError};
 
     pub(crate) mod atomic {
         pub(crate) use std::sync::atomic::{
@@ -21,11 +22,11 @@ pub(crate) mod sync {
     }
 }
 
-#[cfg(asynchronix_loom)]
+#[cfg(all(test, nexosim_loom))]
 pub(crate) mod cell {
     pub(crate) use loom::cell::UnsafeCell;
 }
-#[cfg(not(asynchronix_loom))]
+#[cfg(not(all(test, nexosim_loom)))]
 pub(crate) mod cell {
     #[derive(Debug)]
     pub(crate) struct UnsafeCell<T>(std::cell::UnsafeCell<T>);
@@ -49,11 +50,11 @@ pub(crate) mod cell {
 
 #[allow(unused_macros)]
 macro_rules! debug_or_loom_assert {
-    ($($arg:tt)*) => (if cfg!(any(debug_assertions, asynchronix_loom)) { assert!($($arg)*); })
+    ($($arg:tt)*) => (if cfg!(any(debug_assertions, nexosim_loom)) { assert!($($arg)*); })
 }
 #[allow(unused_macros)]
 macro_rules! debug_or_loom_assert_eq {
-    ($($arg:tt)*) => (if cfg!(any(debug_assertions, asynchronix_loom)) { assert_eq!($($arg)*); })
+    ($($arg:tt)*) => (if cfg!(any(debug_assertions, nexosim_loom)) { assert_eq!($($arg)*); })
 }
 #[allow(unused_imports)]
 pub(crate) use debug_or_loom_assert;

nexosim/src/macros/scoped_thread_local.rs

@@ -7,19 +7,18 @@ use std::ptr;
 /// Declare a new thread-local storage scoped key of type `ScopedKey<T>`.
 ///
 /// This is based on the `scoped-tls` crate, with slight modifications, such as
-/// the use of the newly available `const` qualifier for TLS.
+/// the addition of a `ScopedLocalKey::unset` method and the use of a `map`
+/// method that returns `Option::None` when the value is not set, rather than
+/// panicking as `with` would.
 macro_rules! scoped_thread_local {
     ($(#[$attrs:meta])* $vis:vis static $name:ident: $ty:ty) => (
         $(#[$attrs])*
         $vis static $name: $crate::macros::scoped_thread_local::ScopedLocalKey<$ty>
-            = $crate::macros::scoped_thread_local::ScopedLocalKey {
-                inner: {
-                    thread_local!(static FOO: ::std::cell::Cell<*const ()> = const {
-                        std::cell::Cell::new(::std::ptr::null())
-                    });
-                    &FOO
-                },
-                _marker: ::std::marker::PhantomData,
+            = unsafe {
+                ::std::thread_local!(static FOO: ::std::cell::Cell<*const ()> = const {
+                        ::std::cell::Cell::new(::std::ptr::null())
+                });
+                $crate::macros::scoped_thread_local::ScopedLocalKey::new(&FOO)
             };
     )
 }
@@ -28,13 +27,24 @@ pub(crate) use scoped_thread_local;
 /// Type representing a thread local storage key corresponding to a reference
 /// to the type parameter `T`.
 pub(crate) struct ScopedLocalKey<T> {
-    pub(crate) inner: &'static LocalKey<Cell<*const ()>>,
-    pub(crate) _marker: marker::PhantomData<T>,
+    inner: &'static LocalKey<Cell<*const ()>>,
+    _marker: marker::PhantomData<T>,
 }
 
 unsafe impl<T> Sync for ScopedLocalKey<T> {}
 
 impl<T> ScopedLocalKey<T> {
+    #[doc(hidden)]
+    /// # Safety
+    ///
+    /// Should only be called through the public macro.
+    pub(crate) const unsafe fn new(inner: &'static LocalKey<Cell<*const ()>>) -> Self {
+        Self {
+            inner,
+            _marker: marker::PhantomData,
+        }
+    }
+
     /// Inserts a value into this scoped thread local storage slot for the
     /// duration of a closure.
     pub(crate) fn set<F, R>(&'static self, t: &T, f: F) -> R
@@ -113,7 +123,7 @@ impl<T> ScopedLocalKey<T> {
     }
 }
 
-#[cfg(all(test, not(asynchronix_loom)))]
+#[cfg(all(test, not(nexosim_loom)))]
 mod tests {
     use std::cell::Cell;
     use std::sync::mpsc::{channel, Sender};

nexosim/src/model.rs

@@ -0,0 +1,296 @@
+//! Model components.
+//!
+//! # Models and model prototypes
+//!
+//! Every model must implement the [`Model`] trait. This trait defines an
+//! asynchronous initialization method, [`Model::init`], which main purpose is
+//! to enable models to perform specific actions when the simulation starts,
+//! *i.e.* after all models have been connected and added to the simulation.
+//!
+//! It is frequently convenient to expose to users a model builder type—called a
+//! *model prototype*—rather than the final model. This can be done by
+//! implementing the [`ProtoModel`] trait, which defines the associated model
+//! type and a [`ProtoModel::build`] method invoked when a model is added the
+//! simulation.
+//!
+//! Prototype models can be used whenever the Rust builder pattern is helpful,
+//! for instance to set optional parameters. One of the use-cases that may
+//! benefit from the use of prototype models is hierarchical model building.
+//! When a parent model contains submodels, these submodels are often an
+//! implementation detail that needs not be exposed to the user. One may then
+//! define a prototype model that contains all outputs and requestors ports,
+//! while the model itself contains the input and replier ports. Upon invocation
+//! of [`ProtoModel::build`], the exit ports are moved to the model or its
+//! submodels, and those submodels are added to the simulation.
+//!
+//! Note that a trivial [`ProtoModel`] implementation is generated by default
+//! for any object implementing the [`Model`] trait, where the associated
+//! [`ProtoModel::Model`] type is the model type itself. This is what makes it
+//! possible to use either an explicitly-defined [`ProtoModel`] as argument to
+//! the [`SimInit::add_model`](crate::simulation::SimInit::add_model) method, or
+//! a plain [`Model`] type.
+//!
+//! #### Examples
+//!
+//! A model that does not require initialization or building can simply use the
+//! default implementation of the [`Model`] trait:
+//!
+//! ```
+//! use nexosim::model::Model;
+//!
+//! pub struct MyModel {
+//!     // ...
+//! }
+//! impl Model for MyModel {}
+//! ```
+//!
+//! If a default action is required during simulation initialization, the `init`
+//! methods can be explicitly implemented:
+//!
+//! ```
+//! use nexosim::model::{Context, InitializedModel, Model};
+//!
+//! pub struct MyModel {
+//!     // ...
+//! }
+//! impl Model for MyModel {
+//!     async fn init(
+//!         mut self,
+//!         ctx: &mut Context<Self>
+//!     ) -> InitializedModel<Self> {
+//!         println!("...initialization...");
+//!
+//!         self.into()
+//!     }
+//! }
+//! ```
+//!
+//! Finally, if a model builder is required, the [`ProtoModel`] trait can be
+//! explicitly implemented. Note that the [`ProtoModel`] contains all output and
+//! requestor ports, while the associated [`Model`] contains all input and
+//! replier methods.
+//!
+//! ```
+//! use nexosim::model::{BuildContext, InitializedModel, Model, ProtoModel};
+//! use nexosim::ports::Output;
+//!
+//! /// The final model.
+//! pub struct Multiplier {
+//!     // Private outputs and requestors stored in a form that constitutes an
+//!     // implementation detail and should not be exposed to the user.
+//!     my_outputs: Vec<Output<usize>>
+//! }
+//! impl Multiplier {
+//!     // Private constructor: the final model is built by the prototype model.
+//!     fn new(
+//!         value_times_1: Output<usize>,
+//!         value_times_2: Output<usize>,
+//!         value_times_3: Output<usize>,
+//!     ) -> Self {
+//!         Self {
+//!             my_outputs: vec![value_times_1, value_times_2, value_times_3]
+//!         }
+//!     }
+//!
+//!     // Public input to be used during bench construction.
+//!     pub async fn my_input(&mut self, my_data: usize) {
+//!         for (i, output) in self.my_outputs.iter_mut().enumerate() {
+//!             output.send(my_data*(i + 1)).await;
+//!         }
+//!     }
+//! }
+//! impl Model for Multiplier {}
+//!
+//! pub struct ProtoMultiplier {
+//!     // Prettyfied outputs exposed to the user.
+//!     pub value_times_1: Output<usize>,
+//!     pub value_times_2: Output<usize>,
+//!     pub value_times_3: Output<usize>,
+//! }
+//! impl ProtoModel for ProtoMultiplier {
+//!     type Model = Multiplier;
+//!
+//!     fn build(
+//!         mut self,
+//!         _: &mut BuildContext<Self>
+//!     ) -> Multiplier {
+//!         Multiplier::new(self.value_times_1, self.value_times_2, self.value_times_3)
+//!     }
+//! }
+//! ```
+//!
+//! # Hierarchical models
+//!
+//! Hierarchical models are models build from a prototype, which prototype adds
+//! submodels to the simulation within its [`ProtoModel::build`] method. From a
+//! formal point of view, however, hierarchical models are just regular models
+//! implementing the [`Model`] trait, as are their submodels.
+//!
+//!
+//! #### Example
+//!
+//! This example demonstrates a child model inside a parent model, where the
+//! parent model simply forwards input data to the child and the child in turn
+//! sends the data to the output exposed by the parent's prototype.
+//!
+//! For a more comprehensive example demonstrating hierarchical model
+//! assemblies, see the [`assembly`][assembly] example.
+//!
+//! [assembly]:
+//!     https://github.com/asynchronics/nexosim/tree/main/nexosim/examples/assembly.rs
+//!
+//! ```
+//! use nexosim::model::{BuildContext, Model, ProtoModel};
+//! use nexosim::ports::Output;
+//! use nexosim::simulation::Mailbox;
+//!
+//! pub struct ParentModel {
+//!     // Private internal port connected to the submodel.
+//!     to_child: Output<u64>,
+//! }
+//! impl ParentModel {
+//!     async fn input(&mut self, my_data: u64) {
+//!         // Forward to the submodel.
+//!         self.to_child.send(my_data).await;
+//!     }
+//! }
+//! impl Model for ParentModel {}
+//!
+//! pub struct ProtoParentModel {
+//!     pub output: Output<u64>,
+//! }
+//! impl ProtoModel for ProtoParentModel {
+//!     type Model = ParentModel;
+//!
+//!     fn build(self, cx: &mut BuildContext<Self>) -> ParentModel {
+//!         // Move the output to the child model.
+//!         let child = ChildModel { output: self.output };
+//!         let mut parent = ParentModel {
+//!             to_child: Output::default(),
+//!         };
+//!
+//!         let child_mailbox = Mailbox::new();
+//!
+//!         // Establish an internal Parent -> Child connection.
+//!         parent
+//!             .to_child
+//!             .connect(ChildModel::input, child_mailbox.address());
+//!
+//!         // Add the child model to the simulation.
+//!         cx.add_submodel(child, child_mailbox, "child");
+//!
+//!         parent
+//!     }
+//! }
+//!
+//! struct ChildModel {
+//!     output: Output<u64>,
+//! }
+//! impl ChildModel {
+//!     async fn input(&mut self, my_data: u64) {
+//!         self.output.send(my_data).await;
+//!     }
+//! }
+//! impl Model for ChildModel {}
+//!
+//! ```
+use std::future::Future;
+
+pub use context::{BuildContext, Context};
+
+mod context;
+
+/// Trait to be implemented by simulation models.
+///
+/// This trait enables models to perform specific actions during initialization.
+/// The [`Model::init`] method is run only once all models have been connected
+/// and migrated to the simulation bench, but before the simulation actually
+/// starts. A common use for `init` is to send messages to connected models at
+/// the beginning of the simulation.
+///
+/// The `init` function converts the model to the opaque `InitializedModel` type
+/// to prevent an already initialized model from being added to the simulation
+/// bench.
+pub trait Model: Sized + Send + 'static {
+    /// Performs asynchronous model initialization.
+    ///
+    /// This asynchronous method is executed exactly once for all models of the
+    /// simulation when the
+    /// [`SimInit::init`](crate::simulation::SimInit::init) method is called.
+    ///
+    /// The default implementation simply converts the model to an
+    /// `InitializedModel` without any side effect.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::future::Future;
+    /// use std::pin::Pin;
+    ///
+    /// use nexosim::model::{Context, InitializedModel, Model};
+    ///
+    /// pub struct MyModel {
+    ///     // ...
+    /// }
+    ///
+    /// impl Model for MyModel {
+    ///     async fn init(
+    ///         self,
+    ///         cx: &mut Context<Self>
+    ///     ) -> InitializedModel<Self> {
+    ///         println!("...initialization...");
+    ///
+    ///         self.into()
+    ///     }
+    /// }
+    /// ```
+    fn init(self, _: &mut Context<Self>) -> impl Future<Output = InitializedModel<Self>> + Send {
+        async { self.into() }
+    }
+}
+
+/// Opaque type containing an initialized model.
+///
+/// A model can be converted to an `InitializedModel` using the `Into`/`From`
+/// traits. The implementation of the simulation guarantees that the
+/// [`Model::init`] method will never be called on a model after conversion to
+/// an `InitializedModel`.
+#[derive(Debug)]
+pub struct InitializedModel<M: Model>(pub(crate) M);
+
+impl<M: Model> From<M> for InitializedModel<M> {
+    fn from(model: M) -> Self {
+        InitializedModel(model)
+    }
+}
+
+/// Trait to be implemented by simulation model prototypes.
+///
+/// This trait makes it possible to build the final model from a builder type
+/// when it is added to the simulation.
+///
+/// The [`ProtoModel::build`] method consumes the prototype. It is
+/// automatically called when a model or submodel prototype is added to the
+/// simulation using
+/// [`Simulation::add_model`](crate::simulation::SimInit::add_model) or
+/// [`BuildContext::add_submodel`].
+pub trait ProtoModel: Sized {
+    /// Type of the model to be built.
+    type Model: Model;
+
+    /// Builds the model.
+    ///
+    /// This method is invoked when the
+    /// [`SimInit::add_model`](crate::simulation::SimInit::add_model) or
+    /// [`BuildContext::add_submodel`] method are called.
+    fn build(self, cx: &mut BuildContext<Self>) -> Self::Model;
+}
+
+// Every model can be used as a prototype for itself.
+impl<M: Model> ProtoModel for M {
+    type Model = Self;
+
+    fn build(self, _: &mut BuildContext<Self>) -> Self::Model {
+        self
+    }
+}

nexosim/src/model/context.rs

@@ -0,0 +1,539 @@
+use std::fmt;
+use std::time::Duration;
+
+use crate::executor::{Executor, Signal};
+use crate::ports::InputFn;
+use crate::simulation::{self, ActionKey, Address, GlobalScheduler, Mailbox, SchedulingError};
+use crate::time::{Deadline, MonotonicTime};
+
+use super::{Model, ProtoModel};
+
+#[cfg(all(test, not(nexosim_loom)))]
+use crate::channel::Receiver;
+
+/// A local context for models.
+///
+/// A `Context` is a handle to the global context associated to a model
+/// instance. It can be used by the model to retrieve the simulation time or
+/// schedule delayed actions on itself.
+///
+/// ### Caveat: self-scheduling `async` methods
+///
+/// Due to a current rustc issue, `async` methods that schedule themselves will
+/// not compile unless an explicit `Send` bound is added to the returned future.
+/// This can be done by replacing the `async` signature with a partially
+/// desugared signature such as:
+///
+/// ```ignore
+/// fn self_scheduling_method<'a>(
+///     &'a mut self,
+///     arg: MyEventType,
+///     cx: &'a mut Context<Self>
+/// ) -> impl Future<Output=()> + Send + 'a {
+///     async move {
+///         /* implementation */
+///     }
+/// }
+/// ```
+///
+/// Self-scheduling methods which are not `async` are not affected by this
+/// issue.
+///
+/// # Examples
+///
+/// A model that sends a greeting after some delay.
+///
+/// ```
+/// use std::time::Duration;
+/// use nexosim::model::{Context, Model};
+/// use nexosim::ports::Output;
+///
+/// #[derive(Default)]
+/// pub struct DelayedGreeter {
+///     msg_out: Output<String>,
+/// }
+///
+/// impl DelayedGreeter {
+///     // Triggers a greeting on the output port after some delay [input port].
+///     pub async fn greet_with_delay(&mut self, delay: Duration, cx: &mut Context<Self>) {
+///         let time = cx.time();
+///         let greeting = format!("Hello, this message was scheduled at: {:?}.", time);
+///
+///         if delay.is_zero() {
+///             self.msg_out.send(greeting).await;
+///         } else {
+///             cx.schedule_event(delay, Self::send_msg, greeting).unwrap();
+///         }
+///     }
+///
+///     // Sends a message to the output [private input port].
+///     async fn send_msg(&mut self, msg: String) {
+///         self.msg_out.send(msg).await;
+///     }
+/// }
+/// impl Model for DelayedGreeter {}
+/// ```
+// The self-scheduling caveat seems related to this issue:
+// https://github.com/rust-lang/rust/issues/78649
+pub struct Context<M: Model> {
+    name: String,
+    scheduler: GlobalScheduler,
+    address: Address<M>,
+    origin_id: usize,
+}
+
+impl<M: Model> Context<M> {
+    /// Creates a new local context.
+    pub(crate) fn new(name: String, scheduler: GlobalScheduler, address: Address<M>) -> Self {
+        // The only requirement for the origin ID is that it must be (i)
+        // specific to each model and (ii) different from 0 (which is reserved
+        // for the global scheduler). The channel ID of the model mailbox
+        // fulfills this requirement.
+        let origin_id = address.0.channel_id();
+
+        Self {
+            name,
+            scheduler,
+            address,
+            origin_id,
+        }
+    }
+
+    /// Returns the fully qualified model instance name.
+    ///
+    /// The fully qualified name is made of the unqualified model name, if
+    /// relevant prepended by the dot-separated names of all parent models.
+    pub fn name(&self) -> &str {
+        &self.name
+    }
+
+    /// Returns the current simulation time.
+    pub fn time(&self) -> MonotonicTime {
+        self.scheduler.time()
+    }
+
+    /// Schedules an event at a future time on this model.
+    ///
+    /// An error is returned if the specified deadline is not in the future of
+    /// the current simulation time.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::time::Duration;
+    ///
+    /// use nexosim::model::{Context, Model};
+    ///
+    /// // A timer.
+    /// pub struct Timer {}
+    ///
+    /// impl Timer {
+    ///     // Sets an alarm [input port].
+    ///     pub fn set(&mut self, setting: Duration, cx: &mut Context<Self>) {
+    ///         if cx.schedule_event(setting, Self::ring, ()).is_err() {
+    ///             println!("The alarm clock can only be set for a future time");
+    ///         }
+    ///     }
+    ///
+    ///     // Rings [private input port].
+    ///     fn ring(&mut self) {
+    ///         println!("Brringggg");
+    ///     }
+    /// }
+    ///
+    /// impl Model for Timer {}
+    /// ```
+    pub fn schedule_event<F, T, S>(
+        &self,
+        deadline: impl Deadline,
+        func: F,
+        arg: T,
+    ) -> Result<(), SchedulingError>
+    where
+        F: for<'a> InputFn<'a, M, T, S>,
+        T: Send + Clone + 'static,
+        S: Send + 'static,
+    {
+        self.scheduler
+            .schedule_event_from(deadline, func, arg, &self.address, self.origin_id)
+    }
+
+    /// Schedules a cancellable event at a future time on this model and returns
+    /// an action key.
+    ///
+    /// An error is returned if the specified deadline is not in the future of
+    /// the current simulation time.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use nexosim::model::{Context, Model};
+    /// use nexosim::simulation::ActionKey;
+    /// use nexosim::time::MonotonicTime;
+    ///
+    /// // An alarm clock that can be cancelled.
+    /// #[derive(Default)]
+    /// pub struct CancellableAlarmClock {
+    ///     event_key: Option<ActionKey>,
+    /// }
+    ///
+    /// impl CancellableAlarmClock {
+    ///     // Sets an alarm [input port].
+    ///     pub fn set(&mut self, setting: MonotonicTime, cx: &mut Context<Self>) {
+    ///         self.cancel();
+    ///         match cx.schedule_keyed_event(setting, Self::ring, ()) {
+    ///             Ok(event_key) => self.event_key = Some(event_key),
+    ///             Err(_) => println!("The alarm clock can only be set for a future time"),
+    ///         };
+    ///     }
+    ///
+    ///     // Cancels the current alarm, if any [input port].
+    ///     pub fn cancel(&mut self) {
+    ///         self.event_key.take().map(|k| k.cancel());
+    ///     }
+    ///
+    ///     // Rings the alarm [private input port].
+    ///     fn ring(&mut self) {
+    ///         println!("Brringggg!");
+    ///     }
+    /// }
+    ///
+    /// impl Model for CancellableAlarmClock {}
+    /// ```
+    pub fn schedule_keyed_event<F, T, S>(
+        &self,
+        deadline: impl Deadline,
+        func: F,
+        arg: T,
+    ) -> Result<ActionKey, SchedulingError>
+    where
+        F: for<'a> InputFn<'a, M, T, S>,
+        T: Send + Clone + 'static,
+        S: Send + 'static,
+    {
+        let event_key = self.scheduler.schedule_keyed_event_from(
+            deadline,
+            func,
+            arg,
+            &self.address,
+            self.origin_id,
+        )?;
+
+        Ok(event_key)
+    }
+
+    /// Schedules a periodically recurring event on this model at a future time.
+    ///
+    /// An error is returned if the specified deadline is not in the future of
+    /// the current simulation time or if the specified period is null.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::time::Duration;
+    ///
+    /// use nexosim::model::{Context, Model};
+    /// use nexosim::time::MonotonicTime;
+    ///
+    /// // An alarm clock beeping at 1Hz.
+    /// pub struct BeepingAlarmClock {}
+    ///
+    /// impl BeepingAlarmClock {
+    ///     // Sets an alarm [input port].
+    ///     pub fn set(&mut self, setting: MonotonicTime, cx: &mut Context<Self>) {
+    ///         if cx.schedule_periodic_event(
+    ///             setting,
+    ///             Duration::from_secs(1), // 1Hz = 1/1s
+    ///             Self::beep,
+    ///             ()
+    ///         ).is_err() {
+    ///             println!("The alarm clock can only be set for a future time");
+    ///         }
+    ///     }
+    ///
+    ///     // Emits a single beep [private input port].
+    ///     fn beep(&mut self) {
+    ///         println!("Beep!");
+    ///     }
+    /// }
+    ///
+    /// impl Model for BeepingAlarmClock {}
+    /// ```
+    pub fn schedule_periodic_event<F, T, S>(
+        &self,
+        deadline: impl Deadline,
+        period: Duration,
+        func: F,
+        arg: T,
+    ) -> Result<(), SchedulingError>
+    where
+        F: for<'a> InputFn<'a, M, T, S> + Clone,
+        T: Send + Clone + 'static,
+        S: Send + 'static,
+    {
+        self.scheduler.schedule_periodic_event_from(
+            deadline,
+            period,
+            func,
+            arg,
+            &self.address,
+            self.origin_id,
+        )
+    }
+
+    /// Schedules a cancellable, periodically recurring event on this model at a
+    /// future time and returns an action key.
+    ///
+    /// An error is returned if the specified deadline is not in the future of
+    /// the current simulation time or if the specified period is null.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::time::Duration;
+    ///
+    /// use nexosim::model::{Context, Model};
+    /// use nexosim::simulation::ActionKey;
+    /// use nexosim::time::MonotonicTime;
+    ///
+    /// // An alarm clock beeping at 1Hz that can be cancelled before it sets off, or
+    /// // stopped after it sets off.
+    /// #[derive(Default)]
+    /// pub struct CancellableBeepingAlarmClock {
+    ///     event_key: Option<ActionKey>,
+    /// }
+    ///
+    /// impl CancellableBeepingAlarmClock {
+    ///     // Sets an alarm [input port].
+    ///     pub fn set(&mut self, setting: MonotonicTime, cx: &mut Context<Self>) {
+    ///         self.cancel();
+    ///         match cx.schedule_keyed_periodic_event(
+    ///             setting,
+    ///             Duration::from_secs(1), // 1Hz = 1/1s
+    ///             Self::beep,
+    ///             ()
+    ///         ) {
+    ///             Ok(event_key) => self.event_key = Some(event_key),
+    ///             Err(_) => println!("The alarm clock can only be set for a future time"),
+    ///         };
+    ///     }
+    ///
+    ///     // Cancels or stops the alarm [input port].
+    ///     pub fn cancel(&mut self) {
+    ///         self.event_key.take().map(|k| k.cancel());
+    ///     }
+    ///
+    ///     // Emits a single beep [private input port].
+    ///     fn beep(&mut self) {
+    ///         println!("Beep!");
+    ///     }
+    /// }
+    ///
+    /// impl Model for CancellableBeepingAlarmClock {}
+    /// ```
+    pub fn schedule_keyed_periodic_event<F, T, S>(
+        &self,
+        deadline: impl Deadline,
+        period: Duration,
+        func: F,
+        arg: T,
+    ) -> Result<ActionKey, SchedulingError>
+    where
+        F: for<'a> InputFn<'a, M, T, S> + Clone,
+        T: Send + Clone + 'static,
+        S: Send + 'static,
+    {
+        let event_key = self.scheduler.schedule_keyed_periodic_event_from(
+            deadline,
+            period,
+            func,
+            arg,
+            &self.address,
+            self.origin_id,
+        )?;
+
+        Ok(event_key)
+    }
+}
+
+impl<M: Model> fmt::Debug for Context<M> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Context")
+            .field("name", &self.name())
+            .field("time", &self.time())
+            .field("address", &self.address)
+            .field("origin_id", &self.origin_id)
+            .finish_non_exhaustive()
+    }
+}
+
+/// Context available when building a model from a model prototype.
+///
+/// A `BuildContext` can be used to add the sub-models of a hierarchical model
+/// to the simulation bench.
+///
+/// # Examples
+///
+/// A model that multiplies its input by four using two sub-models that each
+/// multiply their input by two.
+///
+/// ```text
+///             ┌───────────────────────────────────────┐
+///             │ MyltiplyBy4                           │
+///             │   ┌─────────────┐   ┌─────────────┐   │
+///             │   │             │   │             │   │
+/// Input ●─────┼──►│ MultiplyBy2 ├──►│ MultiplyBy2 ├───┼─────► Output
+///         f64 │   │             │   │             │   │ f64
+///             │   └─────────────┘   └─────────────┘   │
+///             │                                       │
+///             └───────────────────────────────────────┘
+/// ```
+///
+/// ```
+/// use std::time::Duration;
+/// use nexosim::model::{BuildContext, Model, ProtoModel};
+/// use nexosim::ports::Output;
+/// use nexosim::simulation::Mailbox;
+///
+/// #[derive(Default)]
+/// struct MultiplyBy2 {
+///     pub output: Output<i32>,
+/// }
+/// impl MultiplyBy2 {
+///     pub async fn input(&mut self, value: i32) {
+///         self.output.send(value * 2).await;
+///     }
+/// }
+/// impl Model for MultiplyBy2 {}
+///
+/// pub struct MultiplyBy4 {
+///     // Private forwarding output.
+///     forward: Output<i32>,
+/// }
+/// impl MultiplyBy4 {
+///     pub async fn input(&mut self, value: i32) {
+///         self.forward.send(value).await;
+///     }
+/// }
+/// impl Model for MultiplyBy4 {}
+///
+/// pub struct ProtoMultiplyBy4 {
+///     pub output: Output<i32>,
+/// }
+/// impl ProtoModel for ProtoMultiplyBy4 {
+///     type Model = MultiplyBy4;
+///
+///     fn build(
+///         self,
+///         cx: &mut BuildContext<Self>)
+///     -> MultiplyBy4 {
+///         let mut mult = MultiplyBy4 { forward: Output::default() };
+///         let mut submult1 = MultiplyBy2::default();
+///
+///         // Move the prototype's output to the second multiplier.
+///         let mut submult2 = MultiplyBy2 { output: self.output };
+///
+///         // Forward the parent's model input to the first multiplier.
+///         let submult1_mbox = Mailbox::new();
+///         mult.forward.connect(MultiplyBy2::input, &submult1_mbox);
+///         
+///         // Connect the two multiplier submodels.
+///         let submult2_mbox = Mailbox::new();
+///         submult1.output.connect(MultiplyBy2::input, &submult2_mbox);
+///         
+///         // Add the submodels to the simulation.
+///         cx.add_submodel(submult1, submult1_mbox, "submultiplier 1");
+///         cx.add_submodel(submult2, submult2_mbox, "submultiplier 2");
+///
+///         mult
+///     }
+/// }
+///
+/// ```
+#[derive(Debug)]
+pub struct BuildContext<'a, P: ProtoModel> {
+    mailbox: &'a Mailbox<P::Model>,
+    name: &'a String,
+    scheduler: &'a GlobalScheduler,
+    executor: &'a Executor,
+    abort_signal: &'a Signal,
+    model_names: &'a mut Vec<String>,
+}
+
+impl<'a, P: ProtoModel> BuildContext<'a, P> {
+    /// Creates a new local context.
+    pub(crate) fn new(
+        mailbox: &'a Mailbox<P::Model>,
+        name: &'a String,
+        scheduler: &'a GlobalScheduler,
+        executor: &'a Executor,
+        abort_signal: &'a Signal,
+        model_names: &'a mut Vec<String>,
+    ) -> Self {
+        Self {
+            mailbox,
+            name,
+            scheduler,
+            executor,
+            abort_signal,
+            model_names,
+        }
+    }
+
+    /// Returns the fully qualified model instance name.
+    ///
+    /// The fully qualified name is made of the unqualified model name, if
+    /// relevant prepended by the dot-separated names of all parent models.
+    pub fn name(&self) -> &str {
+        self.name
+    }
+
+    /// Returns a handle to the model's mailbox.
+    pub fn address(&self) -> Address<P::Model> {
+        self.mailbox.address()
+    }
+
+    /// Adds a sub-model to the simulation bench.
+    ///
+    /// The `name` argument needs not be unique. It is appended to that of the
+    /// parent models' names using a dot separator (e.g.
+    /// `parent_name.child_name`) to build the fully qualified name. The use of
+    /// the dot character in the unqualified name is possible but discouraged.
+    /// If an empty string is provided, it is replaced by the string
+    /// `<unknown>`.
+    pub fn add_submodel<S: ProtoModel>(
+        &mut self,
+        model: S,
+        mailbox: Mailbox<S::Model>,
+        name: impl Into<String>,
+    ) {
+        let mut submodel_name = name.into();
+        if submodel_name.is_empty() {
+            submodel_name = String::from("<unknown>");
+        };
+        submodel_name = self.name.to_string() + "." + &submodel_name;
+
+        simulation::add_model(
+            model,
+            mailbox,
+            submodel_name,
+            self.scheduler.clone(),
+            self.executor,
+            self.abort_signal,
+            self.model_names,
+        );
+    }
+}
+
+#[cfg(all(test, not(nexosim_loom)))]
+impl<M: Model> Context<M> {
+    /// Creates a dummy context for testing purposes.
+    pub(crate) fn new_dummy() -> Self {
+        let dummy_address = Receiver::new(1).sender();
+        Context::new(
+            String::new(),
+            GlobalScheduler::new_dummy(),
+            Address(dummy_address),
+        )
+    }
+}

nexosim/src/ports.rs

@@ -0,0 +1,281 @@
+//! Ports for event and query broadcasting.
+//!
+//!
+//! # Events and queries
+//!
+//! Models can exchange data via *events* and *queries*.
+//!
+//! Events are send-and-forget messages that can be broadcast from an [`Output`]
+//! port or [`EventSource`] to an arbitrary number of *input ports* or
+//! [`EventSink`]s with a matching event type.
+//!
+//! Queries actually involve two messages: a *request* that can be broadcast
+//! from a [`Requestor`] port, a [`UniRequestor`] port or a [`QuerySource`] to
+//! an arbitrary number of *replier ports* with a matching request type, and a
+//! *reply* sent in response to such request. The response received by a
+//! [`Requestor`] port is an iterator that yields as many items (replies) as
+//! there are connected replier ports, while a [`UniRequestor`] received exactly
+//! one reply.
+//!
+//! # Model ports
+//!
+//! ## Input and replier ports
+//!
+//! Input ports and replier ports are methods that implement the [`InputFn`] or
+//! [`ReplierFn`] traits.
+//!
+//! In practice, an input port method for an event of type `T` may have any of
+//! the following signatures, where the futures returned by the `async` variants
+//! must implement `Send`:
+//!
+//! ```ignore
+//! fn(&mut self) // argument elided, implies `T=()`
+//! fn(&mut self, T)
+//! fn(&mut self, T, &mut Context<Self>)
+//! async fn(&mut self) // argument elided, implies `T=()`
+//! async fn(&mut self, T)
+//! async fn(&mut self, T, &mut Context<Self>)
+//! where
+//!     Self: Model,
+//!     T: Clone + Send + 'static,
+//!     R: Send + 'static,
+//! ```
+//!
+//! The context argument is useful for methods that need access to the
+//! simulation time or that need to schedule an action at a future date.
+//!
+//! A replier port for a request of type `T` with a reply of type `R` may in
+//! turn have any of the following signatures, where the futures must implement
+//! `Send`:
+//!
+//! ```ignore
+//! async fn(&mut self) -> R // argument elided, implies `T=()`
+//! async fn(&mut self, T) -> R
+//! async fn(&mut self, T, &mut Context<Self>) -> R
+//! where
+//!     Self: Model,
+//!     T: Clone + Send + 'static,
+//!     R: Send + 'static,
+//! ```
+//!
+//! Note that, due to type resolution ambiguities, non-async methods are not
+//! allowed for replier ports.
+//!
+//! Input and replier ports will normally be exposed as public methods by a
+//! [`Model`](crate::model::Model) so they can be connected to output and
+//! requestor ports when assembling the simulation bench. However, input ports
+//! may (and should) be defined as private methods if they are only used
+//! internally by the model, for instance to schedule future actions on itself.
+//!
+//! Changing the signature of a public input or replier port is not considered
+//! to alter the public interface of a model provided that the event, request
+//! and reply types remain the same. In particular, adding a context argument or
+//! changing a regular method to an `async` method will not cause idiomatic user
+//! code to miscompile.
+//!
+//! #### Basic example
+//!
+//! ```
+//! use nexosim::model::{Context, Model};
+//!
+//! pub struct MyModel {
+//!     // ...
+//! }
+//! impl MyModel {
+//!     pub fn my_input(&mut self, input: String, cx: &mut Context<Self>) {
+//!         // ...
+//!     }
+//!     pub async fn my_replier(&mut self, request: u32) -> bool { // context argument elided
+//!         // ...
+//!         # unimplemented!()
+//!     }
+//! }
+//! impl Model for MyModel {}
+//! ```
+//!
+//! ## Output and requestor ports
+//!
+//! Output and requestor ports can be added to a model using composition, adding
+//! [`Output`], [`Requestor`] or [`UniRequestor`] objects as members. They are
+//! parametrized by the event type, or by the request and reply types.
+//!
+//! Output ports broadcast events to all connected input ports, while requestor
+//! ports broadcast queries to, and retrieve replies from, all connected replier
+//! ports.
+//!
+//! On the surface, output and requestor ports only differ in that sending a
+//! query from a requestor port also returns an iterator over the replies from
+//! all connected ports (or a single reply in the case of [`UniRequestor`]).
+//! Sending a query is more costly, however, because of the need to wait until
+//! the connected model(s) have processed the query. In contrast, since events
+//! are buffered in the mailbox of the target model, sending an event is a
+//! fire-and-forget operation. For this reason, output ports should generally be
+//! preferred over requestor ports when possible.
+//!
+//! Models (or model prototypes, as appropriate) are expected to expose their
+//! output and requestor ports as public members so they can be connected to
+//! input and replier ports when assembling the simulation bench. Internal ports
+//! used by hierarchical models to communicate with submodels are an exception
+//! to this rule and are typically private.
+//!
+//! #### Basic example
+//!
+//! ```
+//! use nexosim::model::Model;
+//! use nexosim::ports::{Output, Requestor};
+//!
+//! pub struct MyModel {
+//!     pub my_output: Output<String>,
+//!     pub my_requestor: Requestor<u32, bool>,
+//! }
+//! impl MyModel {
+//!     // ...
+//! }
+//! impl Model for MyModel {}
+//! ```
+//!
+//! #### Example with cloned ports
+//!
+//! [`Output`] and [`Requestor`] ports are clonable. The clones are shallow
+//! copies, meaning that any modification of the ports connected to one instance
+//! is immediately reflected by its clones.
+//!
+//! Clones of output and requestor ports should be used with care: even though
+//! they uphold the usual [ordering
+//! guaranties](crate#message-ordering-guarantees), their use can lead to
+//! somewhat surprising message orderings.
+//!
+//! For instance, in the below [hierarchical
+//! model](crate::model#hierarchical-models), while message `M0` is guaranteed
+//! to reach the cloned output first, the relative arrival order of messages
+//! `M1` and `M2` forwarded by the submodels to the cloned output is not
+//! guaranteed.
+//!
+//! ```
+//! use nexosim::model::{BuildContext, Model, ProtoModel};
+//! use nexosim::ports::Output;
+//! use nexosim::simulation::Mailbox;
+//!
+//! pub struct ParentModel {
+//!     output: Output<String>,
+//!     to_child1: Output<String>,
+//!     to_child2: Output<String>,
+//! }
+//! impl ParentModel {
+//!     pub async fn trigger(&mut self) {
+//!         // M0 is guaranteed to reach the cloned output first.
+//!         self.output.send("M0".to_string()).await;
+//!
+//!         // M1 and M2 are forwarded by `Child1` and `Child2` to the cloned output
+//!         // but may reach it in any relative order.
+//!         self.to_child1.send("M1".to_string()).await;
+//!         self.to_child2.send("M2".to_string()).await;
+//!     }
+//! }
+//! impl Model for ParentModel {}
+//!
+//! pub struct ProtoParentModel {
+//!     pub output: Output<String>,
+//! }
+//! impl ProtoParentModel {
+//!     pub fn new() -> Self {
+//!         Self {
+//!             output: Default::default(),
+//!         }
+//!     }
+//! }
+//! impl ProtoModel for ProtoParentModel {
+//!     type Model = ParentModel;
+//!     fn build(self, cx: &mut BuildContext<Self>) -> ParentModel {
+//!         let child1 = ChildModel { output: self.output.clone() };
+//!         let child2 = ChildModel { output: self.output.clone() };
+//!         let mut parent = ParentModel {
+//!             output: self.output,
+//!             to_child1: Output::default(),
+//!             to_child2: Output::default(),
+//!         };
+//!
+//!         let child1_mailbox = Mailbox::new();
+//!         let child2_mailbox = Mailbox::new();
+//!         parent
+//!             .to_child1
+//!             .connect(ChildModel::input, child1_mailbox.address());
+//!         parent
+//!             .to_child2
+//!             .connect(ChildModel::input, child2_mailbox.address());
+//!
+//!         cx.add_submodel(child1, child1_mailbox, "child1");
+//!         cx.add_submodel(child2, child2_mailbox, "child2");
+//!
+//!         parent
+//!     }
+//! }
+//!
+//! pub struct ChildModel {
+//!     pub output: Output<String>,
+//! }
+//! impl ChildModel {
+//!     async fn input(&mut self, msg: String) {
+//!         self.output.send(msg).await;
+//!     }
+//! }
+//! impl Model for ChildModel {}
+//! ```
+//!
+//! # Simulation endpoints
+//!
+//! Simulation endpoints can be seen as entry and exit ports for a simulation
+//! bench.
+//!
+//! [`EventSource`] and [`QuerySource`] objects are similar to [`Output`] and
+//! [`Requestor`] ports, respectively. They can be connected to models and can
+//! be used to send events or queries to such models via
+//! [`Action`](crate::simulation::Action)s.
+//!
+//! Objects implementing the [`EventSink`] trait, such as [`EventSlot`] and
+//! [`EventBuffer`], are in turn similar to input ports. They can be connected
+//! to model outputs and collect events sent by such models.
+//!
+//!
+//! # Connections
+//!
+//! Model ports can be connected to other model ports and to simulation
+//! endpoints using the `*connect` family of methods exposed by [`Output`],
+//! [`Requestor`], [`UniRequestor`], [`EventSource`] and [`QuerySource`].
+//!
+//! Regular connections between two ports are made with the appropriate
+//! `connect` method (for instance [`Output::connect`]). Such connections
+//! broadcast events or requests from a sender port to one or several receiver
+//! ports, cloning the event or request if necessary.
+//!
+//! Sometimes, however, it may be necessary to also map the event or request to
+//! another type so it can be understood by the receiving port. While this
+//! translation could be done by a model placed between the two ports, the
+//! `map_connect` methods (for instance [`Output::map_connect`]) provide a
+//! lightweight and computationally efficient alternative. These methods take a
+//! mapping closure as argument which maps outgoing messages, and in the case of
+//! requestors, a mapping closure which maps replies.
+//!
+//! Finally, it is sometime necessary to only forward messages or requests that
+//! satisfy specific criteria. For instance, a model of a data bus may be
+//! connected to many models (the "peripherals"), but its messages are usually
+//! only addressed to selected models. The `filter_map_connect` methods (for
+//! instance [`Output::filter_map_connect`]) enable this use-case by accepting a
+//! closure that inspects the messages and determines whether they should be
+//! forwarded, possibly after being mapped to another type.
+//!
+mod input;
+mod output;
+mod sink;
+mod source;
+
+pub use input::markers;
+pub use input::{InputFn, ReplierFn};
+pub use output::{Output, Requestor, UniRequestor};
+pub use sink::{
+    blocking_event_queue::{BlockingEventQueue, BlockingEventQueueReader},
+    event_buffer::EventBuffer,
+    event_slot::EventSlot,
+    EventSink, EventSinkStream, EventSinkWriter,
+};
+pub use source::{EventSource, QuerySource, ReplyReceiver};

nexosim/src/ports/input.rs

@@ -0,0 +1,4 @@
+pub mod markers;
+mod model_fn;
+
+pub use model_fn::{InputFn, ReplierFn};

nexosim/src/ports/input/markers.rs

@@ -6,14 +6,14 @@
 pub struct WithoutArguments {}
 
 /// Marker type for regular simulation model methods that take a mutable
-/// reference to the model and a message, without scheduler argument.
+/// reference to the model and a message, without context argument.
 #[derive(Debug)]
-pub struct WithoutScheduler {}
+pub struct WithoutContext {}
 
 /// Marker type for regular simulation model methods that take a mutable
-/// reference to the model, a message and an explicit scheduler argument.
+/// reference to the model, a message and an explicit context argument.
 #[derive(Debug)]
-pub struct WithScheduler {}
+pub struct WithContext {}
 
 /// Marker type for asynchronous simulation model methods that take a mutable
 /// reference to the model, without any other argument.
@@ -21,11 +21,11 @@ pub struct WithScheduler {}
 pub struct AsyncWithoutArguments {}
 
 /// Marker type for asynchronous simulation model methods that take a mutable
-/// reference to the model and a message, without scheduler argument.
+/// reference to the model and a message, without context argument.
 #[derive(Debug)]
-pub struct AsyncWithoutScheduler {}
+pub struct AsyncWithoutContext {}
 
 /// Marker type for asynchronous simulation model methods that take a mutable
-/// reference to the model, a message and an explicit scheduler argument.
+/// reference to the model, a message and an explicit context argument.
 #[derive(Debug)]
-pub struct AsyncWithScheduler {}
+pub struct AsyncWithContext {}

nexosim/src/ports/input/model_fn.rs

@@ -2,38 +2,34 @@
 
 use std::future::{ready, Future, Ready};
 
-use crate::model::{markers, Model};
-use crate::time::Scheduler;
+use crate::model::{Context, Model};
+
+use super::markers;
 
 /// A function, method or closures that can be used as an *input port*.
 ///
 /// This trait is in particular implemented for any function or method with the
-/// following signature, where it is implicitly assumed that the function
-/// implements `Send + 'static`:
+/// following signature, where the futures returned by the `async` variants must
+/// implement `Send`:
 ///
 /// ```ignore
-/// FnOnce(&mut M, T)
-/// FnOnce(&mut M, T, &Scheduler<M>)
+/// fn(&mut M) // argument elided, implies `T=()`
+/// fn(&mut M, T)
+/// fn(&mut M, T, &mut Context<M>)
+/// async fn(&mut M) // argument elided, implies `T=()`
 /// async fn(&mut M, T)
-/// async fn(&mut M, T, &Scheduler<M>)
+/// async fn(&mut M, T, &mut Context<M>)
 /// where
-///     M: Model
-/// ```
-///
-/// It is also implemented for the following signatures when `T=()`:
-///
-/// ```ignore
-/// FnOnce(&mut M)
-/// async fn(&mut M)
-/// where
-///     M: Model
+///     M: Model,
+///     T: Clone + Send + 'static,
+///     R: Send + 'static,
 /// ```
 pub trait InputFn<'a, M: Model, T, S>: Send + 'static {
     /// The `Future` returned by the asynchronous method.
     type Future: Future<Output = ()> + Send + 'a;
 
     /// Calls the method.
-    fn call(self, model: &'a mut M, arg: T, scheduler: &'a Scheduler<M>) -> Self::Future;
+    fn call(self, model: &'a mut M, arg: T, cx: &'a mut Context<M>) -> Self::Future;
 }
 
 impl<'a, M, F> InputFn<'a, M, (), markers::WithoutArguments> for F
@@ -43,36 +39,36 @@ where
 {
     type Future = Ready<()>;
 
-    fn call(self, model: &'a mut M, _arg: (), _scheduler: &'a Scheduler<M>) -> Self::Future {
+    fn call(self, model: &'a mut M, _arg: (), _cx: &'a mut Context<M>) -> Self::Future {
         self(model);
 
         ready(())
     }
 }
 
-impl<'a, M, T, F> InputFn<'a, M, T, markers::WithoutScheduler> for F
+impl<'a, M, T, F> InputFn<'a, M, T, markers::WithoutContext> for F
 where
     M: Model,
     F: FnOnce(&'a mut M, T) + Send + 'static,
 {
     type Future = Ready<()>;
 
-    fn call(self, model: &'a mut M, arg: T, _scheduler: &'a Scheduler<M>) -> Self::Future {
+    fn call(self, model: &'a mut M, arg: T, _cx: &'a mut Context<M>) -> Self::Future {
         self(model, arg);
 
         ready(())
     }
 }
 
-impl<'a, M, T, F> InputFn<'a, M, T, markers::WithScheduler> for F
+impl<'a, M, T, F> InputFn<'a, M, T, markers::WithContext> for F
 where
     M: Model,
-    F: FnOnce(&'a mut M, T, &'a Scheduler<M>) + Send + 'static,
+    F: FnOnce(&'a mut M, T, &'a mut Context<M>) + Send + 'static,
 {
     type Future = Ready<()>;
 
-    fn call(self, model: &'a mut M, arg: T, scheduler: &'a Scheduler<M>) -> Self::Future {
-        self(model, arg, scheduler);
+    fn call(self, model: &'a mut M, arg: T, cx: &'a mut Context<M>) -> Self::Future {
+        self(model, arg, cx);
 
         ready(())
     }
@@ -86,12 +82,12 @@ where
 {
     type Future = Fut;
 
-    fn call(self, model: &'a mut M, _arg: (), _scheduler: &'a Scheduler<M>) -> Self::Future {
+    fn call(self, model: &'a mut M, _arg: (), _cx: &'a mut Context<M>) -> Self::Future {
         self(model)
     }
 }
 
-impl<'a, M, T, Fut, F> InputFn<'a, M, T, markers::AsyncWithoutScheduler> for F
+impl<'a, M, T, Fut, F> InputFn<'a, M, T, markers::AsyncWithoutContext> for F
 where
     M: Model,
     Fut: Future<Output = ()> + Send + 'a,
@@ -99,50 +95,44 @@ where
 {
     type Future = Fut;
 
-    fn call(self, model: &'a mut M, arg: T, _scheduler: &'a Scheduler<M>) -> Self::Future {
+    fn call(self, model: &'a mut M, arg: T, _cx: &'a mut Context<M>) -> Self::Future {
         self(model, arg)
     }
 }
 
-impl<'a, M, T, Fut, F> InputFn<'a, M, T, markers::AsyncWithScheduler> for F
+impl<'a, M, T, Fut, F> InputFn<'a, M, T, markers::AsyncWithContext> for F
 where
     M: Model,
     Fut: Future<Output = ()> + Send + 'a,
-    F: FnOnce(&'a mut M, T, &'a Scheduler<M>) -> Fut + Send + 'static,
+    F: FnOnce(&'a mut M, T, &'a mut Context<M>) -> Fut + Send + 'static,
 {
     type Future = Fut;
 
-    fn call(self, model: &'a mut M, arg: T, scheduler: &'a Scheduler<M>) -> Self::Future {
-        self(model, arg, scheduler)
+    fn call(self, model: &'a mut M, arg: T, cx: &'a mut Context<M>) -> Self::Future {
+        self(model, arg, cx)
     }
 }
 
 /// A function, method or closure that can be used as a *replier port*.
 ///
 /// This trait is in particular implemented for any function or method with the
-/// following signature, where it is implicitly assumed that the function
-/// implements `Send + 'static`:
+/// following signature, where the returned futures must implement `Send`:
 ///
 /// ```ignore
+/// async fn(&mut M) -> R // argument elided, implies `T=()`
 /// async fn(&mut M, T) -> R
-/// async fn(&mut M, T, &Scheduler<M>) -> R
+/// async fn(&mut M, T, &mut Context<M>) -> R
 /// where
-///     M: Model
-/// ```
-///
-/// It is also implemented for the following signatures when `T=()`:
-///
-/// ```ignore
-/// async fn(&mut M) -> R
-/// where
-///     M: Model
+///     M: Model,
+///     T: Clone + Send + 'static,
+///     R: Send + 'static,
 /// ```
 pub trait ReplierFn<'a, M: Model, T, R, S>: Send + 'static {
     /// The `Future` returned by the asynchronous method.
     type Future: Future<Output = R> + Send + 'a;
 
     /// Calls the method.
-    fn call(self, model: &'a mut M, arg: T, scheduler: &'a Scheduler<M>) -> Self::Future;
+    fn call(self, model: &'a mut M, arg: T, cx: &'a mut Context<M>) -> Self::Future;
 }
 
 impl<'a, M, R, Fut, F> ReplierFn<'a, M, (), R, markers::AsyncWithoutArguments> for F
@@ -153,12 +143,12 @@ where
 {
     type Future = Fut;
 
-    fn call(self, model: &'a mut M, _arg: (), _scheduler: &'a Scheduler<M>) -> Self::Future {
+    fn call(self, model: &'a mut M, _arg: (), _cx: &'a mut Context<M>) -> Self::Future {
         self(model)
     }
 }
 
-impl<'a, M, T, R, Fut, F> ReplierFn<'a, M, T, R, markers::AsyncWithoutScheduler> for F
+impl<'a, M, T, R, Fut, F> ReplierFn<'a, M, T, R, markers::AsyncWithoutContext> for F
 where
     M: Model,
     Fut: Future<Output = R> + Send + 'a,
@@ -166,20 +156,20 @@ where
 {
     type Future = Fut;
 
-    fn call(self, model: &'a mut M, arg: T, _scheduler: &'a Scheduler<M>) -> Self::Future {
+    fn call(self, model: &'a mut M, arg: T, _cx: &'a mut Context<M>) -> Self::Future {
         self(model, arg)
     }
 }
 
-impl<'a, M, T, R, Fut, F> ReplierFn<'a, M, T, R, markers::AsyncWithScheduler> for F
+impl<'a, M, T, R, Fut, F> ReplierFn<'a, M, T, R, markers::AsyncWithContext> for F
 where
     M: Model,
     Fut: Future<Output = R> + Send + 'a,
-    F: FnOnce(&'a mut M, T, &'a Scheduler<M>) -> Fut + Send + 'static,
+    F: FnOnce(&'a mut M, T, &'a mut Context<M>) -> Fut + Send + 'static,
 {
     type Future = Fut;
 
-    fn call(self, model: &'a mut M, arg: T, scheduler: &'a Scheduler<M>) -> Self::Future {
-        self(model, arg, scheduler)
+    fn call(self, model: &'a mut M, arg: T, cx: &'a mut Context<M>) -> Self::Future {
+        self(model, arg, cx)
     }
 }

nexosim/src/ports/output.rs

@@ -0,0 +1,418 @@
+mod broadcaster;
+mod sender;
+
+use std::fmt;
+
+use crate::model::Model;
+use crate::ports::EventSink;
+use crate::ports::{InputFn, ReplierFn};
+use crate::simulation::Address;
+use crate::util::cached_rw_lock::CachedRwLock;
+use crate::util::unwrap_or_throw::UnwrapOrThrow;
+
+use broadcaster::{EventBroadcaster, QueryBroadcaster};
+use sender::{FilterMapReplierSender, Sender};
+
+use self::sender::{
+    EventSinkSender, FilterMapEventSinkSender, FilterMapInputSender, InputSender,
+    MapEventSinkSender, MapInputSender, MapReplierSender, ReplierSender,
+};
+
+/// An output port.
+///
+/// `Output` ports can be connected to input ports, i.e. to asynchronous model
+/// methods that return no value. They broadcast events to all connected input
+/// ports.
+///
+/// When an `Output` is cloned, the information on connected ports remains
+/// shared and therefore all clones use and modify the same list of connected
+/// ports.
+#[derive(Clone)]
+pub struct Output<T: Clone + Send + 'static> {
+    broadcaster: CachedRwLock<EventBroadcaster<T>>,
+}
+
+impl<T: Clone + Send + 'static> Output<T> {
+    /// Creates a disconnected `Output` port.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Adds a connection to an input port of the model specified by the
+    /// address.
+    ///
+    /// The input port must be an asynchronous method of a model of type `M`
+    /// taking as argument a value of type `T` plus, optionally, a scheduler
+    /// reference.
+    pub fn connect<M, F, S>(&mut self, input: F, address: impl Into<Address<M>>)
+    where
+        M: Model,
+        F: for<'a> InputFn<'a, M, T, S> + Clone,
+        S: Send + 'static,
+    {
+        let sender = Box::new(InputSender::new(input, address.into().0));
+        self.broadcaster.write().unwrap().add(sender);
+    }
+
+    /// Adds a connection to an event sink such as an
+    /// [`EventSlot`](crate::ports::EventSlot) or
+    /// [`EventBuffer`](crate::ports::EventBuffer).
+    pub fn connect_sink<S: EventSink<T>>(&mut self, sink: &S) {
+        let sender = Box::new(EventSinkSender::new(sink.writer()));
+        self.broadcaster.write().unwrap().add(sender)
+    }
+
+    /// Adds an auto-converting connection to an input port of the model
+    /// specified by the address.
+    ///
+    /// Events are mapped to another type using the closure provided in
+    /// argument.
+    ///
+    /// The input port must be an asynchronous method of a model of type `M`
+    /// taking as argument a value of the type returned by the mapping
+    /// closure plus, optionally, a context reference.
+    pub fn map_connect<M, C, F, U, S>(&mut self, map: C, input: F, address: impl Into<Address<M>>)
+    where
+        M: Model,
+        C: Fn(&T) -> U + Send + Sync + 'static,
+        F: for<'a> InputFn<'a, M, U, S> + Clone,
+        U: Send + 'static,
+        S: Send + 'static,
+    {
+        let sender = Box::new(MapInputSender::new(map, input, address.into().0));
+        self.broadcaster.write().unwrap().add(sender);
+    }
+
+    /// Adds an auto-converting connection to an event sink such as an
+    /// [`EventSlot`](crate::ports::EventSlot) or
+    /// [`EventBuffer`](crate::ports::EventBuffer).
+    ///
+    /// Events are mapped to another type using the closure provided in
+    /// argument.
+    pub fn map_connect_sink<C, U, S>(&mut self, map: C, sink: &S)
+    where
+        C: Fn(&T) -> U + Send + Sync + 'static,
+        U: Send + 'static,
+        S: EventSink<U>,
+    {
+        let sender = Box::new(MapEventSinkSender::new(map, sink.writer()));
+        self.broadcaster.write().unwrap().add(sender);
+    }
+
+    /// Adds an auto-converting, filtered connection to an input port of the
+    /// model specified by the address.
+    ///
+    /// Events are mapped to another type using the closure provided in
+    /// argument, or ignored if the closure returns `None`.
+    ///
+    /// The input port must be an asynchronous method of a model of type `M`
+    /// taking as argument a value of the type returned by the mapping
+    /// closure plus, optionally, a context reference.
+    pub fn filter_map_connect<M, C, F, U, S>(
+        &mut self,
+        filter_map: C,
+        input: F,
+        address: impl Into<Address<M>>,
+    ) where
+        M: Model,
+        C: Fn(&T) -> Option<U> + Send + Sync + 'static,
+        F: for<'a> InputFn<'a, M, U, S> + Clone,
+        U: Send + 'static,
+        S: Send + 'static,
+    {
+        let sender = Box::new(FilterMapInputSender::new(
+            filter_map,
+            input,
+            address.into().0,
+        ));
+        self.broadcaster.write().unwrap().add(sender);
+    }
+
+    /// Adds an auto-converting connection to an event sink such as an
+    /// [`EventSlot`](crate::ports::EventSlot) or
+    /// [`EventBuffer`](crate::ports::EventBuffer).
+    ///
+    /// Events are mapped to another type using the closure provided in
+    /// argument.
+    pub fn filter_map_connect_sink<C, U, S>(&mut self, filter_map: C, sink: &S)
+    where
+        C: Fn(&T) -> Option<U> + Send + Sync + 'static,
+        U: Send + 'static,
+        S: EventSink<U>,
+    {
+        let sender = Box::new(FilterMapEventSinkSender::new(filter_map, sink.writer()));
+        self.broadcaster.write().unwrap().add(sender);
+    }
+
+    /// Broadcasts an event to all connected input ports.
+    pub async fn send(&mut self, arg: T) {
+        let broadcaster = self.broadcaster.write_scratchpad().unwrap();
+        broadcaster.broadcast(arg).await.unwrap_or_throw();
+    }
+}
+
+impl<T: Clone + Send + 'static> Default for Output<T> {
+    fn default() -> Self {
+        Self {
+            broadcaster: CachedRwLock::new(EventBroadcaster::default()),
+        }
+    }
+}
+
+impl<T: Clone + Send + 'static> fmt::Debug for Output<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "Output ({} connected ports)",
+            self.broadcaster.read_unsync().len()
+        )
+    }
+}
+
+/// A requestor port.
+///
+/// `Requestor` ports can be connected to replier ports, i.e. to asynchronous
+/// model methods that return a value. They broadcast queries to all connected
+/// replier ports.
+///
+/// When a `Requestor` is cloned, the information on connected ports remains
+/// shared and therefore all clones use and modify the same list of connected
+/// ports.
+#[derive(Clone)]
+pub struct Requestor<T: Clone + Send + 'static, R: Send + 'static> {
+    broadcaster: CachedRwLock<QueryBroadcaster<T, R>>,
+}
+
+impl<T: Clone + Send + 'static, R: Send + 'static> Requestor<T, R> {
+    /// Creates a disconnected `Requestor` port.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Adds a connection to a replier port of the model specified by the
+    /// address.
+    ///
+    /// The replier port must be an asynchronous method of a model of type `M`
+    /// returning a value of type `R` and taking as argument a value of type `T`
+    /// plus, optionally, a context reference.
+    pub fn connect<M, F, S>(&mut self, replier: F, address: impl Into<Address<M>>)
+    where
+        M: Model,
+        F: for<'a> ReplierFn<'a, M, T, R, S> + Clone,
+        S: Send + 'static,
+    {
+        let sender = Box::new(ReplierSender::new(replier, address.into().0));
+        self.broadcaster.write().unwrap().add(sender);
+    }
+
+    /// Adds an auto-converting connection to a replier port of the model
+    /// specified by the address.
+    ///
+    /// Queries and replies are mapped to other types using the closures
+    /// provided in argument.
+    ///
+    /// The replier port must be an asynchronous method of a model of type `M`
+    /// returning a value of the type returned by the reply mapping closure and
+    /// taking as argument a value of the type returned by the query mapping
+    /// closure plus, optionally, a context reference.
+    pub fn map_connect<M, C, D, F, U, Q, S>(
+        &mut self,
+        query_map: C,
+        reply_map: D,
+        replier: F,
+        address: impl Into<Address<M>>,
+    ) where
+        M: Model,
+        C: Fn(&T) -> U + Send + Sync + 'static,
+        D: Fn(Q) -> R + Send + Sync + 'static,
+        F: for<'a> ReplierFn<'a, M, U, Q, S> + Clone,
+        U: Send + 'static,
+        Q: Send + 'static,
+        S: Send + 'static,
+    {
+        let sender = Box::new(MapReplierSender::new(
+            query_map,
+            reply_map,
+            replier,
+            address.into().0,
+        ));
+        self.broadcaster.write().unwrap().add(sender);
+    }
+
+    /// Adds an auto-converting, filtered connection to a replier port of the
+    /// model specified by the address.
+    ///
+    /// Queries and replies are mapped to other types using the closures
+    /// provided in argument, or ignored if the query closure returns `None`.
+    ///
+    /// The replier port must be an asynchronous method of a model of type `M`
+    /// returning a value of the type returned by the reply mapping closure and
+    /// taking as argument a value of the type returned by the query mapping
+    /// closure plus, optionally, a context reference.
+    pub fn filter_map_connect<M, C, D, F, U, Q, S>(
+        &mut self,
+        query_filter_map: C,
+        reply_map: D,
+        replier: F,
+        address: impl Into<Address<M>>,
+    ) where
+        M: Model,
+        C: Fn(&T) -> Option<U> + Send + Sync + 'static,
+        D: Fn(Q) -> R + Send + Sync + 'static,
+        F: for<'a> ReplierFn<'a, M, U, Q, S> + Clone,
+        U: Send + 'static,
+        Q: Send + 'static,
+        S: Send + 'static,
+    {
+        let sender = Box::new(FilterMapReplierSender::new(
+            query_filter_map,
+            reply_map,
+            replier,
+            address.into().0,
+        ));
+        self.broadcaster.write().unwrap().add(sender);
+    }
+
+    /// Broadcasts a query to all connected replier ports.
+    pub async fn send(&mut self, arg: T) -> impl Iterator<Item = R> + '_ {
+        self.broadcaster
+            .write_scratchpad()
+            .unwrap()
+            .broadcast(arg)
+            .await
+            .unwrap_or_throw()
+    }
+}
+
+impl<T: Clone + Send + 'static, R: Send + 'static> Default for Requestor<T, R> {
+    fn default() -> Self {
+        Self {
+            broadcaster: CachedRwLock::new(QueryBroadcaster::default()),
+        }
+    }
+}
+
+impl<T: Clone + Send + 'static, R: Send + 'static> fmt::Debug for Requestor<T, R> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "Requestor ({} connected ports)",
+            self.broadcaster.read_unsync().len()
+        )
+    }
+}
+
+/// A requestor port with exactly one connection.
+///
+/// A `UniRequestor` port is connected to a replier port, i.e. to an
+/// asynchronous model method that returns a value.
+#[derive(Clone)]
+pub struct UniRequestor<T: Clone + Send + 'static, R: Send + 'static> {
+    sender: Box<dyn Sender<T, R>>,
+}
+
+impl<T: Clone + Send + 'static, R: Send + 'static> UniRequestor<T, R> {
+    /// Creates a `UniRequestor` port connected to a replier port of the model
+    /// specified by the address.
+    ///
+    /// The replier port must be an asynchronous method of a model of type `M`
+    /// returning a value of type `R` and taking as argument a value of type `T`
+    /// plus, optionally, a context reference.
+    pub fn new<M, F, S>(replier: F, address: impl Into<Address<M>>) -> Self
+    where
+        M: Model,
+        F: for<'a> ReplierFn<'a, M, T, R, S> + Clone,
+        S: Send + 'static,
+    {
+        let sender = Box::new(ReplierSender::new(replier, address.into().0));
+
+        Self { sender }
+    }
+
+    /// Creates an auto-converting `UniRequestor` port connected to a replier
+    /// port of the model specified by the address.
+    ///
+    /// Queries and replies are mapped to other types using the closures
+    /// provided in argument.
+    ///
+    /// The replier port must be an asynchronous method of a model of type `M`
+    /// returning a value of the type returned by the reply mapping closure and
+    /// taking as argument a value of the type returned by the query mapping
+    /// closure plus, optionally, a context reference.
+    pub fn with_map<M, C, D, F, U, Q, S>(
+        query_map: C,
+        reply_map: D,
+        replier: F,
+        address: impl Into<Address<M>>,
+    ) -> Self
+    where
+        M: Model,
+        C: Fn(&T) -> U + Send + Sync + 'static,
+        D: Fn(Q) -> R + Send + Sync + 'static,
+        F: for<'a> ReplierFn<'a, M, U, Q, S> + Clone,
+        U: Send + 'static,
+        Q: Send + 'static,
+        S: Send + 'static,
+    {
+        let sender = Box::new(MapReplierSender::new(
+            query_map,
+            reply_map,
+            replier,
+            address.into().0,
+        ));
+
+        Self { sender }
+    }
+
+    /// Creates an auto-converting, filtered `UniRequestor` port connected to a
+    /// replier port of the model specified by the address.
+    ///
+    /// Queries and replies are mapped to other types using the closures
+    /// provided in argument, or ignored if the query closure returns `None`.
+    ///
+    /// The replier port must be an asynchronous method of a model of type `M`
+    /// returning a value of the type returned by the reply mapping closure and
+    /// taking as argument a value of the type returned by the query mapping
+    /// closure plus, optionally, a context reference.
+    pub fn with_filter_map<M, C, D, F, U, Q, S>(
+        query_filter_map: C,
+        reply_map: D,
+        replier: F,
+        address: impl Into<Address<M>>,
+    ) -> Self
+    where
+        M: Model,
+        C: Fn(&T) -> Option<U> + Send + Sync + 'static,
+        D: Fn(Q) -> R + Send + Sync + 'static,
+        F: for<'a> ReplierFn<'a, M, U, Q, S> + Clone,
+        U: Send + 'static,
+        Q: Send + 'static,
+        S: Send + 'static,
+    {
+        let sender = Box::new(FilterMapReplierSender::new(
+            query_filter_map,
+            reply_map,
+            replier,
+            address.into().0,
+        ));
+
+        Self { sender }
+    }
+
+    /// Sends a query to the connected replier port.
+    pub async fn send(&mut self, arg: T) -> Option<R> {
+        if let Some(fut) = self.sender.send_owned(arg) {
+            let output = fut.await.unwrap_or_throw();
+
+            Some(output)
+        } else {
+            None
+        }
+    }
+}
+
+impl<T: Clone + Send + 'static, R: Send + 'static> fmt::Debug for UniRequestor<T, R> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "UniRequestor")
+    }
+}

nexosim/src/ports/output/sender.rs

@@ -0,0 +1,756 @@
+use std::future::Future;
+use std::marker::PhantomData;
+use std::mem::ManuallyDrop;
+use std::pin::Pin;
+use std::sync::Arc;
+use std::task::{Context, Poll};
+
+use dyn_clone::DynClone;
+use recycle_box::{coerce_box, RecycleBox};
+
+use crate::channel;
+use crate::channel::SendError;
+use crate::model::Model;
+use crate::ports::{EventSinkWriter, InputFn, ReplierFn};
+
+/// An event or query sender abstracting over the target model and input or
+/// replier method.
+pub(super) trait Sender<T, R>: DynClone + Send {
+    /// Asynchronously sends a message using a reference to the message.
+    fn send(&mut self, arg: &T) -> Option<RecycledFuture<'_, Result<R, SendError>>>;
+
+    /// Asynchronously sends an owned message.
+    fn send_owned(&mut self, arg: T) -> Option<RecycledFuture<'_, Result<R, SendError>>> {
+        self.send(&arg)
+    }
+}
+
+dyn_clone::clone_trait_object!(<T, R> Sender<T, R>);
+
+/// An object that can send events to an input port.
+pub(super) struct InputSender<M, F, T, S>
+where
+    M: 'static,
+{
+    func: F,
+    sender: channel::Sender<M>,
+    fut_storage: Option<RecycleBox<()>>,
+    _phantom_closure: PhantomData<fn(&mut M, T)>,
+    _phantom_closure_marker: PhantomData<S>,
+}
+
+impl<M, F, T, S> InputSender<M, F, T, S>
+where
+    M: 'static,
+{
+    pub(super) fn new(func: F, sender: channel::Sender<M>) -> Self {
+        Self {
+            func,
+            sender,
+            fut_storage: None,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+impl<M, F, T, S> Sender<T, ()> for InputSender<M, F, T, S>
+where
+    M: Model,
+    F: for<'a> InputFn<'a, M, T, S> + Clone,
+    T: Clone + Send + 'static,
+    S: Send,
+{
+    fn send(&mut self, arg: &T) -> Option<RecycledFuture<'_, Result<(), SendError>>> {
+        self.send_owned(arg.clone())
+    }
+
+    fn send_owned(&mut self, arg: T) -> Option<RecycledFuture<'_, Result<(), SendError>>> {
+        let func = self.func.clone();
+
+        let fut = self.sender.send(move |model, scheduler, recycle_box| {
+            let fut = func.call(model, arg, scheduler);
+
+            coerce_box!(RecycleBox::recycle(recycle_box, fut))
+        });
+
+        Some(RecycledFuture::new(&mut self.fut_storage, fut))
+    }
+}
+
+impl<M, F, T, S> Clone for InputSender<M, F, T, S>
+where
+    M: 'static,
+    F: Clone,
+{
+    fn clone(&self) -> Self {
+        Self {
+            func: self.func.clone(),
+            sender: self.sender.clone(),
+            fut_storage: None,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+/// An object that can send mapped events to an input port.
+pub(super) struct MapInputSender<M, C, F, T, U, S>
+where
+    M: 'static,
+{
+    map: Arc<C>,
+    func: F,
+    sender: channel::Sender<M>,
+    fut_storage: Option<RecycleBox<()>>,
+    _phantom_map: PhantomData<fn(T) -> U>,
+    _phantom_closure: PhantomData<fn(&mut M, U)>,
+    _phantom_closure_marker: PhantomData<S>,
+}
+
+impl<M, C, F, T, U, S> MapInputSender<M, C, F, T, U, S>
+where
+    M: 'static,
+{
+    pub(super) fn new(map: C, func: F, sender: channel::Sender<M>) -> Self {
+        Self {
+            map: Arc::new(map),
+            func,
+            sender,
+            fut_storage: None,
+            _phantom_map: PhantomData,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+impl<M, C, F, T, U, S> Sender<T, ()> for MapInputSender<M, C, F, T, U, S>
+where
+    M: Model,
+    C: Fn(&T) -> U + Send + Sync,
+    F: for<'a> InputFn<'a, M, U, S> + Clone,
+    T: Send + 'static,
+    U: Send + 'static,
+    S: Send,
+{
+    fn send(&mut self, arg: &T) -> Option<RecycledFuture<'_, Result<(), SendError>>> {
+        let func = self.func.clone();
+        let arg = (self.map)(arg);
+
+        let fut = self.sender.send(move |model, scheduler, recycle_box| {
+            let fut = func.call(model, arg, scheduler);
+
+            coerce_box!(RecycleBox::recycle(recycle_box, fut))
+        });
+
+        Some(RecycledFuture::new(&mut self.fut_storage, fut))
+    }
+}
+
+impl<M, C, F, T, U, S> Clone for MapInputSender<M, C, F, T, U, S>
+where
+    M: 'static,
+    F: Clone,
+{
+    fn clone(&self) -> Self {
+        Self {
+            map: self.map.clone(),
+            func: self.func.clone(),
+            sender: self.sender.clone(),
+            fut_storage: None,
+            _phantom_map: PhantomData,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+/// An object that can filter and send mapped events to an input port.
+pub(super) struct FilterMapInputSender<M, C, F, T, U, S>
+where
+    M: 'static,
+{
+    filter_map: Arc<C>,
+    func: F,
+    sender: channel::Sender<M>,
+    fut_storage: Option<RecycleBox<()>>,
+    _phantom_filter_map: PhantomData<fn(T) -> Option<U>>,
+    _phantom_closure: PhantomData<fn(&mut M, U)>,
+    _phantom_closure_marker: PhantomData<S>,
+}
+
+impl<M, C, F, T, U, S> FilterMapInputSender<M, C, F, T, U, S>
+where
+    M: 'static,
+{
+    pub(super) fn new(filter_map: C, func: F, sender: channel::Sender<M>) -> Self {
+        Self {
+            filter_map: Arc::new(filter_map),
+            func,
+            sender,
+            fut_storage: None,
+            _phantom_filter_map: PhantomData,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+impl<M, C, F, T, U, S> Sender<T, ()> for FilterMapInputSender<M, C, F, T, U, S>
+where
+    M: Model,
+    C: Fn(&T) -> Option<U> + Send + Sync,
+    F: for<'a> InputFn<'a, M, U, S> + Clone,
+    T: Send + 'static,
+    U: Send + 'static,
+    S: Send,
+{
+    fn send(&mut self, arg: &T) -> Option<RecycledFuture<'_, Result<(), SendError>>> {
+        (self.filter_map)(arg).map(|arg| {
+            let func = self.func.clone();
+
+            let fut = self.sender.send(move |model, scheduler, recycle_box| {
+                let fut = func.call(model, arg, scheduler);
+
+                coerce_box!(RecycleBox::recycle(recycle_box, fut))
+            });
+
+            RecycledFuture::new(&mut self.fut_storage, fut)
+        })
+    }
+}
+
+impl<M, C, F, T, U, S> Clone for FilterMapInputSender<M, C, F, T, U, S>
+where
+    M: 'static,
+    F: Clone,
+{
+    fn clone(&self) -> Self {
+        Self {
+            filter_map: self.filter_map.clone(),
+            func: self.func.clone(),
+            sender: self.sender.clone(),
+            fut_storage: None,
+            _phantom_filter_map: PhantomData,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+/// An object that can send an event to an event sink.
+pub(super) struct EventSinkSender<T, W> {
+    writer: W,
+    fut_storage: Option<RecycleBox<()>>,
+    _phantom_event: PhantomData<T>,
+}
+
+impl<T, W> EventSinkSender<T, W> {
+    pub(super) fn new(writer: W) -> Self {
+        Self {
+            writer,
+            fut_storage: None,
+            _phantom_event: PhantomData,
+        }
+    }
+}
+
+impl<T, W> Sender<T, ()> for EventSinkSender<T, W>
+where
+    T: Clone + Send + 'static,
+    W: EventSinkWriter<T>,
+{
+    fn send(&mut self, arg: &T) -> Option<RecycledFuture<'_, Result<(), SendError>>> {
+        self.send_owned(arg.clone())
+    }
+
+    fn send_owned(&mut self, arg: T) -> Option<RecycledFuture<'_, Result<(), SendError>>> {
+        let writer = &mut self.writer;
+
+        Some(RecycledFuture::new(&mut self.fut_storage, async move {
+            writer.write(arg);
+
+            Ok(())
+        }))
+    }
+}
+
+impl<T, W: Clone> Clone for EventSinkSender<T, W> {
+    fn clone(&self) -> Self {
+        Self {
+            writer: self.writer.clone(),
+            fut_storage: None,
+            _phantom_event: PhantomData,
+        }
+    }
+}
+
+/// An object that can send mapped events to an event sink.
+pub(super) struct MapEventSinkSender<T, U, W, C>
+where
+    C: Fn(&T) -> U,
+{
+    writer: W,
+    map: Arc<C>,
+    fut_storage: Option<RecycleBox<()>>,
+    _phantom_event: PhantomData<T>,
+}
+
+impl<T, U, W, C> MapEventSinkSender<T, U, W, C>
+where
+    C: Fn(&T) -> U,
+{
+    pub(super) fn new(map: C, writer: W) -> Self {
+        Self {
+            writer,
+            map: Arc::new(map),
+            fut_storage: None,
+            _phantom_event: PhantomData,
+        }
+    }
+}
+
+impl<T, U, W, C> Sender<T, ()> for MapEventSinkSender<T, U, W, C>
+where
+    T: Send + 'static,
+    U: Send + 'static,
+    C: Fn(&T) -> U + Send + Sync,
+    W: EventSinkWriter<U>,
+{
+    fn send(&mut self, arg: &T) -> Option<RecycledFuture<'_, Result<(), SendError>>> {
+        let writer = &mut self.writer;
+        let arg = (self.map)(arg);
+
+        Some(RecycledFuture::new(&mut self.fut_storage, async move {
+            writer.write(arg);
+
+            Ok(())
+        }))
+    }
+}
+
+impl<T, U, W, C> Clone for MapEventSinkSender<T, U, W, C>
+where
+    C: Fn(&T) -> U,
+    W: Clone,
+{
+    fn clone(&self) -> Self {
+        Self {
+            writer: self.writer.clone(),
+            map: self.map.clone(),
+            fut_storage: None,
+            _phantom_event: PhantomData,
+        }
+    }
+}
+
+/// An object that can filter and send mapped events to an event sink.
+pub(super) struct FilterMapEventSinkSender<T, U, W, C>
+where
+    C: Fn(&T) -> Option<U>,
+{
+    writer: W,
+    filter_map: Arc<C>,
+    fut_storage: Option<RecycleBox<()>>,
+    _phantom_event: PhantomData<T>,
+}
+
+impl<T, U, W, C> FilterMapEventSinkSender<T, U, W, C>
+where
+    C: Fn(&T) -> Option<U>,
+{
+    pub(super) fn new(filter_map: C, writer: W) -> Self {
+        Self {
+            writer,
+            filter_map: Arc::new(filter_map),
+            fut_storage: None,
+            _phantom_event: PhantomData,
+        }
+    }
+}
+
+impl<T, U, W, C> Sender<T, ()> for FilterMapEventSinkSender<T, U, W, C>
+where
+    T: Send + 'static,
+    U: Send + 'static,
+    C: Fn(&T) -> Option<U> + Send + Sync,
+    W: EventSinkWriter<U>,
+{
+    fn send(&mut self, arg: &T) -> Option<RecycledFuture<'_, Result<(), SendError>>> {
+        let writer = &mut self.writer;
+
+        (self.filter_map)(arg).map(|arg| {
+            RecycledFuture::new(&mut self.fut_storage, async move {
+                writer.write(arg);
+
+                Ok(())
+            })
+        })
+    }
+}
+
+impl<T, U, W, C> Clone for FilterMapEventSinkSender<T, U, W, C>
+where
+    C: Fn(&T) -> Option<U>,
+    W: Clone,
+{
+    fn clone(&self) -> Self {
+        Self {
+            writer: self.writer.clone(),
+            filter_map: self.filter_map.clone(),
+            fut_storage: None,
+            _phantom_event: PhantomData,
+        }
+    }
+}
+
+/// An object that can send requests to a replier port and retrieve responses.
+pub(super) struct ReplierSender<M, F, T, R, S>
+where
+    M: Model,
+{
+    func: F,
+    sender: channel::Sender<M>,
+    receiver: multishot::Receiver<R>,
+    fut_storage: Option<RecycleBox<()>>,
+    _phantom_closure: PhantomData<fn(&mut M, T) -> R>,
+    _phantom_closure_marker: PhantomData<S>,
+}
+
+impl<M, F, T, R, S> ReplierSender<M, F, T, R, S>
+where
+    M: Model,
+{
+    pub(super) fn new(func: F, sender: channel::Sender<M>) -> Self {
+        Self {
+            func,
+            sender,
+            receiver: multishot::Receiver::new(),
+            fut_storage: None,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+impl<M, F, T, R, S> Sender<T, R> for ReplierSender<M, F, T, R, S>
+where
+    M: Model,
+    F: for<'a> ReplierFn<'a, M, T, R, S> + Clone,
+    T: Clone + Send + 'static,
+    R: Send + 'static,
+    S: Send,
+{
+    fn send(&mut self, arg: &T) -> Option<RecycledFuture<'_, Result<R, SendError>>> {
+        self.send_owned(arg.clone())
+    }
+
+    fn send_owned(&mut self, arg: T) -> Option<RecycledFuture<'_, Result<R, SendError>>> {
+        let func = self.func.clone();
+        let sender = &mut self.sender;
+        let reply_receiver = &mut self.receiver;
+        let fut_storage = &mut self.fut_storage;
+
+        // The previous future generated by this method should have been polled
+        // to completion so a new sender should be readily available.
+        let reply_sender = reply_receiver.sender().unwrap();
+
+        let send_fut = sender.send(move |model, scheduler, recycle_box| {
+            let fut = async move {
+                let reply = func.call(model, arg, scheduler).await;
+                reply_sender.send(reply);
+            };
+
+            coerce_box!(RecycleBox::recycle(recycle_box, fut))
+        });
+
+        Some(RecycledFuture::new(fut_storage, async move {
+            // Send the message.
+            send_fut.await?;
+
+            // Wait until the message is processed and the reply is sent back.
+            // If an error is received, it most likely means the mailbox was
+            // dropped before the message was processed.
+            reply_receiver.recv().await.map_err(|_| SendError)
+        }))
+    }
+}
+
+impl<M, F, T, R, S> Clone for ReplierSender<M, F, T, R, S>
+where
+    M: Model,
+    F: Clone,
+{
+    fn clone(&self) -> Self {
+        Self {
+            func: self.func.clone(),
+            sender: self.sender.clone(),
+            receiver: multishot::Receiver::new(),
+            fut_storage: None,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+/// An object that can send mapped requests to a replier port and retrieve
+/// mapped responses.
+pub(super) struct MapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: Model,
+{
+    query_map: Arc<C>,
+    reply_map: Arc<D>,
+    func: F,
+    sender: channel::Sender<M>,
+    receiver: multishot::Receiver<Q>,
+    fut_storage: Option<RecycleBox<()>>,
+    _phantom_query_map: PhantomData<fn(T) -> U>,
+    _phantom_reply_map: PhantomData<fn(Q) -> R>,
+    _phantom_closure: PhantomData<fn(&mut M, U) -> Q>,
+    _phantom_closure_marker: PhantomData<S>,
+}
+
+impl<M, C, D, F, T, R, U, Q, S> MapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: Model,
+{
+    pub(super) fn new(query_map: C, reply_map: D, func: F, sender: channel::Sender<M>) -> Self {
+        Self {
+            query_map: Arc::new(query_map),
+            reply_map: Arc::new(reply_map),
+            func,
+            sender,
+            receiver: multishot::Receiver::new(),
+            fut_storage: None,
+            _phantom_query_map: PhantomData,
+            _phantom_reply_map: PhantomData,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+impl<M, C, D, F, T, R, U, Q, S> Sender<T, R> for MapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: Model,
+    C: Fn(&T) -> U + Send + Sync,
+    D: Fn(Q) -> R + Send + Sync,
+    F: for<'a> ReplierFn<'a, M, U, Q, S> + Clone,
+    T: Send + 'static,
+    R: Send + 'static,
+    U: Send + 'static,
+    Q: Send + 'static,
+    S: Send,
+{
+    fn send(&mut self, arg: &T) -> Option<RecycledFuture<'_, Result<R, SendError>>> {
+        let func = self.func.clone();
+        let arg = (self.query_map)(arg);
+        let sender = &mut self.sender;
+        let reply_receiver = &mut self.receiver;
+        let fut_storage = &mut self.fut_storage;
+        let reply_map = &*self.reply_map;
+
+        // The previous future generated by this method should have been polled
+        // to completion so a new sender should be readily available.
+        let reply_sender = reply_receiver.sender().unwrap();
+
+        let send_fut = sender.send(move |model, scheduler, recycle_box| {
+            let fut = async move {
+                let reply = func.call(model, arg, scheduler).await;
+                reply_sender.send(reply);
+            };
+
+            coerce_box!(RecycleBox::recycle(recycle_box, fut))
+        });
+
+        Some(RecycledFuture::new(fut_storage, async move {
+            // Send the message.
+            send_fut.await?;
+
+            // Wait until the message is processed and the reply is sent back.
+            // If an error is received, it most likely means the mailbox was
+            // dropped before the message was processed.
+            reply_receiver
+                .recv()
+                .await
+                .map_err(|_| SendError)
+                .map(reply_map)
+        }))
+    }
+}
+
+impl<M, C, D, F, T, R, U, Q, S> Clone for MapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: Model,
+    F: Clone,
+{
+    fn clone(&self) -> Self {
+        Self {
+            query_map: self.query_map.clone(),
+            reply_map: self.reply_map.clone(),
+            func: self.func.clone(),
+            sender: self.sender.clone(),
+            receiver: multishot::Receiver::new(),
+            fut_storage: None,
+            _phantom_query_map: PhantomData,
+            _phantom_reply_map: PhantomData,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+/// An object that can filter and send mapped requests to a replier port and
+/// retrieve mapped responses.
+pub(super) struct FilterMapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: Model,
+{
+    query_filter_map: Arc<C>,
+    reply_map: Arc<D>,
+    func: F,
+    sender: channel::Sender<M>,
+    receiver: multishot::Receiver<Q>,
+    fut_storage: Option<RecycleBox<()>>,
+    _phantom_query_map: PhantomData<fn(T) -> U>,
+    _phantom_reply_map: PhantomData<fn(Q) -> R>,
+    _phantom_closure: PhantomData<fn(&mut M, U) -> Q>,
+    _phantom_closure_marker: PhantomData<S>,
+}
+
+impl<M, C, D, F, T, R, U, Q, S> FilterMapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: Model,
+{
+    pub(super) fn new(
+        query_filter_map: C,
+        reply_map: D,
+        func: F,
+        sender: channel::Sender<M>,
+    ) -> Self {
+        Self {
+            query_filter_map: Arc::new(query_filter_map),
+            reply_map: Arc::new(reply_map),
+            func,
+            sender,
+            receiver: multishot::Receiver::new(),
+            fut_storage: None,
+            _phantom_query_map: PhantomData,
+            _phantom_reply_map: PhantomData,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+impl<M, C, D, F, T, R, U, Q, S> Sender<T, R> for FilterMapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: Model,
+    C: Fn(&T) -> Option<U> + Send + Sync,
+    D: Fn(Q) -> R + Send + Sync,
+    F: for<'a> ReplierFn<'a, M, U, Q, S> + Clone,
+    T: Send + 'static,
+    R: Send + 'static,
+    U: Send + 'static,
+    Q: Send + 'static,
+    S: Send,
+{
+    fn send(&mut self, arg: &T) -> Option<RecycledFuture<'_, Result<R, SendError>>> {
+        (self.query_filter_map)(arg).map(|arg| {
+            let func = self.func.clone();
+            let sender = &mut self.sender;
+            let reply_receiver = &mut self.receiver;
+            let fut_storage = &mut self.fut_storage;
+            let reply_map = &*self.reply_map;
+
+            // The previous future generated by this method should have been polled
+            // to completion so a new sender should be readily available.
+            let reply_sender = reply_receiver.sender().unwrap();
+
+            let send_fut = sender.send(move |model, scheduler, recycle_box| {
+                let fut = async move {
+                    let reply = func.call(model, arg, scheduler).await;
+                    reply_sender.send(reply);
+                };
+
+                coerce_box!(RecycleBox::recycle(recycle_box, fut))
+            });
+
+            RecycledFuture::new(fut_storage, async move {
+                // Send the message.
+                send_fut.await?;
+
+                // Wait until the message is processed and the reply is sent back.
+                // If an error is received, it most likely means the mailbox was
+                // dropped before the message was processed.
+                reply_receiver
+                    .recv()
+                    .await
+                    .map_err(|_| SendError)
+                    .map(reply_map)
+            })
+        })
+    }
+}
+
+impl<M, C, D, F, T, R, U, Q, S> Clone for FilterMapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: Model,
+    F: Clone,
+{
+    fn clone(&self) -> Self {
+        Self {
+            query_filter_map: self.query_filter_map.clone(),
+            reply_map: self.reply_map.clone(),
+            func: self.func.clone(),
+            sender: self.sender.clone(),
+            receiver: multishot::Receiver::new(),
+            fut_storage: None,
+            _phantom_query_map: PhantomData,
+            _phantom_reply_map: PhantomData,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+pub(super) struct RecycledFuture<'a, T> {
+    fut: ManuallyDrop<Pin<RecycleBox<dyn Future<Output = T> + Send + 'a>>>,
+    lender_box: &'a mut Option<RecycleBox<()>>,
+}
+impl<'a, T> RecycledFuture<'a, T> {
+    pub(super) fn new<F: Future<Output = T> + Send + 'a>(
+        lender_box: &'a mut Option<RecycleBox<()>>,
+        fut: F,
+    ) -> Self {
+        let vacated_box = lender_box.take().unwrap_or_else(|| RecycleBox::new(()));
+        let fut: RecycleBox<dyn Future<Output = T> + Send + 'a> =
+            coerce_box!(RecycleBox::recycle(vacated_box, fut));
+
+        Self {
+            fut: ManuallyDrop::new(RecycleBox::into_pin(fut)),
+            lender_box,
+        }
+    }
+}
+
+impl<T> Drop for RecycledFuture<'_, T> {
+    fn drop(&mut self) {
+        // Return the box to the lender.
+        //
+        // Safety: taking the `fut` member is safe since it is never used again.
+        *self.lender_box = Some(RecycleBox::vacate_pinned(unsafe {
+            ManuallyDrop::take(&mut self.fut)
+        }));
+    }
+}
+
+impl<T> Future for RecycledFuture<'_, T> {
+    type Output = T;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.fut.as_mut().poll(cx)
+    }
+}

nexosim/src/ports/sink.rs

@@ -0,0 +1,58 @@
+pub(crate) mod blocking_event_queue;
+pub(crate) mod event_buffer;
+pub(crate) mod event_slot;
+
+/// A simulation endpoint that can receive events sent by model outputs.
+///
+/// An `EventSink` can be thought of as a self-standing input meant to
+/// externally monitor the simulated system.
+pub trait EventSink<T> {
+    /// Writer handle to an event sink.
+    type Writer: EventSinkWriter<T>;
+
+    /// Returns the writer handle associated to this sink.
+    fn writer(&self) -> Self::Writer;
+}
+
+/// A writer handle to an event sink.
+pub trait EventSinkWriter<T>: Clone + Send + Sync + 'static {
+    /// Writes a value to the associated sink.
+    fn write(&self, event: T);
+}
+
+/// An iterator over collected events with the ability to pause and resume event
+/// collection.
+///
+/// An `EventSinkStream` will typically be implemented on an [`EventSink`] for
+/// which it will constitute a draining iterator.
+pub trait EventSinkStream: Iterator {
+    /// Starts or resumes the collection of new events.
+    fn open(&mut self);
+
+    /// Pauses the collection of new events.
+    ///
+    /// Events that were previously in the stream remain available.
+    fn close(&mut self);
+
+    /// This is a stop-gap method that serves the exact same purpose as
+    /// `Iterator::try_fold` but is specialized for `Result` rather than the
+    /// `Try` trait so it can be implemented on stable Rust.
+    ///
+    /// It makes it possible to provide a faster implementation when the event
+    /// sink stream can be iterated over more rapidly than by repeatably calling
+    /// `Iterator::next`, for instance if the implementation of the stream
+    /// relies on a mutex that must be locked on each call.
+    ///
+    /// It is not publicly implementable because it may be removed at any time
+    /// once the `Try` trait is stabilized, without regard for backward
+    /// compatibility.
+    #[doc(hidden)]
+    #[allow(private_interfaces)]
+    fn __try_fold<B, F, E>(&mut self, init: B, f: F) -> Result<B, E>
+    where
+        Self: Sized,
+        F: FnMut(B, Self::Item) -> Result<B, E>,
+    {
+        Iterator::try_fold(self, init, f)
+    }
+}

nexosim/src/ports/sink/blocking_event_queue.rs

@@ -0,0 +1,145 @@
+use std::fmt;
+use std::iter::FusedIterator;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::mpsc::{channel, Receiver, Sender};
+use std::sync::Arc;
+
+use super::{EventSink, EventSinkStream, EventSinkWriter};
+
+/// A blocking event queue with an unbounded size.
+///
+/// Implements [`EventSink`].
+///
+/// Note that [`EventSinkStream`] is implemented by
+/// [`BlockingEventQueueReader`], created with the
+/// [`BlockingEventQueue::into_reader`] method.
+pub struct BlockingEventQueue<T> {
+    is_open: Arc<AtomicBool>,
+    sender: Sender<T>,
+    receiver: Receiver<T>,
+}
+
+impl<T> BlockingEventQueue<T> {
+    /// Creates an open `BlockingEventQueue`.
+    pub fn new() -> Self {
+        Self::new_with_state(true)
+    }
+
+    /// Creates a closed `BlockingEventQueue`.
+    pub fn new_closed() -> Self {
+        Self::new_with_state(false)
+    }
+
+    /// Returns a consumer handle.
+    pub fn into_reader(self) -> BlockingEventQueueReader<T> {
+        BlockingEventQueueReader {
+            is_open: self.is_open,
+            receiver: self.receiver,
+        }
+    }
+
+    /// Creates a new `BlockingEventQueue` in the specified state.
+    fn new_with_state(is_open: bool) -> Self {
+        let (sender, receiver) = channel();
+        Self {
+            is_open: Arc::new(AtomicBool::new(is_open)),
+            sender,
+            receiver,
+        }
+    }
+}
+
+impl<T: Send + 'static> EventSink<T> for BlockingEventQueue<T> {
+    type Writer = BlockingEventQueueWriter<T>;
+
+    fn writer(&self) -> Self::Writer {
+        BlockingEventQueueWriter {
+            is_open: self.is_open.clone(),
+            sender: self.sender.clone(),
+        }
+    }
+}
+
+impl<T> Default for BlockingEventQueue<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<T> fmt::Debug for BlockingEventQueue<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("BlockingEventQueue").finish_non_exhaustive()
+    }
+}
+
+/// A consumer handle of a `BlockingEventQueue`.
+///
+/// Implements [`EventSinkStream`]. Calls to the iterator's `next` method are
+/// blocking. `None` is returned when all writer handles have been dropped.
+pub struct BlockingEventQueueReader<T> {
+    is_open: Arc<AtomicBool>,
+    receiver: Receiver<T>,
+}
+
+impl<T> Iterator for BlockingEventQueueReader<T> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.receiver.recv() {
+            Ok(event) => Some(event),
+            Err(_) => None,
+        }
+    }
+}
+
+impl<T> FusedIterator for BlockingEventQueueReader<T> {}
+
+impl<T: Send + 'static> EventSinkStream for BlockingEventQueueReader<T> {
+    fn open(&mut self) {
+        self.is_open.store(true, Ordering::Relaxed);
+    }
+
+    fn close(&mut self) {
+        self.is_open.store(false, Ordering::Relaxed);
+    }
+}
+
+impl<T> fmt::Debug for BlockingEventQueueReader<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("BlockingEventQueueReader")
+            .finish_non_exhaustive()
+    }
+}
+
+/// A producer handle of a `BlockingEventQueue`.
+pub struct BlockingEventQueueWriter<T> {
+    is_open: Arc<AtomicBool>,
+    sender: Sender<T>,
+}
+
+impl<T: Send + 'static> EventSinkWriter<T> for BlockingEventQueueWriter<T> {
+    /// Pushes an event onto the queue.
+    fn write(&self, event: T) {
+        if !self.is_open.load(Ordering::Relaxed) {
+            return;
+        }
+        // Ignore sending failure.
+        let _ = self.sender.send(event);
+    }
+}
+
+impl<T> Clone for BlockingEventQueueWriter<T> {
+    fn clone(&self) -> Self {
+        Self {
+            is_open: self.is_open.clone(),
+            sender: self.sender.clone(),
+        }
+    }
+}
+
+impl<T> fmt::Debug for BlockingEventQueueWriter<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("BlockingEventQueueWriter")
+            .finish_non_exhaustive()
+    }
+}

nexosim/src/ports/sink/event_buffer.rs

@@ -0,0 +1,149 @@
+use std::collections::VecDeque;
+use std::fmt;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::{Arc, Mutex};
+
+use super::{EventSink, EventSinkStream, EventSinkWriter};
+
+/// The shared data of an `EventBuffer`.
+struct Inner<T> {
+    capacity: usize,
+    is_open: AtomicBool,
+    buffer: Mutex<VecDeque<T>>,
+}
+
+/// An iterator implementing [`EventSink`] and [`EventSinkStream`], backed by a
+/// fixed-capacity buffer.
+///
+/// If the maximum capacity is exceeded, older events are overwritten. Events
+/// are returned in first-in-first-out order. Note that even if the iterator
+/// returns `None`, it may still produce more items in the future (in other
+/// words, it is not a [`FusedIterator`](std::iter::FusedIterator)).
+pub struct EventBuffer<T> {
+    inner: Arc<Inner<T>>,
+}
+
+impl<T> EventBuffer<T> {
+    /// Default capacity when constructed with `new`.
+    pub const DEFAULT_CAPACITY: usize = 16;
+
+    /// Creates an open `EventBuffer` with the default capacity.
+    pub fn new() -> Self {
+        Self::with_capacity(Self::DEFAULT_CAPACITY)
+    }
+
+    /// Creates a closed `EventBuffer` with the default capacity.
+    pub fn new_closed() -> Self {
+        Self::with_capacity_closed(Self::DEFAULT_CAPACITY)
+    }
+
+    /// Creates an open `EventBuffer` with the specified capacity.
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self {
+            inner: Arc::new(Inner {
+                capacity,
+                is_open: AtomicBool::new(true),
+                buffer: Mutex::new(VecDeque::new()),
+            }),
+        }
+    }
+
+    /// Creates a closed `EventBuffer` with the specified capacity.
+    pub fn with_capacity_closed(capacity: usize) -> Self {
+        Self {
+            inner: Arc::new(Inner {
+                capacity,
+                is_open: AtomicBool::new(false),
+                buffer: Mutex::new(VecDeque::new()),
+            }),
+        }
+    }
+}
+
+impl<T: Send + 'static> EventSink<T> for EventBuffer<T> {
+    type Writer = EventBufferWriter<T>;
+
+    fn writer(&self) -> Self::Writer {
+        EventBufferWriter {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl<T> Iterator for EventBuffer<T> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.buffer.lock().unwrap().pop_front()
+    }
+}
+
+impl<T: Send + 'static> EventSinkStream for EventBuffer<T> {
+    fn open(&mut self) {
+        self.inner.is_open.store(true, Ordering::Relaxed);
+    }
+
+    fn close(&mut self) {
+        self.inner.is_open.store(false, Ordering::Relaxed);
+    }
+
+    #[doc(hidden)]
+    #[allow(private_interfaces)]
+    fn __try_fold<B, F, E>(&mut self, init: B, f: F) -> Result<B, E>
+    where
+        Self: Sized,
+        F: FnMut(B, Self::Item) -> Result<B, E>,
+    {
+        let mut inner = self.inner.buffer.lock().unwrap();
+        let mut drain = inner.drain(..);
+
+        drain.try_fold(init, f)
+    }
+}
+
+impl<T> Default for EventBuffer<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<T> fmt::Debug for EventBuffer<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("EventBuffer").finish_non_exhaustive()
+    }
+}
+
+/// A producer handle of an `EventStream`.
+pub struct EventBufferWriter<T> {
+    inner: Arc<Inner<T>>,
+}
+
+impl<T: Send + 'static> EventSinkWriter<T> for EventBufferWriter<T> {
+    /// Pushes an event onto the queue.
+    fn write(&self, event: T) {
+        if !self.inner.is_open.load(Ordering::Relaxed) {
+            return;
+        }
+
+        let mut buffer = self.inner.buffer.lock().unwrap();
+        if buffer.len() == self.inner.capacity {
+            buffer.pop_front();
+        }
+
+        buffer.push_back(event);
+    }
+}
+
+impl<T> Clone for EventBufferWriter<T> {
+    fn clone(&self) -> Self {
+        Self {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl<T> fmt::Debug for EventBufferWriter<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("EventBufferWriter").finish_non_exhaustive()
+    }
+}

nexosim/src/ports/sink/event_slot.rs

@@ -0,0 +1,129 @@
+use std::fmt;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::{Arc, Mutex, TryLockError, TryLockResult};
+
+use super::{EventSink, EventSinkStream, EventSinkWriter};
+
+/// The shared data of an `EventBuffer`.
+struct Inner<T> {
+    is_open: AtomicBool,
+    slot: Mutex<Option<T>>,
+}
+
+/// An iterator implementing [`EventSink`] and [`EventSinkStream`] that only
+/// keeps the last event.
+///
+/// Once the value is read, the iterator will return `None` until a new value is
+/// received. If the slot contains a value when a new value is received, the
+/// previous value is overwritten.
+pub struct EventSlot<T> {
+    inner: Arc<Inner<T>>,
+}
+
+impl<T> EventSlot<T> {
+    /// Creates an open `EventSlot`.
+    pub fn new() -> Self {
+        Self {
+            inner: Arc::new(Inner {
+                is_open: AtomicBool::new(true),
+                slot: Mutex::new(None),
+            }),
+        }
+    }
+
+    /// Creates a closed `EventSlot`.
+    pub fn new_closed() -> Self {
+        Self {
+            inner: Arc::new(Inner {
+                is_open: AtomicBool::new(false),
+                slot: Mutex::new(None),
+            }),
+        }
+    }
+}
+
+impl<T: Send + 'static> EventSink<T> for EventSlot<T> {
+    type Writer = EventSlotWriter<T>;
+
+    /// Returns a writer handle.
+    fn writer(&self) -> EventSlotWriter<T> {
+        EventSlotWriter {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl<T> Iterator for EventSlot<T> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.inner.slot.try_lock() {
+            TryLockResult::Ok(mut v) => v.take(),
+            TryLockResult::Err(TryLockError::WouldBlock) => None,
+            TryLockResult::Err(TryLockError::Poisoned(_)) => panic!(),
+        }
+    }
+}
+
+impl<T: Send + 'static> EventSinkStream for EventSlot<T> {
+    fn open(&mut self) {
+        self.inner.is_open.store(true, Ordering::Relaxed);
+    }
+    fn close(&mut self) {
+        self.inner.is_open.store(false, Ordering::Relaxed);
+    }
+}
+
+impl<T> Default for EventSlot<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<T> fmt::Debug for EventSlot<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("EventSlot").finish_non_exhaustive()
+    }
+}
+
+/// A writer handle of an `EventSlot`.
+pub struct EventSlotWriter<T> {
+    inner: Arc<Inner<T>>,
+}
+
+impl<T: Send + 'static> EventSinkWriter<T> for EventSlotWriter<T> {
+    /// Write an event into the slot.
+    fn write(&self, event: T) {
+        // Ignore if the sink is closed.
+        if !self.inner.is_open.load(Ordering::Relaxed) {
+            return;
+        }
+
+        // Why do we just use `try_lock` and abandon if the lock is taken? The
+        // reason is that (i) the reader is never supposed to access the slot
+        // when the simulation runs and (ii) as a rule the simulator does not
+        // warrant fairness when concurrently writing to an input. Therefore, if
+        // the mutex is already locked when this writer attempts to lock it, it
+        // means another writer is concurrently writing an event, and that event
+        // is just as legitimate as ours so there is not need to overwrite it.
+        match self.inner.slot.try_lock() {
+            TryLockResult::Ok(mut v) => *v = Some(event),
+            TryLockResult::Err(TryLockError::WouldBlock) => {}
+            TryLockResult::Err(TryLockError::Poisoned(_)) => panic!(),
+        }
+    }
+}
+
+impl<T> Clone for EventSlotWriter<T> {
+    fn clone(&self) -> Self {
+        Self {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl<T> fmt::Debug for EventSlotWriter<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("EventStreamWriter").finish_non_exhaustive()
+    }
+}

nexosim/src/ports/source.rs

@@ -0,0 +1,343 @@
+mod broadcaster;
+mod sender;
+
+use std::fmt;
+use std::sync::Arc;
+use std::time::Duration;
+
+use crate::model::Model;
+use crate::ports::InputFn;
+use crate::simulation::{
+    Action, ActionKey, Address, KeyedOnceAction, KeyedPeriodicAction, OnceAction, PeriodicAction,
+};
+use crate::util::slot;
+use crate::util::unwrap_or_throw::UnwrapOrThrow;
+
+use broadcaster::{EventBroadcaster, QueryBroadcaster, ReplyIterator};
+use sender::{
+    FilterMapInputSender, FilterMapReplierSender, InputSender, MapInputSender, MapReplierSender,
+    ReplierSender,
+};
+
+use super::ReplierFn;
+
+/// An event source port.
+///
+/// The `EventSource` port is similar to an [`Output`](crate::ports::Output)
+/// port in that it can send events to connected input ports. It is not meant,
+/// however, to be instantiated as a member of a model, but rather as a
+/// simulation control endpoint instantiated during bench assembly.
+pub struct EventSource<T: Clone + Send + 'static> {
+    broadcaster: EventBroadcaster<T>,
+}
+
+impl<T: Clone + Send + 'static> EventSource<T> {
+    /// Creates a disconnected `EventSource` port.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Adds a connection to an input port of the model specified by the
+    /// address.
+    ///
+    /// The input port must be an asynchronous method of a model of type `M`
+    /// taking as argument a value of type `T` plus, optionally, a scheduler
+    /// reference.
+    pub fn connect<M, F, S>(&mut self, input: F, address: impl Into<Address<M>>)
+    where
+        M: Model,
+        F: for<'a> InputFn<'a, M, T, S> + Clone + Sync,
+        S: Send + Sync + 'static,
+    {
+        let sender = Box::new(InputSender::new(input, address.into().0));
+        self.broadcaster.add(sender);
+    }
+
+    /// Adds an auto-converting connection to an input port of the model
+    /// specified by the address.
+    ///
+    /// Events are mapped to another type using the closure provided in
+    /// argument.
+    ///
+    /// The input port must be an asynchronous method of a model of type `M`
+    /// taking as argument a value of the type returned by the mapping closure
+    /// plus, optionally, a context reference.
+    pub fn map_connect<M, C, F, U, S>(&mut self, map: C, input: F, address: impl Into<Address<M>>)
+    where
+        M: Model,
+        C: for<'a> Fn(&'a T) -> U + Send + Sync + 'static,
+        F: for<'a> InputFn<'a, M, U, S> + Sync + Clone,
+        U: Send + 'static,
+        S: Send + Sync + 'static,
+    {
+        let sender = Box::new(MapInputSender::new(map, input, address.into().0));
+        self.broadcaster.add(sender);
+    }
+
+    /// Adds an auto-converting, filtered connection to an input port of the
+    /// model specified by the address.
+    ///
+    /// Events are mapped to another type using the closure provided in
+    /// argument, or ignored if the closure returns `None`.
+    ///
+    /// The input port must be an asynchronous method of a model of type `M`
+    /// taking as argument a value of the type returned by the mapping closure
+    /// plus, optionally, a context reference.
+    pub fn filter_map_connect<M, C, F, U, S>(
+        &mut self,
+        map: C,
+        input: F,
+        address: impl Into<Address<M>>,
+    ) where
+        M: Model,
+        C: for<'a> Fn(&'a T) -> Option<U> + Send + Sync + 'static,
+        F: for<'a> InputFn<'a, M, U, S> + Clone + Sync,
+        U: Send + 'static,
+        S: Send + Sync + 'static,
+    {
+        let sender = Box::new(FilterMapInputSender::new(map, input, address.into().0));
+        self.broadcaster.add(sender);
+    }
+
+    /// Returns an action which, when processed, broadcasts an event to all
+    /// connected input ports.
+    pub fn event(&self, arg: T) -> Action {
+        let fut = self.broadcaster.broadcast(arg);
+        let fut = async {
+            fut.await.unwrap_or_throw();
+        };
+
+        Action::new(OnceAction::new(fut))
+    }
+
+    /// Returns a cancellable action and a cancellation key; when processed, the
+    /// action broadcasts an event to all connected input ports.
+    pub fn keyed_event(&self, arg: T) -> (Action, ActionKey) {
+        let action_key = ActionKey::new();
+        let fut = self.broadcaster.broadcast(arg);
+
+        let action = Action::new(KeyedOnceAction::new(
+            // Cancellation is ignored once the action is already spawned on the
+            // executor. This means the action cannot be cancelled once the
+            // simulation step targeted by the action is running, but since an
+            // event source is meant to be used outside the simulator, this
+            // shouldn't be an issue in practice.
+            |_| async {
+                fut.await.unwrap_or_throw();
+            },
+            action_key.clone(),
+        ));
+
+        (action, action_key)
+    }
+
+    /// Returns a periodically recurring action which, when processed,
+    /// broadcasts an event to all connected input ports.
+    pub fn periodic_event(self: &Arc<Self>, period: Duration, arg: T) -> Action {
+        let source = self.clone();
+
+        Action::new(PeriodicAction::new(
+            || async move {
+                let fut = source.broadcaster.broadcast(arg);
+                fut.await.unwrap_or_throw();
+            },
+            period,
+        ))
+    }
+
+    /// Returns a cancellable, periodically recurring action and a cancellation
+    /// key; when processed, the action broadcasts an event to all connected
+    /// input ports.
+    pub fn keyed_periodic_event(self: &Arc<Self>, period: Duration, arg: T) -> (Action, ActionKey) {
+        let action_key = ActionKey::new();
+        let source = self.clone();
+
+        let action = Action::new(KeyedPeriodicAction::new(
+            // Cancellation is ignored once the action is already spawned on the
+            // executor. This means the action cannot be cancelled while the
+            // simulation is running, but since an event source is meant to be
+            // used outside the simulator, this shouldn't be an issue in
+            // practice.
+            |_| async move {
+                let fut = source.broadcaster.broadcast(arg);
+                fut.await.unwrap_or_throw();
+            },
+            period,
+            action_key.clone(),
+        ));
+
+        (action, action_key)
+    }
+}
+
+impl<T: Clone + Send + 'static> Default for EventSource<T> {
+    fn default() -> Self {
+        Self {
+            broadcaster: EventBroadcaster::default(),
+        }
+    }
+}
+
+impl<T: Clone + Send + 'static> fmt::Debug for EventSource<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "Event source ({} connected ports)",
+            self.broadcaster.len()
+        )
+    }
+}
+
+/// A query source port.
+///
+/// The `QuerySource` port is similar to an
+/// [`Requestor`](crate::ports::Requestor) port in that it can send requests to
+/// connected replier ports and receive replies. It is not meant, however, to be
+/// instantiated as a member of a model, but rather as a simulation monitoring
+/// endpoint instantiated during bench assembly.
+pub struct QuerySource<T: Clone + Send + 'static, R: Send + 'static> {
+    broadcaster: QueryBroadcaster<T, R>,
+}
+
+impl<T: Clone + Send + 'static, R: Send + 'static> QuerySource<T, R> {
+    /// Creates a disconnected `EventSource` port.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Adds a connection to a replier port of the model specified by the
+    /// address.
+    ///
+    /// The replier port must be an asynchronous method of a model of type `M`
+    /// returning a value of type `R` and taking as argument a value of type `T`
+    /// plus, optionally, a context reference.
+    pub fn connect<M, F, S>(&mut self, replier: F, address: impl Into<Address<M>>)
+    where
+        M: Model,
+        F: for<'a> ReplierFn<'a, M, T, R, S> + Clone + Sync,
+        S: Send + Sync + 'static,
+    {
+        let sender = Box::new(ReplierSender::new(replier, address.into().0));
+        self.broadcaster.add(sender);
+    }
+
+    /// Adds an auto-converting connection to a replier port of the model
+    /// specified by the address.
+    ///
+    /// Queries and replies are mapped to other types using the closures
+    /// provided in argument.
+    ///
+    /// The replier port must be an asynchronous method of a model of type `M`
+    /// returning a value of the type returned by the reply mapping closure and
+    /// taking as argument a value of the type returned by the query mapping
+    /// closure plus, optionally, a context reference.
+    pub fn map_connect<M, C, D, F, U, Q, S>(
+        &mut self,
+        query_map: C,
+        reply_map: D,
+        replier: F,
+        address: impl Into<Address<M>>,
+    ) where
+        M: Model,
+        C: for<'a> Fn(&'a T) -> U + Send + Sync + 'static,
+        D: Fn(Q) -> R + Send + Sync + 'static,
+        F: for<'a> ReplierFn<'a, M, U, Q, S> + Clone + Sync,
+        U: Send + 'static,
+        Q: Send + 'static,
+        S: Send + Sync + 'static,
+    {
+        let sender = Box::new(MapReplierSender::new(
+            query_map,
+            reply_map,
+            replier,
+            address.into().0,
+        ));
+        self.broadcaster.add(sender);
+    }
+
+    /// Adds an auto-converting, filtered connection to a replier port of the
+    /// model specified by the address.
+    ///
+    /// Queries and replies are mapped to other types using the closures
+    /// provided in argument, or ignored if the query closure returns `None`.
+    ///
+    /// The replier port must be an asynchronous method of a model of type `M`
+    /// returning a value of the type returned by the reply mapping closure and
+    /// taking as argument a value of the type returned by the query mapping
+    /// closure plus, optionally, a context reference.
+    pub fn filter_map_connect<M, C, D, F, U, Q, S>(
+        &mut self,
+        query_filter_map: C,
+        reply_map: D,
+        replier: F,
+        address: impl Into<Address<M>>,
+    ) where
+        M: Model,
+        C: for<'a> Fn(&'a T) -> Option<U> + Send + Sync + 'static,
+        D: Fn(Q) -> R + Send + Sync + 'static,
+        F: for<'a> ReplierFn<'a, M, U, Q, S> + Clone + Sync,
+        U: Send + 'static,
+        Q: Send + 'static,
+        S: Send + Sync + 'static,
+    {
+        let sender = Box::new(FilterMapReplierSender::new(
+            query_filter_map,
+            reply_map,
+            replier,
+            address.into().0,
+        ));
+        self.broadcaster.add(sender);
+    }
+
+    /// Returns an action which, when processed, broadcasts a query to all
+    /// connected replier ports.
+    pub fn query(&self, arg: T) -> (Action, ReplyReceiver<R>) {
+        let (writer, reader) = slot::slot();
+        let fut = self.broadcaster.broadcast(arg);
+        let fut = async move {
+            let replies = fut.await.unwrap_or_throw();
+            let _ = writer.write(replies);
+        };
+
+        let action = Action::new(OnceAction::new(fut));
+
+        (action, ReplyReceiver::<R>(reader))
+    }
+}
+
+impl<T: Clone + Send + 'static, R: Send + 'static> Default for QuerySource<T, R> {
+    fn default() -> Self {
+        Self {
+            broadcaster: QueryBroadcaster::default(),
+        }
+    }
+}
+
+impl<T: Clone + Send + 'static, R: Send + 'static> fmt::Debug for QuerySource<T, R> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "Query source ({} connected ports)",
+            self.broadcaster.len()
+        )
+    }
+}
+
+/// A receiver for all replies collected from a single query broadcast.
+pub struct ReplyReceiver<R>(slot::SlotReader<ReplyIterator<R>>);
+
+impl<R> ReplyReceiver<R> {
+    /// Returns all replies to a query.
+    ///
+    /// Returns `None` if the replies are not yet available or if they were
+    /// already taken in a previous call to `take`.
+    pub fn take(&mut self) -> Option<impl Iterator<Item = R>> {
+        self.0.try_read().ok()
+    }
+}
+
+impl<R> fmt::Debug for ReplyReceiver<R> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "Replies")
+    }
+}

nexosim/src/ports/source/broadcaster.rs

@@ -0,0 +1,903 @@
+use std::future::Future;
+use std::mem;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::vec;
+
+use pin_project::pin_project;
+
+use diatomic_waker::WakeSink;
+
+use super::sender::{Sender, SenderFuture};
+
+use crate::channel::SendError;
+use crate::util::task_set::TaskSet;
+
+/// An object that can efficiently broadcast messages to several addresses.
+///
+/// This is very similar to `output::broadcaster::BroadcasterInner`, but
+/// generates owned futures instead.
+///
+/// This object maintains a list of senders associated to each target address.
+/// When a message is broadcast, the sender futures are awaited in parallel.
+/// This is somewhat similar to what `FuturesOrdered` in the `futures` crate
+/// does, but the outputs of all sender futures are returned all at once rather
+/// than with an asynchronous iterator (a.k.a. async stream).
+pub(super) struct BroadcasterInner<T: Clone, R> {
+    /// The list of senders with their associated line identifier.
+    senders: Vec<Box<dyn Sender<T, R>>>,
+}
+
+impl<T: Clone, R> BroadcasterInner<T, R> {
+    /// Adds a new sender associated to the specified identifier.
+    ///
+    /// # Panics
+    ///
+    /// This method will panic if the total count of senders would reach
+    /// `u32::MAX - 1` due to limitations inherent to the task set
+    /// implementation.
+    pub(super) fn add(&mut self, sender: Box<dyn Sender<T, R>>) {
+        assert!(self.senders.len() < (u32::MAX as usize - 2));
+        self.senders.push(sender);
+    }
+
+    /// Returns the number of connected senders.
+    pub(super) fn len(&self) -> usize {
+        self.senders.len()
+    }
+
+    /// Return a list of futures broadcasting an event or query to multiple
+    /// addresses.
+    fn futures(&self, arg: T) -> Vec<SenderFutureState<R>> {
+        let mut future_states = Vec::new();
+
+        // Broadcast the message and collect all futures.
+        let mut iter = self.senders.iter();
+        while let Some(sender) = iter.next() {
+            // Move the argument for the last future to avoid undue cloning.
+            if iter.len() == 0 {
+                if let Some(fut) = sender.send_owned(arg) {
+                    future_states.push(SenderFutureState::Pending(fut));
+                }
+                break;
+            }
+            if let Some(fut) = sender.send(&arg) {
+                future_states.push(SenderFutureState::Pending(fut));
+            }
+        }
+
+        future_states
+    }
+}
+
+impl<T: Clone, R> Default for BroadcasterInner<T, R> {
+    fn default() -> Self {
+        Self {
+            senders: Vec::new(),
+        }
+    }
+}
+
+/// An object that can efficiently broadcast events to several input ports.
+///
+/// This is very similar to `output::broadcaster::EventBroadcaster`, but
+/// generates owned futures instead.
+///
+/// See `BroadcasterInner` for implementation details.
+pub(super) struct EventBroadcaster<T: Clone> {
+    /// The broadcaster core object.
+    inner: BroadcasterInner<T, ()>,
+}
+
+impl<T: Clone + Send> EventBroadcaster<T> {
+    /// Adds a new sender associated to the specified identifier.
+    ///
+    /// # Panics
+    ///
+    /// This method will panic if the total count of senders would reach
+    /// `u32::MAX - 1` due to limitations inherent to the task set
+    /// implementation.
+    pub(super) fn add(&mut self, sender: Box<dyn Sender<T, ()>>) {
+        self.inner.add(sender);
+    }
+
+    /// Returns the number of connected senders.
+    pub(super) fn len(&self) -> usize {
+        self.inner.len()
+    }
+
+    /// Broadcasts an event to all addresses.
+    pub(super) fn broadcast(&self, arg: T) -> impl Future<Output = Result<(), SendError>> + Send {
+        enum Fut<F1, F2> {
+            Empty,
+            Single(F1),
+            Multiple(F2),
+        }
+
+        let fut = match self.inner.senders.as_slice() {
+            // No sender.
+            [] => Fut::Empty,
+            // One sender at most.
+            [sender] => Fut::Single(sender.send_owned(arg)),
+            // Possibly multiple senders.
+            _ => Fut::Multiple(self.inner.futures(arg)),
+        };
+
+        async {
+            match fut {
+                // No sender.
+                Fut::Empty | Fut::Single(None) => Ok(()),
+
+                Fut::Single(Some(fut)) => fut.await,
+
+                Fut::Multiple(mut futures) => match futures.as_mut_slice() {
+                    // No sender.
+                    [] => Ok(()),
+                    // One sender.
+                    [SenderFutureState::Pending(fut)] => fut.await,
+                    // Multiple senders.
+                    _ => BroadcastFuture::new(futures).await.map(|_| ()),
+                },
+            }
+        }
+    }
+}
+
+impl<T: Clone> Default for EventBroadcaster<T> {
+    fn default() -> Self {
+        Self {
+            inner: BroadcasterInner::default(),
+        }
+    }
+}
+
+/// An object that can efficiently broadcast queries to several replier ports.
+///
+/// This is very similar to `output::broadcaster::QueryBroadcaster`, but
+/// generates owned futures instead.
+///
+/// See `BroadcasterInner` for implementation details.
+pub(super) struct QueryBroadcaster<T: Clone, R> {
+    /// The broadcaster core object.
+    inner: BroadcasterInner<T, R>,
+}
+
+impl<T: Clone + Send, R: Send> QueryBroadcaster<T, R> {
+    /// Adds a new sender associated to the specified identifier.
+    ///
+    /// # Panics
+    ///
+    /// This method will panic if the total count of senders would reach
+    /// `u32::MAX - 1` due to limitations inherent to the task set
+    /// implementation.
+    pub(super) fn add(&mut self, sender: Box<dyn Sender<T, R>>) {
+        self.inner.add(sender);
+    }
+
+    /// Returns the number of connected senders.
+    pub(super) fn len(&self) -> usize {
+        self.inner.len()
+    }
+
+    /// Broadcasts an event to all addresses.
+    pub(super) fn broadcast(
+        &self,
+        arg: T,
+    ) -> impl Future<Output = Result<ReplyIterator<R>, SendError>> + Send {
+        enum Fut<F1, F2> {
+            Empty,
+            Single(F1),
+            Multiple(F2),
+        }
+
+        let fut = match self.inner.senders.as_slice() {
+            // No sender.
+            [] => Fut::Empty,
+            // One sender at most.
+            [sender] => Fut::Single(sender.send_owned(arg)),
+            // Possibly multiple senders.
+            _ => Fut::Multiple(self.inner.futures(arg)),
+        };
+
+        async {
+            match fut {
+                // No sender.
+                Fut::Empty | Fut::Single(None) => Ok(ReplyIterator(Vec::new().into_iter())),
+
+                Fut::Single(Some(fut)) => fut
+                    .await
+                    .map(|reply| ReplyIterator(vec![SenderFutureState::Ready(reply)].into_iter())),
+
+                Fut::Multiple(mut futures) => match futures.as_mut_slice() {
+                    // No sender.
+                    [] => Ok(ReplyIterator(Vec::new().into_iter())),
+
+                    // One sender.
+                    [SenderFutureState::Pending(fut)] => fut.await.map(|reply| {
+                        ReplyIterator(vec![SenderFutureState::Ready(reply)].into_iter())
+                    }),
+
+                    // Multiple senders.
+                    _ => BroadcastFuture::new(futures).await,
+                },
+            }
+        }
+    }
+}
+
+impl<T: Clone, R> Default for QueryBroadcaster<T, R> {
+    fn default() -> Self {
+        Self {
+            inner: BroadcasterInner::default(),
+        }
+    }
+}
+
+#[pin_project]
+/// A future aggregating the outputs of a collection of sender futures.
+///
+/// The idea is to join all sender futures as efficiently as possible, meaning:
+///
+/// - the sender futures are polled simultaneously rather than waiting for their
+///   completion in a sequential manner,
+/// - the happy path (all futures immediately ready) is very fast.
+pub(super) struct BroadcastFuture<R> {
+    // Thread-safe waker handle.
+    wake_sink: WakeSink,
+    // Tasks associated to the sender futures.
+    task_set: TaskSet,
+    // List of all sender futures or their outputs.
+    future_states: Vec<SenderFutureState<R>>,
+    // The total count of futures that have not yet been polled to completion.
+    pending_futures_count: usize,
+    // State of completion of the future.
+    state: FutureState,
+}
+
+impl<R> BroadcastFuture<R> {
+    /// Creates a new `BroadcastFuture`.
+    fn new(future_states: Vec<SenderFutureState<R>>) -> Self {
+        let wake_sink = WakeSink::new();
+        let wake_src = wake_sink.source();
+        let pending_futures_count = future_states.len();
+
+        BroadcastFuture {
+            wake_sink,
+            task_set: TaskSet::with_len(wake_src, pending_futures_count),
+            future_states,
+            pending_futures_count,
+            state: FutureState::Uninit,
+        }
+    }
+}
+
+impl<R> Future for BroadcastFuture<R> {
+    type Output = Result<ReplyIterator<R>, SendError>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = &mut *self;
+
+        assert_ne!(this.state, FutureState::Completed);
+
+        // Poll all sender futures once if this is the first time the broadcast
+        // future is polled.
+        if this.state == FutureState::Uninit {
+            for task_idx in 0..this.future_states.len() {
+                if let SenderFutureState::Pending(future) = &mut this.future_states[task_idx] {
+                    let task_waker_ref = this.task_set.waker_of(task_idx);
+                    let task_cx_ref = &mut Context::from_waker(&task_waker_ref);
+
+                    match future.as_mut().poll(task_cx_ref) {
+                        Poll::Ready(Ok(output)) => {
+                            this.future_states[task_idx] = SenderFutureState::Ready(output);
+                            this.pending_futures_count -= 1;
+                        }
+                        Poll::Ready(Err(SendError)) => {
+                            this.state = FutureState::Completed;
+
+                            return Poll::Ready(Err(SendError));
+                        }
+                        Poll::Pending => {}
+                    }
+                }
+            }
+
+            if this.pending_futures_count == 0 {
+                this.state = FutureState::Completed;
+                let outputs = mem::take(&mut this.future_states).into_iter();
+
+                return Poll::Ready(Ok(ReplyIterator(outputs)));
+            }
+
+            this.state = FutureState::Pending;
+        }
+
+        // Repeatedly poll the futures of all scheduled tasks until there are no
+        // more scheduled tasks.
+        loop {
+            // No need to register the waker if some tasks have been scheduled.
+            if !this.task_set.has_scheduled() {
+                this.wake_sink.register(cx.waker());
+            }
+
+            // Retrieve the indices of the scheduled tasks if any. If there are
+            // no scheduled tasks, `Poll::Pending` is returned and this future
+            // will be awaken again when enough tasks have been scheduled.
+            //
+            // NOTE: the current implementation requires a notification to be
+            // sent each time a sub-future has made progress. We may try at some
+            // point to benchmark an alternative strategy where a notification
+            // is requested only when all pending sub-futures have made progress,
+            // using `take_scheduled(this.pending_futures_count)`. This would
+            // reduce the cost of context switch but could hurt latency.
+            let scheduled_tasks = match this.task_set.take_scheduled(1) {
+                Some(st) => st,
+                None => return Poll::Pending,
+            };
+
+            for task_idx in scheduled_tasks {
+                if let SenderFutureState::Pending(future) = &mut this.future_states[task_idx] {
+                    let task_waker_ref = this.task_set.waker_of(task_idx);
+                    let task_cx_ref = &mut Context::from_waker(&task_waker_ref);
+
+                    match future.as_mut().poll(task_cx_ref) {
+                        Poll::Ready(Ok(output)) => {
+                            this.future_states[task_idx] = SenderFutureState::Ready(output);
+                            this.pending_futures_count -= 1;
+                        }
+                        Poll::Ready(Err(SendError)) => {
+                            this.state = FutureState::Completed;
+
+                            return Poll::Ready(Err(SendError));
+                        }
+                        Poll::Pending => {}
+                    }
+                }
+            }
+
+            if this.pending_futures_count == 0 {
+                this.state = FutureState::Completed;
+                let outputs = mem::take(&mut this.future_states).into_iter();
+
+                return Poll::Ready(Ok(ReplyIterator(outputs)));
+            }
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+enum FutureState {
+    Uninit,
+    Pending,
+    Completed,
+}
+
+/// The state of a `SenderFuture`.
+enum SenderFutureState<R> {
+    Pending(SenderFuture<R>),
+    Ready(R),
+}
+
+/// An iterator over the replies to a broadcasted request.
+pub(crate) struct ReplyIterator<R>(vec::IntoIter<SenderFutureState<R>>);
+
+impl<R> Iterator for ReplyIterator<R> {
+    type Item = R;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.0.next().map(|state| match state {
+            SenderFutureState::Ready(reply) => reply,
+            _ => panic!("reply missing in replies iterator"),
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.0.size_hint()
+    }
+}
+
+#[cfg(all(test, not(nexosim_loom)))]
+mod tests {
+    use std::sync::atomic::{AtomicUsize, Ordering};
+    use std::sync::Arc;
+    use std::thread;
+
+    use futures_executor::block_on;
+
+    use crate::channel::Receiver;
+
+    use super::super::sender::{
+        FilterMapInputSender, FilterMapReplierSender, InputSender, ReplierSender,
+    };
+    use super::*;
+    use crate::model::{Context, Model};
+
+    struct SumModel {
+        inner: Arc<AtomicUsize>,
+    }
+    impl SumModel {
+        fn new(counter: Arc<AtomicUsize>) -> Self {
+            Self { inner: counter }
+        }
+        async fn increment(&mut self, by: usize) {
+            self.inner.fetch_add(by, Ordering::Relaxed);
+        }
+    }
+    impl Model for SumModel {}
+
+    struct DoubleModel {}
+    impl DoubleModel {
+        fn new() -> Self {
+            Self {}
+        }
+        async fn double(&mut self, value: usize) -> usize {
+            2 * value
+        }
+    }
+    impl Model for DoubleModel {}
+
+    #[test]
+    fn broadcast_event_smoke() {
+        const N_RECV: usize = 4;
+        const MESSAGE: usize = 42;
+
+        let mut mailboxes = Vec::new();
+        let mut broadcaster = EventBroadcaster::default();
+        for _ in 0..N_RECV {
+            let mailbox = Receiver::new(10);
+            let address = mailbox.sender();
+            let sender = Box::new(InputSender::new(SumModel::increment, address));
+
+            broadcaster.add(sender);
+            mailboxes.push(mailbox);
+        }
+
+        let th_broadcast = thread::spawn(move || {
+            block_on(broadcaster.broadcast(MESSAGE)).unwrap();
+        });
+
+        let sum = Arc::new(AtomicUsize::new(0));
+
+        let th_recv: Vec<_> = mailboxes
+            .into_iter()
+            .map(|mut mailbox| {
+                thread::spawn({
+                    let mut sum_model = SumModel::new(sum.clone());
+
+                    move || {
+                        let mut dummy_cx = Context::new_dummy();
+                        block_on(mailbox.recv(&mut sum_model, &mut dummy_cx)).unwrap();
+                    }
+                })
+            })
+            .collect();
+
+        th_broadcast.join().unwrap();
+        for th in th_recv {
+            th.join().unwrap();
+        }
+
+        assert_eq!(sum.load(Ordering::Relaxed), N_RECV * MESSAGE);
+    }
+
+    #[test]
+    fn broadcast_event_filter_map() {
+        const N_RECV: usize = 4;
+        const BROADCAST_ALL: usize = 42; // special ID signaling that the message must reach all receivers.
+
+        let mut mailboxes = Vec::new();
+        let mut broadcaster = EventBroadcaster::default();
+        for id in 0..N_RECV {
+            let mailbox = Receiver::new(10);
+            let address = mailbox.sender();
+            let id_filter_sender = Box::new(FilterMapInputSender::new(
+                move |x: &usize| (*x == id || *x == BROADCAST_ALL).then_some(*x),
+                SumModel::increment,
+                address,
+            ));
+
+            broadcaster.add(id_filter_sender);
+            mailboxes.push(mailbox);
+        }
+
+        let th_broadcast = thread::spawn(move || {
+            block_on(async {
+                // Send messages reaching only one receiver each.
+                for id in 0..N_RECV {
+                    broadcaster.broadcast(id).await.unwrap();
+                }
+
+                // Broadcast the special value to all receivers.
+                broadcaster.broadcast(BROADCAST_ALL).await.unwrap();
+
+                // Send again messages reaching only one receiver each.
+                for id in 0..N_RECV {
+                    broadcaster.broadcast(id).await.unwrap();
+                }
+            })
+        });
+
+        let sum = Arc::new(AtomicUsize::new(0));
+
+        // Spawn all models.
+        let th_recv: Vec<_> = mailboxes
+            .into_iter()
+            .map(|mut mailbox| {
+                thread::spawn({
+                    let mut sum_model = SumModel::new(sum.clone());
+
+                    move || {
+                        let mut dummy_cx = Context::new_dummy();
+                        block_on(async {
+                            mailbox.recv(&mut sum_model, &mut dummy_cx).await.unwrap();
+                            mailbox.recv(&mut sum_model, &mut dummy_cx).await.unwrap();
+                            mailbox.recv(&mut sum_model, &mut dummy_cx).await.unwrap();
+                        });
+                    }
+                })
+            })
+            .collect();
+
+        th_broadcast.join().unwrap();
+        for th in th_recv {
+            th.join().unwrap();
+        }
+
+        assert_eq!(
+            sum.load(Ordering::Relaxed),
+            N_RECV * ((N_RECV - 1) + BROADCAST_ALL) // Twice the sum of all IDs + N_RECV times the special value
+        );
+    }
+
+    #[test]
+    fn broadcast_query_smoke() {
+        const N_RECV: usize = 4;
+        const MESSAGE: usize = 42;
+
+        let mut mailboxes = Vec::new();
+        let mut broadcaster = QueryBroadcaster::default();
+        for _ in 0..N_RECV {
+            let mailbox = Receiver::new(10);
+            let address = mailbox.sender();
+            let sender = Box::new(ReplierSender::new(DoubleModel::double, address));
+
+            broadcaster.add(sender);
+            mailboxes.push(mailbox);
+        }
+
+        let th_broadcast = thread::spawn(move || {
+            let iter = block_on(broadcaster.broadcast(MESSAGE)).unwrap();
+
+            iter.sum::<usize>()
+        });
+
+        let th_recv: Vec<_> = mailboxes
+            .into_iter()
+            .map(|mut mailbox| {
+                thread::spawn({
+                    let mut double_model = DoubleModel::new();
+
+                    move || {
+                        let mut dummy_cx = Context::new_dummy();
+                        block_on(mailbox.recv(&mut double_model, &mut dummy_cx)).unwrap();
+                        thread::sleep(std::time::Duration::from_millis(100));
+                    }
+                })
+            })
+            .collect();
+
+        let sum = th_broadcast.join().unwrap();
+        for th in th_recv {
+            th.join().unwrap();
+        }
+
+        assert_eq!(sum, N_RECV * MESSAGE * 2);
+    }
+
+    #[test]
+    fn broadcast_query_filter_map() {
+        const N_RECV: usize = 4;
+        const BROADCAST_ALL: usize = 42; // special ID signaling that the message must reach all receivers.
+
+        let mut mailboxes = Vec::new();
+        let mut broadcaster = QueryBroadcaster::default();
+        for id in 0..N_RECV {
+            let mailbox = Receiver::new(10);
+            let address = mailbox.sender();
+            let sender = Box::new(FilterMapReplierSender::new(
+                move |x: &usize| (*x == id || *x == BROADCAST_ALL).then_some(*x),
+                |x| 3 * x,
+                DoubleModel::double,
+                address,
+            ));
+
+            broadcaster.add(sender);
+            mailboxes.push(mailbox);
+        }
+
+        let th_broadcast = thread::spawn(move || {
+            block_on(async {
+                let mut sum = 0;
+
+                // Send messages reaching only one receiver each.
+                for id in 0..N_RECV {
+                    sum += broadcaster.broadcast(id).await.unwrap().sum::<usize>();
+                }
+
+                // Broadcast the special value to all receivers.
+                sum += broadcaster
+                    .broadcast(BROADCAST_ALL)
+                    .await
+                    .unwrap()
+                    .sum::<usize>();
+
+                // Send again messages reaching only one receiver each.
+                for id in 0..N_RECV {
+                    sum += broadcaster.broadcast(id).await.unwrap().sum::<usize>();
+                }
+
+                sum
+            })
+        });
+
+        let th_recv: Vec<_> = mailboxes
+            .into_iter()
+            .map(|mut mailbox| {
+                thread::spawn({
+                    let mut double_model = DoubleModel::new();
+
+                    move || {
+                        let mut dummy_cx = Context::new_dummy();
+
+                        block_on(async {
+                            mailbox
+                                .recv(&mut double_model, &mut dummy_cx)
+                                .await
+                                .unwrap();
+                            mailbox
+                                .recv(&mut double_model, &mut dummy_cx)
+                                .await
+                                .unwrap();
+                            mailbox
+                                .recv(&mut double_model, &mut dummy_cx)
+                                .await
+                                .unwrap();
+                        });
+                        thread::sleep(std::time::Duration::from_millis(100));
+                    }
+                })
+            })
+            .collect();
+
+        let sum = th_broadcast.join().unwrap();
+        for th in th_recv {
+            th.join().unwrap();
+        }
+
+        assert_eq!(
+            sum,
+            N_RECV * ((N_RECV - 1) + BROADCAST_ALL) * 2 * 3, // Twice the sum of all IDs + N_RECV times the special value, then doubled and tripled
+        );
+    }
+}
+
+#[cfg(all(test, nexosim_loom))]
+mod tests {
+    use std::sync::Mutex;
+
+    use futures_channel::mpsc;
+    use futures_util::StreamExt;
+
+    use loom::model::Builder;
+    use loom::sync::atomic::{AtomicBool, Ordering};
+    use loom::thread;
+
+    use waker_fn::waker_fn;
+
+    use super::*;
+
+    // An event that may be waken spuriously.
+    struct TestEvent<R> {
+        // The receiver is actually used only once in tests, so it is moved out
+        // of the `Option` on first use.
+        receiver: Mutex<Option<mpsc::UnboundedReceiver<Option<R>>>>,
+    }
+    impl<R: Send + 'static> Sender<(), R> for TestEvent<R> {
+        fn send(
+            &self,
+            _arg: &(),
+        ) -> Option<Pin<Box<dyn Future<Output = Result<R, SendError>> + Send>>> {
+            let receiver = self.receiver.lock().unwrap().take().unwrap();
+
+            Some(Box::pin(async move {
+                let mut stream = Box::pin(receiver.filter_map(|item| async { item }));
+
+                Ok(stream.next().await.unwrap())
+            }))
+        }
+    }
+
+    // An object that can wake a `TestEvent`.
+    #[derive(Clone)]
+    struct TestEventWaker<R> {
+        sender: mpsc::UnboundedSender<Option<R>>,
+    }
+    impl<R> TestEventWaker<R> {
+        fn wake_spurious(&self) {
+            let _ = self.sender.unbounded_send(None);
+        }
+        fn wake_final(&self, value: R) {
+            let _ = self.sender.unbounded_send(Some(value));
+        }
+    }
+
+    fn test_event<R>() -> (TestEvent<R>, TestEventWaker<R>) {
+        let (sender, receiver) = mpsc::unbounded();
+
+        (
+            TestEvent {
+                receiver: Mutex::new(Some(receiver)),
+            },
+            TestEventWaker { sender },
+        )
+    }
+
+    // This tests fails with "Concurrent load and mut accesses" even though the
+    // `task_list` implementation which triggers it does not use any unsafe.
+    // This is most certainly related to this Loom bug:
+    //
+    // https://github.com/tokio-rs/loom/issues/260
+    //
+    // Disabling until the bug is fixed.
+    #[ignore]
+    #[test]
+    fn loom_broadcast_query_basic() {
+        const DEFAULT_PREEMPTION_BOUND: usize = 3;
+
+        let mut builder = Builder::new();
+        if builder.preemption_bound.is_none() {
+            builder.preemption_bound = Some(DEFAULT_PREEMPTION_BOUND);
+        }
+
+        builder.check(move || {
+            let (test_event1, waker1) = test_event::<usize>();
+            let (test_event2, waker2) = test_event::<usize>();
+            let (test_event3, waker3) = test_event::<usize>();
+
+            let mut broadcaster = QueryBroadcaster::default();
+            broadcaster.add(Box::new(test_event1));
+            broadcaster.add(Box::new(test_event2));
+            broadcaster.add(Box::new(test_event3));
+
+            let mut fut = Box::pin(broadcaster.broadcast(()));
+            let is_scheduled = loom::sync::Arc::new(AtomicBool::new(false));
+            let is_scheduled_waker = is_scheduled.clone();
+
+            let waker = waker_fn(move || {
+                // We use swap rather than a plain store to work around this
+                // bug: <https://github.com/tokio-rs/loom/issues/254>
+                is_scheduled_waker.swap(true, Ordering::Release);
+            });
+            let mut cx = Context::from_waker(&waker);
+
+            let th1 = thread::spawn(move || waker1.wake_final(3));
+            let th2 = thread::spawn(move || waker2.wake_final(7));
+            let th3 = thread::spawn(move || waker3.wake_final(42));
+
+            loop {
+                match fut.as_mut().poll(&mut cx) {
+                    Poll::Ready(Ok(mut res)) => {
+                        assert_eq!(res.next(), Some(3));
+                        assert_eq!(res.next(), Some(7));
+                        assert_eq!(res.next(), Some(42));
+                        assert_eq!(res.next(), None);
+
+                        return;
+                    }
+                    Poll::Ready(Err(_)) => panic!("sender error"),
+                    Poll::Pending => {}
+                }
+
+                // If the task has not been scheduled, exit the polling loop.
+                if !is_scheduled.swap(false, Ordering::Acquire) {
+                    break;
+                }
+            }
+
+            th1.join().unwrap();
+            th2.join().unwrap();
+            th3.join().unwrap();
+
+            assert!(is_scheduled.load(Ordering::Acquire));
+
+            match fut.as_mut().poll(&mut cx) {
+                Poll::Ready(Ok(mut res)) => {
+                    assert_eq!(res.next(), Some(3));
+                    assert_eq!(res.next(), Some(7));
+                    assert_eq!(res.next(), Some(42));
+                    assert_eq!(res.next(), None);
+                }
+                Poll::Ready(Err(_)) => panic!("sender error"),
+                Poll::Pending => panic!("the future has not completed"),
+            };
+        });
+    }
+
+    // This tests fails with "Concurrent load and mut accesses" even though the
+    // `task_list` implementation which triggers it does not use any unsafe.
+    // This is most certainly related to this Loom bug:
+    //
+    // https://github.com/tokio-rs/loom/issues/260
+    //
+    // Disabling until the bug is fixed.
+    #[ignore]
+    #[test]
+    fn loom_broadcast_query_spurious() {
+        const DEFAULT_PREEMPTION_BOUND: usize = 3;
+
+        let mut builder = Builder::new();
+        if builder.preemption_bound.is_none() {
+            builder.preemption_bound = Some(DEFAULT_PREEMPTION_BOUND);
+        }
+
+        builder.check(move || {
+            let (test_event1, waker1) = test_event::<usize>();
+            let (test_event2, waker2) = test_event::<usize>();
+
+            let mut broadcaster = QueryBroadcaster::default();
+            broadcaster.add(Box::new(test_event1));
+            broadcaster.add(Box::new(test_event2));
+
+            let mut fut = Box::pin(broadcaster.broadcast(()));
+            let is_scheduled = loom::sync::Arc::new(AtomicBool::new(false));
+            let is_scheduled_waker = is_scheduled.clone();
+
+            let waker = waker_fn(move || {
+                // We use swap rather than a plain store to work around this
+                // bug: <https://github.com/tokio-rs/loom/issues/254>
+                is_scheduled_waker.swap(true, Ordering::Release);
+            });
+            let mut cx = Context::from_waker(&waker);
+
+            let spurious_waker = waker1.clone();
+            let th1 = thread::spawn(move || waker1.wake_final(3));
+            let th2 = thread::spawn(move || waker2.wake_final(7));
+            let th_spurious = thread::spawn(move || spurious_waker.wake_spurious());
+
+            loop {
+                match fut.as_mut().poll(&mut cx) {
+                    Poll::Ready(Ok(mut res)) => {
+                        assert_eq!(res.next(), Some(3));
+                        assert_eq!(res.next(), Some(7));
+                        assert_eq!(res.next(), None);
+
+                        return;
+                    }
+                    Poll::Ready(Err(_)) => panic!("sender error"),
+                    Poll::Pending => {}
+                }
+
+                // If the task has not been scheduled, exit the polling loop.
+                if !is_scheduled.swap(false, Ordering::Acquire) {
+                    break;
+                }
+            }
+
+            th1.join().unwrap();
+            th2.join().unwrap();
+            th_spurious.join().unwrap();
+
+            assert!(is_scheduled.load(Ordering::Acquire));
+
+            match fut.as_mut().poll(&mut cx) {
+                Poll::Ready(Ok(mut res)) => {
+                    assert_eq!(res.next(), Some(3));
+                    assert_eq!(res.next(), Some(7));
+                    assert_eq!(res.next(), None);
+                }
+                Poll::Ready(Err(_)) => panic!("sender error"),
+                Poll::Pending => panic!("the future has not completed"),
+            };
+        });
+    }
+}

nexosim/src/ports/source/sender.rs

@@ -0,0 +1,393 @@
+use std::future::Future;
+use std::marker::PhantomData;
+use std::pin::Pin;
+use std::sync::Arc;
+
+use futures_channel::oneshot;
+use recycle_box::{coerce_box, RecycleBox};
+
+use crate::channel;
+use crate::channel::SendError;
+use crate::model::Model;
+use crate::ports::{InputFn, ReplierFn};
+
+pub(super) type SenderFuture<R> = Pin<Box<dyn Future<Output = Result<R, SendError>> + Send>>;
+
+/// An event or query sender abstracting over the target model and input method.
+pub(super) trait Sender<T, R>: Send + Sync {
+    /// Asynchronously sends a message using a reference to the message.
+    fn send(&self, arg: &T) -> Option<SenderFuture<R>>;
+
+    /// Asynchronously sends an owned message.
+    fn send_owned(&self, arg: T) -> Option<SenderFuture<R>> {
+        self.send(&arg)
+    }
+}
+
+/// An object that can send events to an input port.
+pub(super) struct InputSender<M, F, T, S>
+where
+    M: 'static,
+{
+    func: F,
+    sender: channel::Sender<M>,
+    _phantom_closure: PhantomData<fn(&mut M, T)>,
+    _phantom_closure_marker: PhantomData<S>,
+}
+
+impl<M, F, T, S> InputSender<M, F, T, S>
+where
+    M: 'static,
+{
+    pub(super) fn new(func: F, sender: channel::Sender<M>) -> Self {
+        Self {
+            func,
+            sender,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+impl<M, F, T, S> Sender<T, ()> for InputSender<M, F, T, S>
+where
+    M: Model,
+    F: for<'a> InputFn<'a, M, T, S> + Clone + Sync,
+    T: Clone + Send + 'static,
+    S: Send + Sync,
+{
+    fn send(&self, arg: &T) -> Option<SenderFuture<()>> {
+        self.send_owned(arg.clone())
+    }
+
+    fn send_owned(&self, arg: T) -> Option<SenderFuture<()>> {
+        let func = self.func.clone();
+        let sender = self.sender.clone();
+
+        Some(Box::pin(async move {
+            sender
+                .send(move |model, scheduler, recycle_box| {
+                    let fut = func.call(model, arg, scheduler);
+
+                    coerce_box!(RecycleBox::recycle(recycle_box, fut))
+                })
+                .await
+        }))
+    }
+}
+
+/// An object that can send mapped events to an input port.
+pub(super) struct MapInputSender<M, C, F, T, U, S>
+where
+    M: 'static,
+{
+    map: C,
+    func: F,
+    sender: channel::Sender<M>,
+    _phantom_map: PhantomData<fn(T) -> U>,
+    _phantom_closure: PhantomData<fn(&mut M, T)>,
+    _phantom_closure_marker: PhantomData<S>,
+}
+
+impl<M, C, F, T, U, S> MapInputSender<M, C, F, T, U, S>
+where
+    M: 'static,
+{
+    pub(super) fn new(map: C, func: F, sender: channel::Sender<M>) -> Self {
+        Self {
+            map,
+            func,
+            sender,
+            _phantom_map: PhantomData,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+impl<M, C, F, T, U, S> Sender<T, ()> for MapInputSender<M, C, F, T, U, S>
+where
+    M: Model,
+    C: Fn(&T) -> U + Send + Sync,
+    F: for<'a> InputFn<'a, M, U, S> + Clone + Sync,
+    T: Send + 'static,
+    U: Send + 'static,
+    S: Send + Sync,
+{
+    fn send(&self, arg: &T) -> Option<SenderFuture<()>> {
+        let func = self.func.clone();
+        let arg = (self.map)(arg);
+        let sender = self.sender.clone();
+
+        Some(Box::pin(async move {
+            sender
+                .send(move |model, scheduler, recycle_box| {
+                    let fut = func.call(model, arg, scheduler);
+
+                    coerce_box!(RecycleBox::recycle(recycle_box, fut))
+                })
+                .await
+        }))
+    }
+}
+
+/// An object that can filter and send mapped events to an input port.
+pub(super) struct FilterMapInputSender<M, C, F, T, U, S>
+where
+    M: 'static,
+{
+    filter_map: C,
+    func: F,
+    sender: channel::Sender<M>,
+    _phantom_map: PhantomData<fn(T) -> U>,
+    _phantom_closure: PhantomData<fn(&mut M, T)>,
+    _phantom_closure_marker: PhantomData<S>,
+}
+
+impl<M, C, F, T, U, S> FilterMapInputSender<M, C, F, T, U, S>
+where
+    M: 'static,
+{
+    pub(super) fn new(filter_map: C, func: F, sender: channel::Sender<M>) -> Self {
+        Self {
+            filter_map,
+            func,
+            sender,
+            _phantom_map: PhantomData,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+impl<M, C, F, T, U, S> Sender<T, ()> for FilterMapInputSender<M, C, F, T, U, S>
+where
+    M: Model,
+    C: Fn(&T) -> Option<U> + Send + Sync,
+    F: for<'a> InputFn<'a, M, U, S> + Clone + Sync,
+    T: Send + 'static,
+    U: Send + 'static,
+    S: Send + Sync,
+{
+    fn send(&self, arg: &T) -> Option<SenderFuture<()>> {
+        (self.filter_map)(arg).map(|arg| {
+            let func = self.func.clone();
+            let sender = self.sender.clone();
+
+            Box::pin(async move {
+                sender
+                    .send(move |model, scheduler, recycle_box| {
+                        let fut = func.call(model, arg, scheduler);
+
+                        coerce_box!(RecycleBox::recycle(recycle_box, fut))
+                    })
+                    .await
+            }) as SenderFuture<()>
+        })
+    }
+}
+
+/// An object that can send a request to a replier port and retrieve a response.
+pub(super) struct ReplierSender<M, F, T, R, S>
+where
+    M: 'static,
+{
+    func: F,
+    sender: channel::Sender<M>,
+    _phantom_closure: PhantomData<fn(&mut M, T) -> R>,
+    _phantom_closure_marker: PhantomData<S>,
+}
+
+impl<M, F, T, R, S> ReplierSender<M, F, T, R, S>
+where
+    M: 'static,
+{
+    pub(super) fn new(func: F, sender: channel::Sender<M>) -> Self {
+        Self {
+            func,
+            sender,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+impl<M, F, T, R, S> Sender<T, R> for ReplierSender<M, F, T, R, S>
+where
+    M: Model,
+    F: for<'a> ReplierFn<'a, M, T, R, S> + Clone + Sync,
+    T: Clone + Send + 'static,
+    R: Send + 'static,
+    S: Send + Sync,
+{
+    fn send(&self, arg: &T) -> Option<SenderFuture<R>> {
+        self.send_owned(arg.clone())
+    }
+
+    fn send_owned(&self, arg: T) -> Option<SenderFuture<R>> {
+        let func = self.func.clone();
+        let sender = self.sender.clone();
+        let (reply_sender, reply_receiver) = oneshot::channel();
+
+        Some(Box::pin(async move {
+            sender
+                .send(move |model, scheduler, recycle_box| {
+                    let fut = async move {
+                        let reply = func.call(model, arg, scheduler).await;
+                        let _ = reply_sender.send(reply);
+                    };
+
+                    coerce_box!(RecycleBox::recycle(recycle_box, fut))
+                })
+                .await?;
+
+            reply_receiver.await.map_err(|_| SendError)
+        }))
+    }
+}
+
+/// An object that can send a mapped request to a replier port and retrieve a
+/// mapped response.
+pub(super) struct MapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: 'static,
+{
+    query_map: C,
+    reply_map: Arc<D>,
+    func: F,
+    sender: channel::Sender<M>,
+    _phantom_query_map: PhantomData<fn(T) -> U>,
+    _phantom_reply_map: PhantomData<fn(Q) -> R>,
+    _phantom_closure: PhantomData<fn(&mut M, U) -> Q>,
+    _phantom_closure_marker: PhantomData<S>,
+}
+
+impl<M, C, D, F, T, R, U, Q, S> MapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: 'static,
+{
+    pub(super) fn new(query_map: C, reply_map: D, func: F, sender: channel::Sender<M>) -> Self {
+        Self {
+            query_map,
+            reply_map: Arc::new(reply_map),
+            func,
+            sender,
+            _phantom_query_map: PhantomData,
+            _phantom_reply_map: PhantomData,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+impl<M, C, D, F, T, R, U, Q, S> Sender<T, R> for MapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: Model,
+    C: Fn(&T) -> U + Send + Sync,
+    D: Fn(Q) -> R + Send + Sync + 'static,
+    F: for<'a> ReplierFn<'a, M, U, Q, S> + Clone + Sync,
+    T: Send + 'static,
+    R: Send + 'static,
+    U: Send + 'static,
+    Q: Send + 'static,
+    S: Send + Sync,
+{
+    fn send(&self, arg: &T) -> Option<SenderFuture<R>> {
+        let func = self.func.clone();
+        let arg = (self.query_map)(arg);
+        let sender = self.sender.clone();
+        let reply_map = self.reply_map.clone();
+        let (reply_sender, reply_receiver) = oneshot::channel();
+
+        Some(Box::pin(async move {
+            sender
+                .send(move |model, scheduler, recycle_box| {
+                    let fut = async move {
+                        let reply = func.call(model, arg, scheduler).await;
+                        let _ = reply_sender.send(reply);
+                    };
+
+                    coerce_box!(RecycleBox::recycle(recycle_box, fut))
+                })
+                .await?;
+
+            reply_receiver.await.map_err(|_| SendError).map(&*reply_map)
+        }))
+    }
+}
+
+/// An object that can filter and send a mapped request to a replier port and
+/// retrieve a mapped response.
+pub(super) struct FilterMapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: 'static,
+{
+    query_filter_map: C,
+    reply_map: Arc<D>,
+    func: F,
+    sender: channel::Sender<M>,
+    _phantom_query_map: PhantomData<fn(T) -> Option<U>>,
+    _phantom_reply_map: PhantomData<fn(Q) -> R>,
+    _phantom_closure: PhantomData<fn(&mut M, U) -> Q>,
+    _phantom_closure_marker: PhantomData<S>,
+}
+
+impl<M, C, D, F, T, R, U, Q, S> FilterMapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: 'static,
+{
+    pub(super) fn new(
+        query_filter_map: C,
+        reply_map: D,
+        func: F,
+        sender: channel::Sender<M>,
+    ) -> Self {
+        Self {
+            query_filter_map,
+            reply_map: Arc::new(reply_map),
+            func,
+            sender,
+            _phantom_query_map: PhantomData,
+            _phantom_reply_map: PhantomData,
+            _phantom_closure: PhantomData,
+            _phantom_closure_marker: PhantomData,
+        }
+    }
+}
+
+impl<M, C, D, F, T, R, U, Q, S> Sender<T, R> for FilterMapReplierSender<M, C, D, F, T, R, U, Q, S>
+where
+    M: Model,
+    C: Fn(&T) -> Option<U> + Send + Sync,
+    D: Fn(Q) -> R + Send + Sync + 'static,
+    F: for<'a> ReplierFn<'a, M, U, Q, S> + Clone + Sync,
+    T: Send + 'static,
+    R: Send + 'static,
+    U: Send + 'static,
+    Q: Send + 'static,
+    S: Send + Sync,
+{
+    fn send(&self, arg: &T) -> Option<SenderFuture<R>> {
+        (self.query_filter_map)(arg).map(|arg| {
+            let func = self.func.clone();
+            let sender = self.sender.clone();
+            let reply_map = self.reply_map.clone();
+            let (reply_sender, reply_receiver) = oneshot::channel();
+
+            Box::pin(async move {
+                sender
+                    .send(move |model, scheduler, recycle_box| {
+                        let fut = async move {
+                            let reply = func.call(model, arg, scheduler).await;
+                            let _ = reply_sender.send(reply);
+                        };
+
+                        coerce_box!(RecycleBox::recycle(recycle_box, fut))
+                    })
+                    .await?;
+
+                reply_receiver.await.map_err(|_| SendError).map(&*reply_map)
+            }) as SenderFuture<R>
+        })
+    }
+}

nexosim/src/registry.rs

@@ -0,0 +1,75 @@
+//! Registry for sinks and sources.
+//!
+//! This module provides the `EndpointRegistry` object which associates each
+//! event sink, event source and query source in a simulation bench to a unique
+//! name.
+
+mod event_sink_registry;
+mod event_source_registry;
+mod query_source_registry;
+
+use serde::{de::DeserializeOwned, ser::Serialize};
+
+use crate::ports::{EventSinkStream, EventSource, QuerySource};
+
+pub(crate) use event_sink_registry::EventSinkRegistry;
+pub(crate) use event_source_registry::EventSourceRegistry;
+pub(crate) use query_source_registry::QuerySourceRegistry;
+
+/// A registry that holds the sources and sinks of a simulation bench.
+#[derive(Default, Debug)]
+pub struct EndpointRegistry {
+    pub(crate) event_sink_registry: EventSinkRegistry,
+    pub(crate) event_source_registry: EventSourceRegistry,
+    pub(crate) query_source_registry: QuerySourceRegistry,
+}
+
+impl EndpointRegistry {
+    /// Creates a new, empty registry.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Adds an event source to the registry.
+    ///
+    /// If the specified name is already in use for another event source, the source
+    /// provided as argument is returned in the error.
+    pub fn add_event_source<T>(
+        &mut self,
+        source: EventSource<T>,
+        name: impl Into<String>,
+    ) -> Result<(), EventSource<T>>
+    where
+        T: DeserializeOwned + Clone + Send + 'static,
+    {
+        self.event_source_registry.add(source, name)
+    }
+
+    /// Adds a query source to the registry.
+    ///
+    /// If the specified name is already in use for another query source, the
+    /// source provided as argument is returned in the error.
+    pub fn add_query_source<T, R>(
+        &mut self,
+        source: QuerySource<T, R>,
+        name: impl Into<String>,
+    ) -> Result<(), QuerySource<T, R>>
+    where
+        T: DeserializeOwned + Clone + Send + 'static,
+        R: Serialize + Send + 'static,
+    {
+        self.query_source_registry.add(source, name)
+    }
+
+    /// Adds an event sink to the registry.
+    ///
+    /// If the specified name is already in use for another event sink, the
+    /// event sink provided as argument is returned in the error.
+    pub fn add_event_sink<S>(&mut self, sink: S, name: impl Into<String>) -> Result<(), S>
+    where
+        S: EventSinkStream + Send + 'static,
+        S::Item: Serialize,
+    {
+        self.event_sink_registry.add(sink, name)
+    }
+}

nexosim/src/registry/event_sink_registry.rs

@@ -0,0 +1,93 @@
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+use std::fmt;
+
+use ciborium;
+use serde::Serialize;
+
+use crate::ports::EventSinkStream;
+
+type SerializationError = ciborium::ser::Error<std::io::Error>;
+
+/// A registry that holds all sinks meant to be accessed through remote
+/// procedure calls.
+#[derive(Default)]
+pub(crate) struct EventSinkRegistry(HashMap<String, Box<dyn EventSinkStreamAny>>);
+
+impl EventSinkRegistry {
+    /// Adds a sink to the registry.
+    ///
+    /// If the specified name is already in use for another sink, the sink
+    /// provided as argument is returned in the error.
+    pub(crate) fn add<S>(&mut self, sink: S, name: impl Into<String>) -> Result<(), S>
+    where
+        S: EventSinkStream + Send + 'static,
+        S::Item: Serialize,
+    {
+        match self.0.entry(name.into()) {
+            Entry::Vacant(s) => {
+                s.insert(Box::new(sink));
+
+                Ok(())
+            }
+            Entry::Occupied(_) => Err(sink),
+        }
+    }
+
+    /// Returns a mutable reference to the specified sink if it is in the
+    /// registry.
+    pub(crate) fn get_mut(&mut self, name: &str) -> Option<&mut dyn EventSinkStreamAny> {
+        self.0.get_mut(name).map(|s| s.as_mut())
+    }
+}
+
+impl fmt::Debug for EventSinkRegistry {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "EventSinkRegistry ({} sinks)", self.0.len())
+    }
+}
+
+/// A type-erased `EventSinkStream`.
+pub(crate) trait EventSinkStreamAny: Send + 'static {
+    /// Human-readable name of the event type, as returned by
+    /// `any::type_name`.
+    fn event_type_name(&self) -> &'static str;
+
+    /// Starts or resumes the collection of new events.
+    fn open(&mut self);
+
+    /// Pauses the collection of new events.
+    fn close(&mut self);
+
+    /// Encode and collect all events in a vector.
+    fn collect(&mut self) -> Result<Vec<Vec<u8>>, SerializationError>;
+}
+
+impl<E> EventSinkStreamAny for E
+where
+    E: EventSinkStream + Send + 'static,
+    E::Item: Serialize,
+{
+    fn event_type_name(&self) -> &'static str {
+        std::any::type_name::<E::Item>()
+    }
+
+    fn open(&mut self) {
+        self.open();
+    }
+
+    fn close(&mut self) {
+        self.close();
+    }
+
+    fn collect(&mut self) -> Result<Vec<Vec<u8>>, SerializationError> {
+        self.__try_fold(Vec::new(), |mut encoded_events, event| {
+            let mut buffer = Vec::new();
+            ciborium::into_writer(&event, &mut buffer).map(|_| {
+                encoded_events.push(buffer);
+
+                encoded_events
+            })
+        })
+    }
+}

nexosim/src/registry/event_source_registry.rs

@@ -0,0 +1,130 @@
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+use std::fmt;
+use std::sync::Arc;
+use std::time::Duration;
+
+use ciborium;
+use serde::de::DeserializeOwned;
+
+use crate::ports::EventSource;
+use crate::simulation::{Action, ActionKey};
+
+type DeserializationError = ciborium::de::Error<std::io::Error>;
+
+/// A registry that holds all sources and sinks meant to be accessed through
+/// remote procedure calls.
+#[derive(Default)]
+pub(crate) struct EventSourceRegistry(HashMap<String, Box<dyn EventSourceAny>>);
+
+impl EventSourceRegistry {
+    /// Adds an event source to the registry.
+    ///
+    /// If the specified name is already in use for another event source, the source
+    /// provided as argument is returned in the error.
+    pub(crate) fn add<T>(
+        &mut self,
+        source: EventSource<T>,
+        name: impl Into<String>,
+    ) -> Result<(), EventSource<T>>
+    where
+        T: DeserializeOwned + Clone + Send + 'static,
+    {
+        match self.0.entry(name.into()) {
+            Entry::Vacant(s) => {
+                s.insert(Box::new(Arc::new(source)));
+
+                Ok(())
+            }
+            Entry::Occupied(_) => Err(source),
+        }
+    }
+
+    /// Returns a mutable reference to the specified event source if it is in
+    /// the registry.
+    pub(crate) fn get(&self, name: &str) -> Option<&dyn EventSourceAny> {
+        self.0.get(name).map(|s| s.as_ref())
+    }
+}
+
+impl fmt::Debug for EventSourceRegistry {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "EventSourceRegistry ({} sources)", self.0.len())
+    }
+}
+
+/// A type-erased `EventSource` that operates on CBOR-encoded serialized events.
+pub(crate) trait EventSourceAny: Send + Sync + 'static {
+    /// Returns an action which, when processed, broadcasts an event to all
+    /// connected input ports.
+    ///
+    /// The argument is expected to conform to the serde CBOR encoding.
+    fn event(&self, serialized_arg: &[u8]) -> Result<Action, DeserializationError>;
+
+    /// Returns a cancellable action and a cancellation key; when processed, the
+    /// action broadcasts an event to all connected input ports.
+    ///
+    /// The argument is expected to conform to the serde CBOR encoding.
+    fn keyed_event(
+        &self,
+        serialized_arg: &[u8],
+    ) -> Result<(Action, ActionKey), DeserializationError>;
+
+    /// Returns a periodically recurring action which, when processed,
+    /// broadcasts an event to all connected input ports.
+    ///
+    /// The argument is expected to conform to the serde CBOR encoding.
+    fn periodic_event(
+        &self,
+        period: Duration,
+        serialized_arg: &[u8],
+    ) -> Result<Action, DeserializationError>;
+
+    /// Returns a cancellable, periodically recurring action and a cancellation
+    /// key; when processed, the action broadcasts an event to all connected
+    /// input ports.
+    ///
+    /// The argument is expected to conform to the serde CBOR encoding.
+    fn keyed_periodic_event(
+        &self,
+        period: Duration,
+        serialized_arg: &[u8],
+    ) -> Result<(Action, ActionKey), DeserializationError>;
+
+    /// Human-readable name of the event type, as returned by
+    /// `any::type_name`.
+    fn event_type_name(&self) -> &'static str;
+}
+
+impl<T> EventSourceAny for Arc<EventSource<T>>
+where
+    T: DeserializeOwned + Clone + Send + 'static,
+{
+    fn event(&self, serialized_arg: &[u8]) -> Result<Action, DeserializationError> {
+        ciborium::from_reader(serialized_arg).map(|arg| EventSource::event(self, arg))
+    }
+    fn keyed_event(
+        &self,
+        serialized_arg: &[u8],
+    ) -> Result<(Action, ActionKey), DeserializationError> {
+        ciborium::from_reader(serialized_arg).map(|arg| EventSource::keyed_event(self, arg))
+    }
+    fn periodic_event(
+        &self,
+        period: Duration,
+        serialized_arg: &[u8],
+    ) -> Result<Action, DeserializationError> {
+        ciborium::from_reader(serialized_arg)
+            .map(|arg| EventSource::periodic_event(self, period, arg))
+    }
+    fn keyed_periodic_event(
+        &self,
+        period: Duration,
+        serialized_arg: &[u8],
+    ) -> Result<(Action, ActionKey), DeserializationError> {
+        ciborium::from_reader(serialized_arg).map(|arg| self.keyed_periodic_event(period, arg))
+    }
+    fn event_type_name(&self) -> &'static str {
+        std::any::type_name::<T>()
+    }
+}

nexosim/src/registry/query_source_registry.rs

@@ -0,0 +1,128 @@
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+use std::fmt;
+
+use ciborium;
+use serde::de::DeserializeOwned;
+use serde::Serialize;
+
+use crate::ports::{QuerySource, ReplyReceiver};
+use crate::simulation::Action;
+
+type DeserializationError = ciborium::de::Error<std::io::Error>;
+type SerializationError = ciborium::ser::Error<std::io::Error>;
+
+/// A registry that holds all sources and sinks meant to be accessed through
+/// remote procedure calls.
+#[derive(Default)]
+pub(crate) struct QuerySourceRegistry(HashMap<String, Box<dyn QuerySourceAny>>);
+
+impl QuerySourceRegistry {
+    /// Adds a query source to the registry.
+    ///
+    /// If the specified name is already in use for another query source, the
+    /// source provided as argument is returned in the error.
+    pub(crate) fn add<T, R>(
+        &mut self,
+        source: QuerySource<T, R>,
+        name: impl Into<String>,
+    ) -> Result<(), QuerySource<T, R>>
+    where
+        T: DeserializeOwned + Clone + Send + 'static,
+        R: Serialize + Send + 'static,
+    {
+        match self.0.entry(name.into()) {
+            Entry::Vacant(s) => {
+                s.insert(Box::new(source));
+
+                Ok(())
+            }
+            Entry::Occupied(_) => Err(source),
+        }
+    }
+
+    /// Returns a mutable reference to the specified query source if it is in
+    /// the registry.
+    pub(crate) fn get(&self, name: &str) -> Option<&dyn QuerySourceAny> {
+        self.0.get(name).map(|s| s.as_ref())
+    }
+}
+
+impl fmt::Debug for QuerySourceRegistry {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "QuerySourceRegistry ({} query sources)", self.0.len(),)
+    }
+}
+
+/// A type-erased `QuerySource` that operates on CBOR-encoded serialized queries
+/// and returns CBOR-encoded replies.
+pub(crate) trait QuerySourceAny: Send + Sync + 'static {
+    /// Returns an action which, when processed, broadcasts a query to all
+    /// connected replier ports.
+    ///
+    ///
+    /// The argument is expected to conform to the serde CBOR encoding.
+    fn query(
+        &self,
+        arg: &[u8],
+    ) -> Result<(Action, Box<dyn ReplyReceiverAny>), DeserializationError>;
+
+    /// Human-readable name of the request type, as returned by
+    /// `any::type_name`.
+    fn request_type_name(&self) -> &'static str;
+
+    /// Human-readable name of the reply type, as returned by
+    /// `any::type_name`.
+    fn reply_type_name(&self) -> &'static str;
+}
+
+impl<T, R> QuerySourceAny for QuerySource<T, R>
+where
+    T: DeserializeOwned + Clone + Send + 'static,
+    R: Serialize + Send + 'static,
+{
+    fn query(
+        &self,
+        arg: &[u8],
+    ) -> Result<(Action, Box<dyn ReplyReceiverAny>), DeserializationError> {
+        ciborium::from_reader(arg).map(|arg| {
+            let (action, reply_recv) = self.query(arg);
+            let reply_recv: Box<dyn ReplyReceiverAny> = Box::new(reply_recv);
+
+            (action, reply_recv)
+        })
+    }
+
+    fn request_type_name(&self) -> &'static str {
+        std::any::type_name::<T>()
+    }
+
+    fn reply_type_name(&self) -> &'static str {
+        std::any::type_name::<R>()
+    }
+}
+
+/// A type-erased `ReplyReceiver` that returns CBOR-encoded replies.
+pub(crate) trait ReplyReceiverAny {
+    /// Take the replies, if any, encode them and collect them in a vector.
+    fn take_collect(&mut self) -> Option<Result<Vec<Vec<u8>>, SerializationError>>;
+}
+
+impl<R: Serialize + 'static> ReplyReceiverAny for ReplyReceiver<R> {
+    fn take_collect(&mut self) -> Option<Result<Vec<Vec<u8>>, SerializationError>> {
+        let replies = self.take()?;
+
+        let encoded_replies = (move || {
+            let mut encoded_replies = Vec::new();
+            for reply in replies {
+                let mut encoded_reply = Vec::new();
+                ciborium::into_writer(&reply, &mut encoded_reply)?;
+                encoded_replies.push(encoded_reply);
+            }
+
+            Ok(encoded_replies)
+        })();
+
+        Some(encoded_replies)
+    }
+}

nexosim/src/server.rs

@@ -0,0 +1,11 @@
+//! Simulation management through remote procedure calls.
+
+mod codegen;
+mod key_registry;
+mod run;
+mod services;
+
+pub use run::run;
+
+#[cfg(unix)]
+pub use run::run_local;

nexosim/src/server/api/simulation.proto

@@ -0,0 +1,198 @@
+// The main simulation protocol.
+
+syntax = "proto3";
+package simulation.v1;
+
+import "google/protobuf/duration.proto";
+import "google/protobuf/timestamp.proto";
+import "google/protobuf/empty.proto";
+
+enum ErrorCode {
+  INTERNAL_ERROR = 0;
+  MISSING_ARGUMENT = 1;
+  INVALID_TIME = 2;
+  INVALID_PERIOD = 3;
+  INVALID_DEADLINE = 4;
+  INVALID_MESSAGE = 5;
+  INVALID_KEY = 6;
+  INITIALIZER_PANIC = 10;
+  SIMULATION_NOT_STARTED = 11;
+  SIMULATION_HALTED = 12;
+  SIMULATION_TERMINATED = 13;
+  SIMULATION_DEADLOCK = 14;
+  SIMULATION_MESSAGE_LOSS = 15;
+  SIMULATION_NO_RECIPIENT = 16;
+  SIMULATION_PANIC = 17;
+  SIMULATION_TIMEOUT = 18;
+  SIMULATION_OUT_OF_SYNC = 19;
+  SIMULATION_BAD_QUERY = 20;
+  SIMULATION_TIME_OUT_OF_RANGE = 21;
+  SOURCE_NOT_FOUND = 30;
+  SINK_NOT_FOUND = 31;
+}
+
+message Error {
+  ErrorCode code = 1;
+  string message = 2;
+}
+
+message EventKey {
+  uint64 subkey1 = 1;
+  uint64 subkey2 = 2;
+}
+
+message InitRequest { bytes cfg = 2; }
+message InitReply {
+  oneof result { // Always returns exactly 1 variant.
+    google.protobuf.Empty empty = 1;
+    Error error = 100;
+  }
+}
+
+message HaltRequest {}
+message HaltReply {
+  oneof result { // Always returns exactly 1 variant.
+    google.protobuf.Empty empty = 1;
+    Error error = 100;
+  }
+}
+
+message TimeRequest {}
+message TimeReply {
+  oneof result { // Always returns exactly 1 variant.
+    google.protobuf.Timestamp time = 1;
+    Error error = 100;
+  }
+}
+
+message StepRequest {}
+message StepReply {
+  oneof result { // Always returns exactly 1 variant.
+    google.protobuf.Timestamp time = 1;
+    Error error = 100;
+  }
+}
+
+message StepUntilRequest {
+  oneof deadline { // Always returns exactly 1 variant.
+    google.protobuf.Timestamp time = 1;
+    google.protobuf.Duration duration = 2;
+  }
+}
+message StepUntilReply {
+  oneof result { // Always returns exactly 1 variant.
+    google.protobuf.Timestamp time = 1;
+    Error error = 100;
+  }
+}
+
+message ScheduleEventRequest {
+  oneof deadline { // Expects exactly 1 variant.
+    google.protobuf.Timestamp time = 1;
+    google.protobuf.Duration duration = 2;
+  }
+  string source_name = 3;
+  bytes event = 4;
+  google.protobuf.Duration period = 5;
+  bool with_key = 6;
+}
+message ScheduleEventReply {
+  oneof result { // Always returns exactly 1 variant.
+    google.protobuf.Empty empty = 1;
+    EventKey key = 2;
+    Error error = 100;
+  }
+}
+
+message CancelEventRequest { EventKey key = 1; }
+message CancelEventReply {
+  oneof result { // Always returns exactly 1 variant.
+    google.protobuf.Empty empty = 1;
+    Error error = 100;
+  }
+}
+
+message ProcessEventRequest {
+  string source_name = 1;
+  bytes event = 2;
+}
+message ProcessEventReply {
+  oneof result { // Always returns exactly 1 variant.
+    google.protobuf.Empty empty = 1;
+    Error error = 100;
+  }
+}
+
+message ProcessQueryRequest {
+  string source_name = 1;
+  bytes request = 2;
+}
+message ProcessQueryReply {
+  // This field is hoisted because protobuf3 does not support `repeated` within
+  // a `oneof`. It is Always empty if an error is returned
+  repeated bytes replies = 1;
+  oneof result { // Always returns exactly 1 variant.
+    google.protobuf.Empty empty = 10;
+    Error error = 100;
+  }
+}
+
+message ReadEventsRequest { string sink_name = 1; }
+message ReadEventsReply {
+  // This field is hoisted because protobuf3 does not support `repeated` within
+  // a `oneof`. It is Always empty if an error is returned
+  repeated bytes events = 1;
+  oneof result { // Always returns exactly 1 variant.
+    google.protobuf.Empty empty = 10;
+    Error error = 100;
+  }
+}
+
+message OpenSinkRequest { string sink_name = 1; }
+message OpenSinkReply {
+  oneof result { // Always returns exactly 1 variant.
+    google.protobuf.Empty empty = 10;
+    Error error = 100;
+  }
+}
+
+message CloseSinkRequest { string sink_name = 1; }
+message CloseSinkReply {
+  oneof result { // Always returns exactly 1 variant.
+    google.protobuf.Empty empty = 10;
+    Error error = 100;
+  }
+}
+
+// A convenience message type for custom transport implementation.
+message AnyRequest {
+  oneof request { // Expects exactly 1 variant.
+    InitRequest init_request = 1;
+    HaltRequest halt_request = 2;
+    TimeRequest time_request = 3;
+    StepRequest step_request = 4;
+    StepUntilRequest step_until_request = 5;
+    ScheduleEventRequest schedule_event_request = 6;
+    CancelEventRequest cancel_event_request = 7;
+    ProcessEventRequest process_event_request = 8;
+    ProcessQueryRequest process_query_request = 9;
+    ReadEventsRequest read_events_request = 10;
+    OpenSinkRequest open_sink_request = 11;
+    CloseSinkRequest close_sink_request = 12;
+  }
+}
+
+service Simulation {
+  rpc Init(InitRequest) returns (InitReply);
+  rpc Halt(HaltRequest) returns (HaltReply);
+  rpc Time(TimeRequest) returns (TimeReply);
+  rpc Step(StepRequest) returns (StepReply);
+  rpc StepUntil(StepUntilRequest) returns (StepUntilReply);
+  rpc ScheduleEvent(ScheduleEventRequest) returns (ScheduleEventReply);
+  rpc CancelEvent(CancelEventRequest) returns (CancelEventReply);
+  rpc ProcessEvent(ProcessEventRequest) returns (ProcessEventReply);
+  rpc ProcessQuery(ProcessQueryRequest) returns (ProcessQueryReply);
+  rpc ReadEvents(ReadEventsRequest) returns (ReadEventsReply);
+  rpc OpenSink(OpenSinkRequest) returns (OpenSinkReply);
+  rpc CloseSink(CloseSinkRequest) returns (CloseSinkReply);
+}

nexosim/src/server/codegen.rs

@@ -0,0 +1,7 @@
+#![allow(unreachable_pub)]
+#![allow(clippy::enum_variant_names)]
+#![allow(missing_docs)]
+
+#[rustfmt::skip]
+#[path = "codegen/simulation.v1.rs"]
+pub(crate) mod simulation;

nexosim/src/server/key_registry.rs

@@ -0,0 +1,48 @@
+use crate::simulation::ActionKey;
+use crate::time::MonotonicTime;
+use crate::util::indexed_priority_queue::{IndexedPriorityQueue, InsertKey};
+
+pub(crate) type KeyRegistryId = InsertKey;
+
+/// A collection of `ActionKey`s indexed by a unique identifier.
+#[derive(Default)]
+pub(crate) struct KeyRegistry {
+    keys: IndexedPriorityQueue<MonotonicTime, ActionKey>,
+}
+
+impl KeyRegistry {
+    /// Inserts an `ActionKey` into the registry.
+    ///
+    /// The provided expiration deadline is the latest time at which the key is
+    /// guaranteed to be extractable.
+    pub(crate) fn insert_key(
+        &mut self,
+        action_key: ActionKey,
+        expiration: MonotonicTime,
+    ) -> KeyRegistryId {
+        self.keys.insert(expiration, action_key)
+    }
+
+    /// Inserts a non-expiring `ActionKey` into the registry.
+    pub(crate) fn insert_eternal_key(&mut self, action_key: ActionKey) -> KeyRegistryId {
+        self.keys.insert(MonotonicTime::MAX, action_key)
+    }
+
+    /// Removes an `ActionKey` from the registry and returns it.
+    ///
+    /// Returns `None` if the key was not found in the registry.
+    pub(crate) fn extract_key(&mut self, key_id: KeyRegistryId) -> Option<ActionKey> {
+        self.keys.extract(key_id).map(|(_, key)| key)
+    }
+
+    /// Remove keys with an expiration deadline strictly predating the argument.
+    pub(crate) fn remove_expired_keys(&mut self, now: MonotonicTime) {
+        while let Some(expiration) = self.keys.peek_key() {
+            if *expiration >= now {
+                return;
+            }
+
+            self.keys.pull();
+        }
+    }
+}

nexosim/src/server/run.rs

@@ -0,0 +1,293 @@
+//! Simulation server.
+
+use std::net::SocketAddr;
+#[cfg(unix)]
+use std::path::Path;
+use std::sync::Arc;
+use std::sync::Mutex;
+use std::sync::MutexGuard;
+
+use serde::de::DeserializeOwned;
+use tonic::{transport::Server, Request, Response, Status};
+
+use crate::registry::EndpointRegistry;
+use crate::simulation::{Simulation, SimulationError};
+
+use super::codegen::simulation::*;
+use super::key_registry::KeyRegistry;
+use super::services::InitService;
+use super::services::{ControllerService, MonitorService, SchedulerService};
+
+/// Runs a simulation from a network server.
+///
+/// The first argument is a closure that takes an initialization configuration
+/// and is called every time the simulation is (re)started by the remote client.
+/// It must create a new simulation, complemented by a registry that exposes the
+/// public event and query interface.
+pub fn run<F, I>(sim_gen: F, addr: SocketAddr) -> Result<(), Box<dyn std::error::Error>>
+where
+    F: FnMut(I) -> Result<(Simulation, EndpointRegistry), SimulationError> + Send + 'static,
+    I: DeserializeOwned,
+{
+    run_service(GrpcSimulationService::new(sim_gen), addr)
+}
+
+/// Monomorphization of the network server.
+///
+/// Keeping this as a separate monomorphized fragment can even triple
+/// compilation speed for incremental release builds.
+fn run_service(
+    service: GrpcSimulationService,
+    addr: SocketAddr,
+) -> Result<(), Box<dyn std::error::Error>> {
+    // Use 2 threads so that even if the controller service is blocked due to
+    // ongoing simulation execution, other services can still be used
+    // concurrently.
+    let rt = tokio::runtime::Builder::new_multi_thread()
+        .worker_threads(2)
+        .enable_io()
+        .build()?;
+
+    rt.block_on(async move {
+        Server::builder()
+            .add_service(simulation_server::SimulationServer::new(service))
+            .serve(addr)
+            .await?;
+
+        Ok(())
+    })
+}
+
+/// Runs a simulation locally from a Unix Domain Sockets server.
+///
+/// The first argument is a closure that takes an initialization configuration
+/// and is called every time the simulation is (re)started by the remote client.
+/// It must create a new simulation, complemented by a registry that exposes the
+/// public event and query interface.
+#[cfg(unix)]
+pub fn run_local<F, I, P>(sim_gen: F, path: P) -> Result<(), Box<dyn std::error::Error>>
+where
+    F: FnMut(I) -> Result<(Simulation, EndpointRegistry), SimulationError> + Send + 'static,
+    I: DeserializeOwned,
+    P: AsRef<Path>,
+{
+    let path = path.as_ref();
+    run_local_service(GrpcSimulationService::new(sim_gen), path)
+}
+
+/// Monomorphization of the Unix Domain Sockets server.
+///
+/// Keeping this as a separate monomorphized fragment can even triple
+/// compilation speed for incremental release builds.
+#[cfg(unix)]
+fn run_local_service(
+    service: GrpcSimulationService,
+    path: &Path,
+) -> Result<(), Box<dyn std::error::Error>> {
+    use std::fs;
+    use std::io;
+    use std::os::unix::fs::FileTypeExt;
+
+    use tokio::net::UnixListener;
+    use tokio_stream::wrappers::UnixListenerStream;
+
+    // Unlink the socket if it already exists to prevent an `AddrInUse` error.
+    match fs::metadata(path) {
+        // The path is valid: make sure it actually points to a socket.
+        Ok(socket_meta) => {
+            if !socket_meta.file_type().is_socket() {
+                return Err(Box::new(io::Error::new(
+                    io::ErrorKind::AlreadyExists,
+                    "the specified path points to an existing non-socket file",
+                )));
+            }
+
+            fs::remove_file(path)?;
+        }
+        // Nothing to do: the socket does not exist yet.
+        Err(e) if e.kind() == io::ErrorKind::NotFound => {}
+        // We don't have permission to use the socket.
+        Err(e) => return Err(Box::new(e)),
+    }
+
+    // (Re-)Create the socket.
+    fs::create_dir_all(path.parent().unwrap())?;
+
+    // Use 2 threads so that even if the controller service is blocked due to
+    // ongoing simulation execution, other services can still be used
+    // concurrently.
+    let rt = tokio::runtime::Builder::new_multi_thread()
+        .worker_threads(2)
+        .enable_io()
+        .build()?;
+
+    rt.block_on(async move {
+        let uds = UnixListener::bind(path)?;
+        let uds_stream = UnixListenerStream::new(uds);
+
+        Server::builder()
+            .add_service(simulation_server::SimulationServer::new(service))
+            .serve_with_incoming(uds_stream)
+            .await?;
+
+        Ok(())
+    })
+}
+
+struct GrpcSimulationService {
+    init_service: Mutex<InitService>,
+    controller_service: Mutex<ControllerService>,
+    monitor_service: Mutex<MonitorService>,
+    scheduler_service: Mutex<SchedulerService>,
+}
+
+impl GrpcSimulationService {
+    /// Creates a new `GrpcSimulationService` without any active simulation.
+    ///
+    /// The argument is a closure that takes an initialization configuration and
+    /// is called every time the simulation is (re)started by the remote client.
+    /// It must create a new simulation, complemented by a registry that exposes
+    /// the public event and query interface.
+    pub(crate) fn new<F, I>(sim_gen: F) -> Self
+    where
+        F: FnMut(I) -> Result<(Simulation, EndpointRegistry), SimulationError> + Send + 'static,
+        I: DeserializeOwned,
+    {
+        Self {
+            init_service: Mutex::new(InitService::new(sim_gen)),
+            controller_service: Mutex::new(ControllerService::NotStarted),
+            monitor_service: Mutex::new(MonitorService::NotStarted),
+            scheduler_service: Mutex::new(SchedulerService::NotStarted),
+        }
+    }
+
+    /// Locks the initializer and returns the mutex guard.
+    fn initializer(&self) -> MutexGuard<'_, InitService> {
+        self.init_service.lock().unwrap()
+    }
+
+    /// Locks the controller and returns the mutex guard.
+    fn controller(&self) -> MutexGuard<'_, ControllerService> {
+        self.controller_service.lock().unwrap()
+    }
+
+    /// Locks the monitor and returns the mutex guard.
+    fn monitor(&self) -> MutexGuard<'_, MonitorService> {
+        self.monitor_service.lock().unwrap()
+    }
+
+    /// Locks the scheduler and returns the mutex guard.
+    fn scheduler(&self) -> MutexGuard<'_, SchedulerService> {
+        self.scheduler_service.lock().unwrap()
+    }
+}
+
+#[tonic::async_trait]
+impl simulation_server::Simulation for GrpcSimulationService {
+    async fn init(&self, request: Request<InitRequest>) -> Result<Response<InitReply>, Status> {
+        let request = request.into_inner();
+
+        let (reply, bench) = self.initializer().init(request);
+
+        if let Some((simulation, scheduler, endpoint_registry)) = bench {
+            let event_source_registry = Arc::new(endpoint_registry.event_source_registry);
+            let query_source_registry = endpoint_registry.query_source_registry;
+            let event_sink_registry = endpoint_registry.event_sink_registry;
+
+            *self.controller() = ControllerService::Started {
+                simulation,
+                event_source_registry: event_source_registry.clone(),
+                query_source_registry,
+            };
+            *self.monitor() = MonitorService::Started {
+                event_sink_registry,
+            };
+            *self.scheduler() = SchedulerService::Started {
+                scheduler,
+                event_source_registry,
+                key_registry: KeyRegistry::default(),
+            };
+        }
+
+        Ok(Response::new(reply))
+    }
+    async fn halt(&self, request: Request<HaltRequest>) -> Result<Response<HaltReply>, Status> {
+        let request = request.into_inner();
+
+        Ok(Response::new(self.scheduler().halt(request)))
+    }
+    async fn time(&self, request: Request<TimeRequest>) -> Result<Response<TimeReply>, Status> {
+        let request = request.into_inner();
+
+        Ok(Response::new(self.scheduler().time(request)))
+    }
+    async fn step(&self, request: Request<StepRequest>) -> Result<Response<StepReply>, Status> {
+        let request = request.into_inner();
+
+        Ok(Response::new(self.controller().step(request)))
+    }
+    async fn step_until(
+        &self,
+        request: Request<StepUntilRequest>,
+    ) -> Result<Response<StepUntilReply>, Status> {
+        let request = request.into_inner();
+
+        Ok(Response::new(self.controller().step_until(request)))
+    }
+    async fn schedule_event(
+        &self,
+        request: Request<ScheduleEventRequest>,
+    ) -> Result<Response<ScheduleEventReply>, Status> {
+        let request = request.into_inner();
+
+        Ok(Response::new(self.scheduler().schedule_event(request)))
+    }
+    async fn cancel_event(
+        &self,
+        request: Request<CancelEventRequest>,
+    ) -> Result<Response<CancelEventReply>, Status> {
+        let request = request.into_inner();
+
+        Ok(Response::new(self.scheduler().cancel_event(request)))
+    }
+    async fn process_event(
+        &self,
+        request: Request<ProcessEventRequest>,
+    ) -> Result<Response<ProcessEventReply>, Status> {
+        let request = request.into_inner();
+
+        Ok(Response::new(self.controller().process_event(request)))
+    }
+    async fn process_query(
+        &self,
+        request: Request<ProcessQueryRequest>,
+    ) -> Result<Response<ProcessQueryReply>, Status> {
+        let request = request.into_inner();
+
+        Ok(Response::new(self.controller().process_query(request)))
+    }
+    async fn read_events(
+        &self,
+        request: Request<ReadEventsRequest>,
+    ) -> Result<Response<ReadEventsReply>, Status> {
+        let request = request.into_inner();
+
+        Ok(Response::new(self.monitor().read_events(request)))
+    }
+    async fn open_sink(
+        &self,
+        request: Request<OpenSinkRequest>,
+    ) -> Result<Response<OpenSinkReply>, Status> {
+        let request = request.into_inner();
+
+        Ok(Response::new(self.monitor().open_sink(request)))
+    }
+    async fn close_sink(
+        &self,
+        request: Request<CloseSinkRequest>,
+    ) -> Result<Response<CloseSinkReply>, Status> {
+        let request = request.into_inner();
+
+        Ok(Response::new(self.monitor().close_sink(request)))
+    }
+}

nexosim/src/server/services.rs

@@ -0,0 +1,139 @@
+mod controller_service;
+mod init_service;
+mod monitor_service;
+mod scheduler_service;
+
+use std::time::Duration;
+
+use prost_types::Timestamp;
+use tai_time::MonotonicTime;
+
+use super::codegen::simulation::{Error, ErrorCode};
+use crate::simulation::{ExecutionError, SchedulingError, SimulationError};
+
+pub(crate) use controller_service::ControllerService;
+pub(crate) use init_service::InitService;
+pub(crate) use monitor_service::MonitorService;
+pub(crate) use scheduler_service::SchedulerService;
+
+/// Transforms an error code and a message into a Protobuf error.
+fn to_error(code: ErrorCode, message: impl Into<String>) -> Error {
+    Error {
+        code: code as i32,
+        message: message.into(),
+    }
+}
+
+/// An error returned when a simulation was not started.
+fn simulation_not_started_error() -> Error {
+    to_error(
+        ErrorCode::SimulationNotStarted,
+        "the simulation was not started",
+    )
+}
+
+/// Map an `ExecutionError` to a Protobuf error.
+fn map_execution_error(error: ExecutionError) -> Error {
+    let error_code = match error {
+        ExecutionError::Deadlock(_) => ErrorCode::SimulationDeadlock,
+        ExecutionError::MessageLoss(_) => ErrorCode::SimulationMessageLoss,
+        ExecutionError::NoRecipient { .. } => ErrorCode::SimulationNoRecipient,
+        ExecutionError::Panic { .. } => ErrorCode::SimulationPanic,
+        ExecutionError::Timeout => ErrorCode::SimulationTimeout,
+        ExecutionError::OutOfSync(_) => ErrorCode::SimulationOutOfSync,
+        ExecutionError::BadQuery => ErrorCode::SimulationBadQuery,
+        ExecutionError::Halted => ErrorCode::SimulationHalted,
+        ExecutionError::Terminated => ErrorCode::SimulationTerminated,
+        ExecutionError::InvalidDeadline(_) => ErrorCode::InvalidDeadline,
+    };
+
+    let error_message = error.to_string();
+
+    to_error(error_code, error_message)
+}
+
+/// Map a `SchedulingError` to a Protobuf error.
+fn map_scheduling_error(error: SchedulingError) -> Error {
+    let error_code = match error {
+        SchedulingError::InvalidScheduledTime => ErrorCode::InvalidDeadline,
+        SchedulingError::NullRepetitionPeriod => ErrorCode::InvalidPeriod,
+    };
+
+    let error_message = error.to_string();
+
+    to_error(error_code, error_message)
+}
+
+/// Map a `SimulationError` to a Protobuf error.
+fn map_simulation_error(error: SimulationError) -> Error {
+    match error {
+        SimulationError::ExecutionError(e) => map_execution_error(e),
+        SimulationError::SchedulingError(e) => map_scheduling_error(e),
+    }
+}
+
+/// Attempts a cast from a `MonotonicTime` to a protobuf `Timestamp`.
+///
+/// This will fail if the time is outside the protobuf-specified range for
+/// timestamps (0001-01-01 00:00:00 to 9999-12-31 23:59:59).
+pub(crate) fn monotonic_to_timestamp(monotonic_time: MonotonicTime) -> Option<Timestamp> {
+    // Unix timestamp for 0001-01-01 00:00:00, the minimum accepted by
+    // protobuf's specification for the `Timestamp` type.
+    const MIN_SECS: i64 = -62135596800;
+    // Unix timestamp for 9999-12-31 23:59:59, the maximum accepted by
+    // protobuf's specification for the `Timestamp` type.
+    const MAX_SECS: i64 = 253402300799;
+
+    let secs = monotonic_time.as_secs();
+    if !(MIN_SECS..=MAX_SECS).contains(&secs) {
+        return None;
+    }
+
+    Some(Timestamp {
+        seconds: secs,
+        nanos: monotonic_time.subsec_nanos() as i32,
+    })
+}
+
+/// Attempts a cast from a protobuf `Timestamp` to a `MonotonicTime`.
+///
+/// This should never fail provided that the `Timestamp` complies with the
+/// protobuf specification. It can only fail if the nanosecond part is negative
+/// or greater than 999'999'999.
+pub(crate) fn timestamp_to_monotonic(timestamp: Timestamp) -> Option<MonotonicTime> {
+    let nanos: u32 = timestamp.nanos.try_into().ok()?;
+
+    MonotonicTime::new(timestamp.seconds, nanos)
+}
+
+/// Attempts a cast from a protobuf `Duration` to a `std::time::Duration`.
+///
+/// If the `Duration` complies with the protobuf specification, this can only
+/// fail if the duration is negative.
+pub(crate) fn to_positive_duration(duration: prost_types::Duration) -> Option<Duration> {
+    if duration.seconds < 0 || duration.nanos < 0 {
+        return None;
+    }
+
+    Some(Duration::new(
+        duration.seconds as u64,
+        duration.nanos as u32,
+    ))
+}
+
+/// Attempts a cast from a protobuf `Duration` to a strictly positive
+/// `std::time::Duration`.
+///
+/// If the `Duration` complies with the protobuf specification, this can only
+/// fail if the duration is negative or null.
+pub(crate) fn to_strictly_positive_duration(duration: prost_types::Duration) -> Option<Duration> {
+    if duration.seconds < 0 || duration.nanos < 0 || (duration.seconds == 0 && duration.nanos == 0)
+    {
+        return None;
+    }
+
+    Some(Duration::new(
+        duration.seconds as u64,
+        duration.nanos as u32,
+    ))
+}

nexosim/src/server/services/controller_service.rs

@@ -0,0 +1,231 @@
+use std::fmt;
+use std::sync::Arc;
+
+use prost_types::Timestamp;
+
+use crate::registry::{EventSourceRegistry, QuerySourceRegistry};
+use crate::simulation::Simulation;
+
+use super::super::codegen::simulation::*;
+use super::{
+    map_execution_error, monotonic_to_timestamp, simulation_not_started_error,
+    timestamp_to_monotonic, to_error, to_positive_duration,
+};
+
+/// Protobuf-based simulation controller.
+///
+/// A `ControllerService` controls the execution of the simulation. Note that
+/// all its methods block until execution completes.
+#[allow(clippy::large_enum_variant)]
+pub(crate) enum ControllerService {
+    NotStarted,
+    Started {
+        simulation: Simulation,
+        event_source_registry: Arc<EventSourceRegistry>,
+        query_source_registry: QuerySourceRegistry,
+    },
+}
+
+impl ControllerService {
+    /// Advances simulation time to that of the next scheduled event, processing
+    /// that event as well as all other events scheduled for the same time.
+    ///
+    /// Processing is gated by a (possibly blocking) call to
+    /// [`Clock::synchronize`](crate::time::Clock::synchronize) on the
+    /// configured simulation clock. This method blocks until all newly
+    /// processed events have completed.
+    pub(crate) fn step(&mut self, _request: StepRequest) -> StepReply {
+        let reply = match self {
+            Self::Started { simulation, .. } => match simulation.step() {
+                Ok(()) => {
+                    if let Some(timestamp) = monotonic_to_timestamp(simulation.time()) {
+                        step_reply::Result::Time(timestamp)
+                    } else {
+                        step_reply::Result::Error(to_error(
+                            ErrorCode::SimulationTimeOutOfRange,
+                            "the final simulation time is out of range",
+                        ))
+                    }
+                }
+                Err(e) => step_reply::Result::Error(map_execution_error(e)),
+            },
+            Self::NotStarted => step_reply::Result::Error(simulation_not_started_error()),
+        };
+
+        StepReply {
+            result: Some(reply),
+        }
+    }
+
+    /// Iteratively advances the simulation time until the specified deadline,
+    /// as if by calling
+    /// [`Simulation::step`](crate::simulation::Simulation::step) repeatedly.
+    ///
+    /// This method blocks until all events scheduled up to the specified target
+    /// time have completed. The simulation time upon completion is equal to the
+    /// specified target time, whether or not an event was scheduled for that
+    /// time.
+    pub(crate) fn step_until(&mut self, request: StepUntilRequest) -> StepUntilReply {
+        let reply = match self {
+            Self::Started { simulation, .. } => move || -> Result<Timestamp, Error> {
+                let deadline = request.deadline.ok_or(to_error(
+                    ErrorCode::MissingArgument,
+                    "missing deadline argument",
+                ))?;
+
+                match deadline {
+                    step_until_request::Deadline::Time(time) => {
+                        let time = timestamp_to_monotonic(time).ok_or(to_error(
+                            ErrorCode::InvalidTime,
+                            "out-of-range nanosecond field",
+                        ))?;
+
+                        simulation.step_until(time).map_err(|_| {
+                            to_error(
+                                ErrorCode::InvalidDeadline,
+                                "the specified deadline lies in the past",
+                            )
+                        })?;
+                    }
+                    step_until_request::Deadline::Duration(duration) => {
+                        let duration = to_positive_duration(duration).ok_or(to_error(
+                            ErrorCode::InvalidDeadline,
+                            "the specified deadline lies in the past",
+                        ))?;
+
+                        simulation
+                            .step_until(duration)
+                            .map_err(map_execution_error)?;
+                    }
+                };
+
+                let timestamp = monotonic_to_timestamp(simulation.time()).ok_or(to_error(
+                    ErrorCode::SimulationTimeOutOfRange,
+                    "the final simulation time is out of range",
+                ))?;
+
+                Ok(timestamp)
+            }(),
+            Self::NotStarted => Err(simulation_not_started_error()),
+        };
+
+        StepUntilReply {
+            result: Some(match reply {
+                Ok(timestamp) => step_until_reply::Result::Time(timestamp),
+                Err(error) => step_until_reply::Result::Error(error),
+            }),
+        }
+    }
+
+    /// Broadcasts an event from an event source immediately, blocking until
+    /// completion.
+    ///
+    /// Simulation time remains unchanged.
+    pub(crate) fn process_event(&mut self, request: ProcessEventRequest) -> ProcessEventReply {
+        let reply = match self {
+            Self::Started {
+                simulation,
+                event_source_registry,
+                ..
+            } => move || -> Result<(), Error> {
+                let source_name = &request.source_name;
+                let event = &request.event;
+
+                let source = event_source_registry.get(source_name).ok_or(to_error(
+                    ErrorCode::SourceNotFound,
+                    "no source is registered with the name '{}'".to_string(),
+                ))?;
+
+                let event = source.event(event).map_err(|e| {
+                    to_error(
+                        ErrorCode::InvalidMessage,
+                        format!(
+                            "the event could not be deserialized as type '{}': {}",
+                            source.event_type_name(),
+                            e
+                        ),
+                    )
+                })?;
+
+                simulation.process(event).map_err(map_execution_error)
+            }(),
+            Self::NotStarted => Err(simulation_not_started_error()),
+        };
+
+        ProcessEventReply {
+            result: Some(match reply {
+                Ok(()) => process_event_reply::Result::Empty(()),
+                Err(error) => process_event_reply::Result::Error(error),
+            }),
+        }
+    }
+
+    /// Broadcasts a query from a query source immediately, blocking until
+    /// completion.
+    ///
+    /// Simulation time remains unchanged.
+    pub(crate) fn process_query(&mut self, request: ProcessQueryRequest) -> ProcessQueryReply {
+        let reply = match self {
+            Self::Started {
+                simulation,
+                query_source_registry,
+                ..
+            } => move || -> Result<Vec<Vec<u8>>, Error> {
+                let source_name = &request.source_name;
+                let request = &request.request;
+
+                let source = query_source_registry.get(source_name).ok_or(to_error(
+                    ErrorCode::SourceNotFound,
+                    "no source is registered with the name '{}'".to_string(),
+                ))?;
+
+                let (query, mut promise) = source.query(request).map_err(|e| {
+                    to_error(
+                        ErrorCode::InvalidMessage,
+                        format!(
+                            "the request could not be deserialized as type '{}': {}",
+                            source.request_type_name(),
+                            e
+                        ),
+                    )
+                })?;
+
+                simulation.process(query).map_err(map_execution_error)?;
+
+                let replies = promise.take_collect().ok_or(to_error(
+                    ErrorCode::SimulationBadQuery,
+                    "a reply to the query was expected but none was available; maybe the target model was not added to the simulation?".to_string(),
+                ))?;
+
+                replies.map_err(|e| {
+                    to_error(
+                        ErrorCode::InvalidMessage,
+                        format!(
+                            "the reply could not be serialized as type '{}': {}",
+                            source.reply_type_name(),
+                            e
+                        ),
+                    )
+                })
+            }(),
+            Self::NotStarted => Err(simulation_not_started_error()),
+        };
+
+        match reply {
+            Ok(replies) => ProcessQueryReply {
+                replies,
+                result: Some(process_query_reply::Result::Empty(())),
+            },
+            Err(error) => ProcessQueryReply {
+                replies: Vec::new(),
+                result: Some(process_query_reply::Result::Error(error)),
+            },
+        }
+    }
+}
+
+impl fmt::Debug for ControllerService {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ControllerService").finish_non_exhaustive()
+    }
+}

nexosim/src/server/services/init_service.rs

@@ -0,0 +1,106 @@
+use std::panic::{self, AssertUnwindSafe};
+
+use ciborium;
+use serde::de::DeserializeOwned;
+
+use crate::registry::EndpointRegistry;
+use crate::simulation::{Scheduler, Simulation, SimulationError};
+
+use super::{map_simulation_error, to_error};
+
+use super::super::codegen::simulation::*;
+
+type InitResult = Result<(Simulation, EndpointRegistry), SimulationError>;
+type DeserializationError = ciborium::de::Error<std::io::Error>;
+type SimGen = Box<dyn FnMut(&[u8]) -> Result<InitResult, DeserializationError> + Send + 'static>;
+
+/// Protobuf-based simulation initializer.
+///
+/// An `InitService` creates a new simulation bench based on a serialized
+/// initialization configuration.
+pub(crate) struct InitService {
+    sim_gen: SimGen,
+}
+
+impl InitService {
+    /// Creates a new `InitService`.
+    ///
+    /// The argument is a closure that takes a CBOR-serialized initialization
+    /// configuration and is called every time the simulation is (re)started by
+    /// the remote client. It must create a new simulation complemented by a
+    /// registry that exposes the public event and query interface.
+    pub(crate) fn new<F, I>(mut sim_gen: F) -> Self
+    where
+        F: FnMut(I) -> Result<(Simulation, EndpointRegistry), SimulationError> + Send + 'static,
+        I: DeserializeOwned,
+    {
+        // Wrap `sim_gen` so it accepts a serialized init configuration.
+        let sim_gen = move |serialized_cfg: &[u8]| -> Result<InitResult, DeserializationError> {
+            let cfg = ciborium::from_reader(serialized_cfg)?;
+
+            Ok(sim_gen(cfg))
+        };
+
+        Self {
+            sim_gen: Box::new(sim_gen),
+        }
+    }
+
+    /// Initializes the simulation based on the specified configuration.
+    pub(crate) fn init(
+        &mut self,
+        request: InitRequest,
+    ) -> (InitReply, Option<(Simulation, Scheduler, EndpointRegistry)>) {
+        let reply = panic::catch_unwind(AssertUnwindSafe(|| (self.sim_gen)(&request.cfg)))
+            .map_err(|payload| {
+                let panic_msg: Option<&str> = if let Some(s) = payload.downcast_ref::<&str>() {
+                    Some(s)
+                } else if let Some(s) = payload.downcast_ref::<String>() {
+                    Some(s)
+                } else {
+                    None
+                };
+
+                let error_msg = if let Some(panic_msg) = panic_msg {
+                    format!(
+                        "the simulation initializer has panicked with the message `{}`",
+                        panic_msg
+                    )
+                } else {
+                    String::from("the simulation initializer has panicked")
+                };
+
+                to_error(ErrorCode::InitializerPanic, error_msg)
+            })
+            .and_then(|res| {
+                res.map_err(|e| {
+                    to_error(
+                        ErrorCode::InvalidMessage,
+                        format!(
+                            "the initializer configuration could not be deserialized: {}",
+                            e
+                        ),
+                    )
+                })
+                .and_then(|init_result| init_result.map_err(map_simulation_error))
+            });
+
+        let (reply, bench) = match reply {
+            Ok((simulation, registry)) => {
+                let scheduler = simulation.scheduler();
+                (
+                    init_reply::Result::Empty(()),
+                    Some((simulation, scheduler, registry)),
+                )
+            }
+            Err(e) => (init_reply::Result::Error(e), None),
+        };
+
+        (
+            InitReply {
+                result: Some(reply),
+            },
+            bench,
+        )
+    }
+}

nexosim/src/server/services/monitor_service.rs

@@ -0,0 +1,118 @@
+use std::fmt;
+
+use crate::registry::EventSinkRegistry;
+
+use super::super::codegen::simulation::*;
+use super::{simulation_not_started_error, to_error};
+
+/// Protobuf-based simulation monitor.
+///
+/// A `MonitorService` enables the monitoring of the event sinks of a
+/// [`Simulation`](crate::simulation::Simulation).
+pub(crate) enum MonitorService {
+    Started {
+        event_sink_registry: EventSinkRegistry,
+    },
+    NotStarted,
+}
+
+impl MonitorService {
+    /// Read all events from an event sink.
+    pub(crate) fn read_events(&mut self, request: ReadEventsRequest) -> ReadEventsReply {
+        let reply = match self {
+            Self::Started {
+                event_sink_registry,
+            } => move || -> Result<Vec<Vec<u8>>, Error> {
+                let sink_name = &request.sink_name;
+
+                let sink = event_sink_registry.get_mut(sink_name).ok_or(to_error(
+                    ErrorCode::SinkNotFound,
+                    format!("no sink is registered with the name '{}'", sink_name),
+                ))?;
+
+                sink.collect().map_err(|e| {
+                    to_error(
+                        ErrorCode::InvalidMessage,
+                        format!(
+                            "the event could not be serialized from type '{}': {}",
+                            sink.event_type_name(),
+                            e
+                        ),
+                    )
+                })
+            }(),
+            Self::NotStarted => Err(simulation_not_started_error()),
+        };
+
+        match reply {
+            Ok(events) => ReadEventsReply {
+                events,
+                result: Some(read_events_reply::Result::Empty(())),
+            },
+            Err(error) => ReadEventsReply {
+                events: Vec::new(),
+                result: Some(read_events_reply::Result::Error(error)),
+            },
+        }
+    }
+
+    /// Opens an event sink.
+    pub(crate) fn open_sink(&mut self, request: OpenSinkRequest) -> OpenSinkReply {
+        let reply = match self {
+            Self::Started {
+                event_sink_registry,
+            } => {
+                let sink_name = &request.sink_name;
+
+                if let Some(sink) = event_sink_registry.get_mut(sink_name) {
+                    sink.open();
+
+                    open_sink_reply::Result::Empty(())
+                } else {
+                    open_sink_reply::Result::Error(to_error(
+                        ErrorCode::SinkNotFound,
+                        format!("no sink is registered with the name '{}'", sink_name),
+                    ))
+                }
+            }
+            Self::NotStarted => open_sink_reply::Result::Error(simulation_not_started_error()),
+        };
+
+        OpenSinkReply {
+            result: Some(reply),
+        }
+    }
+
+    /// Closes an event sink.
+    pub(crate) fn close_sink(&mut self, request: CloseSinkRequest) -> CloseSinkReply {
+        let reply = match self {
+            Self::Started {
+                event_sink_registry,
+            } => {
+                let sink_name = &request.sink_name;
+
+                if let Some(sink) = event_sink_registry.get_mut(sink_name) {
+                    sink.close();
+
+                    close_sink_reply::Result::Empty(())
+                } else {
+                    close_sink_reply::Result::Error(to_error(
+                        ErrorCode::SinkNotFound,
+                        format!("no sink is registered with the name '{}'", sink_name),
+                    ))
+                }
+            }
+            Self::NotStarted => close_sink_reply::Result::Error(simulation_not_started_error()),
+        };
+
+        CloseSinkReply {
+            result: Some(reply),
+        }
+    }
+}
+
+impl fmt::Debug for MonitorService {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SimulationService").finish_non_exhaustive()
+    }
+}

nexosim/src/server/services/scheduler_service.rs

@@ -0,0 +1,216 @@
+use std::fmt;
+use std::sync::Arc;
+
+use crate::registry::EventSourceRegistry;
+use crate::server::key_registry::{KeyRegistry, KeyRegistryId};
+use crate::simulation::Scheduler;
+
+use super::super::codegen::simulation::*;
+use super::{
+    map_scheduling_error, monotonic_to_timestamp, simulation_not_started_error,
+    timestamp_to_monotonic, to_error, to_strictly_positive_duration,
+};
+
+/// Protobuf-based simulation scheduler.
+///
+/// A `SchedulerService` enables the scheduling of simulation events.
+#[allow(clippy::large_enum_variant)]
+pub(crate) enum SchedulerService {
+    NotStarted,
+    Started {
+        scheduler: Scheduler,
+        event_source_registry: Arc<EventSourceRegistry>,
+        key_registry: KeyRegistry,
+    },
+}
+
+impl SchedulerService {
+    /// Returns the current simulation time.
+    pub(crate) fn time(&mut self, _request: TimeRequest) -> TimeReply {
+        let reply = match self {
+            Self::Started { scheduler, .. } => {
+                if let Some(timestamp) = monotonic_to_timestamp(scheduler.time()) {
+                    time_reply::Result::Time(timestamp)
+                } else {
+                    time_reply::Result::Error(to_error(
+                        ErrorCode::SimulationTimeOutOfRange,
+                        "the final simulation time is out of range",
+                    ))
+                }
+            }
+            Self::NotStarted => time_reply::Result::Error(simulation_not_started_error()),
+        };
+
+        TimeReply {
+            result: Some(reply),
+        }
+    }
+
+    /// Schedules an event at a future time.
+    pub(crate) fn schedule_event(&mut self, request: ScheduleEventRequest) -> ScheduleEventReply {
+        let reply = match self {
+            Self::Started {
+                scheduler,
+                event_source_registry,
+                key_registry,
+            } => move || -> Result<Option<KeyRegistryId>, Error> {
+                let source_name = &request.source_name;
+                let event = &request.event;
+                let with_key = request.with_key;
+                let period = request
+                    .period
+                    .map(|period| {
+                        to_strictly_positive_duration(period).ok_or(to_error(
+                            ErrorCode::InvalidPeriod,
+                            "the specified event period is not strictly positive",
+                        ))
+                    })
+                    .transpose()?;
+
+                let source = event_source_registry.get(source_name).ok_or(to_error(
+                    ErrorCode::SourceNotFound,
+                    "no event source is registered with the name '{}'".to_string(),
+                ))?;
+
+                let (action, action_key) = match (with_key, period) {
+                    (false, None) => source.event(event).map(|action| (action, None)),
+                    (false, Some(period)) => source
+                        .periodic_event(period, event)
+                        .map(|action| (action, None)),
+                    (true, None) => source
+                        .keyed_event(event)
+                        .map(|(action, key)| (action, Some(key))),
+                    (true, Some(period)) => source
+                        .keyed_periodic_event(period, event)
+                        .map(|(action, key)| (action, Some(key))),
+                }
+                .map_err(|e| {
+                    to_error(
+                        ErrorCode::InvalidMessage,
+                        format!(
+                            "the event could not be deserialized as type '{}': {}",
+                            source.event_type_name(),
+                            e
+                        ),
+                    )
+                })?;
+
+                let deadline = request.deadline.ok_or(to_error(
+                    ErrorCode::MissingArgument,
+                    "missing deadline argument",
+                ))?;
+
+                let deadline = match deadline {
+                    schedule_event_request::Deadline::Time(time) => timestamp_to_monotonic(time)
+                        .ok_or(to_error(
+                            ErrorCode::InvalidTime,
+                            "out-of-range nanosecond field",
+                        ))?,
+                    schedule_event_request::Deadline::Duration(duration) => {
+                        let duration = to_strictly_positive_duration(duration).ok_or(to_error(
+                            ErrorCode::InvalidDeadline,
+                            "the specified scheduling deadline is not in the future",
+                        ))?;
+
+                        scheduler.time() + duration
+                    }
+                };
+
+                let key_id = action_key.map(|action_key| {
+                    key_registry.remove_expired_keys(scheduler.time());
+
+                    if period.is_some() {
+                        key_registry.insert_eternal_key(action_key)
+                    } else {
+                        key_registry.insert_key(action_key, deadline)
+                    }
+                });
+
+                scheduler
+                    .schedule(deadline, action)
+                    .map_err(map_scheduling_error)?;
+
+                Ok(key_id)
+            }(),
+            Self::NotStarted => Err(simulation_not_started_error()),
+        };
+
+        ScheduleEventReply {
+            result: Some(match reply {
+                Ok(Some(key_id)) => {
+                    let (subkey1, subkey2) = key_id.into_raw_parts();
+                    schedule_event_reply::Result::Key(EventKey {
+                        subkey1: subkey1
+                            .try_into()
+                            .expect("action key index is too large to be serialized"),
+                        subkey2,
+                    })
+                }
+                Ok(None) => schedule_event_reply::Result::Empty(()),
+                Err(error) => schedule_event_reply::Result::Error(error),
+            }),
+        }
+    }
+
+    /// Cancels a keyed event.
+    pub(crate) fn cancel_event(&mut self, request: CancelEventRequest) -> CancelEventReply {
+        let reply = match self {
+            Self::Started {
+                scheduler,
+                key_registry,
+                ..
+            } => move || -> Result<(), Error> {
+                let key = request
+                    .key
+                    .ok_or(to_error(ErrorCode::MissingArgument, "missing key argument"))?;
+                let subkey1: usize = key
+                    .subkey1
+                    .try_into()
+                    .map_err(|_| to_error(ErrorCode::InvalidKey, "invalid event key"))?;
+                let subkey2 = key.subkey2;
+
+                let key_id = KeyRegistryId::from_raw_parts(subkey1, subkey2);
+
+                key_registry.remove_expired_keys(scheduler.time());
+                let key = key_registry.extract_key(key_id).ok_or(to_error(
+                    ErrorCode::InvalidKey,
+                    "invalid or expired event key",
+                ))?;
+
+                key.cancel();
+
+                Ok(())
+            }(),
+            Self::NotStarted => Err(simulation_not_started_error()),
+        };
+
+        CancelEventReply {
+            result: Some(match reply {
+                Ok(()) => cancel_event_reply::Result::Empty(()),
+                Err(error) => cancel_event_reply::Result::Error(error),
+            }),
+        }
+    }
+
+    /// Requests the simulation to stop when advancing to the next step.
+    pub(crate) fn halt(&mut self, _request: HaltRequest) -> HaltReply {
+        let reply = match self {
+            Self::Started { scheduler, .. } => {
+                scheduler.halt();
+
+                halt_reply::Result::Empty(())
+            }
+            Self::NotStarted => halt_reply::Result::Error(simulation_not_started_error()),
+        };
+
+        HaltReply {
+            result: Some(reply),
+        }
+    }
+}
+
+impl fmt::Debug for SchedulerService {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SchedulerService").finish_non_exhaustive()
+    }
+}

nexosim/src/simulation/mailbox.rs

@@ -8,7 +8,7 @@ use crate::model::Model;
 /// A mailbox is an entity associated to a model instance that collects all
 /// messages sent to that model. The size of its internal buffer can be
 /// optionally specified at construction time using
-/// [`with_capacity()`](Mailbox::with_capacity).
+/// [`with_capacity`](Mailbox::with_capacity).
 pub struct Mailbox<M: Model>(pub(crate) Receiver<M>);
 
 impl<M: Model> Mailbox<M> {
@@ -58,7 +58,7 @@ impl<M: Model> fmt::Debug for Mailbox<M> {
 /// For the sake of convenience, methods that require an address by value will
 /// typically also accept an `&Address` or an `&Mailbox` since these references
 /// implement the `Into<Address>` trait, automatically invoking
-/// `Address::clone()` or `Mailbox::address()` as appropriate.
+/// `Address::clone` or `Mailbox::address` as appropriate.
 pub struct Address<M: Model>(pub(crate) Sender<M>);
 
 impl<M: Model> Clone for Address<M> {
@@ -80,8 +80,7 @@ impl<M: Model> From<&Address<M>> for Address<M> {
 impl<M: Model> From<&Mailbox<M>> for Address<M> {
     /// Converts a [Mailbox] reference into an [`Address`].
     ///
-    /// This calls [`Mailbox::address()`] on the mailbox and returns the
-    /// address.
+    /// This calls [`Mailbox::address`] on the mailbox and returns the address.
     #[inline]
     fn from(s: &Mailbox<M>) -> Address<M> {
         s.address()

nexosim/src/simulation/scheduler.rs

@@ -0,0 +1,855 @@
+//! Scheduling functions and types.
+use std::error::Error;
+use std::future::Future;
+use std::hash::{Hash, Hasher};
+use std::pin::Pin;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::{Arc, Mutex};
+use std::task::{Context, Poll};
+use std::time::Duration;
+use std::{fmt, ptr};
+
+use pin_project::pin_project;
+use recycle_box::{coerce_box, RecycleBox};
+
+use crate::channel::Sender;
+use crate::executor::Executor;
+use crate::model::Model;
+use crate::ports::InputFn;
+use crate::simulation::Address;
+use crate::time::{AtomicTimeReader, Deadline, MonotonicTime};
+use crate::util::priority_queue::PriorityQueue;
+
+#[cfg(all(test, not(nexosim_loom)))]
+use crate::{time::TearableAtomicTime, util::sync_cell::SyncCell};
+
+const GLOBAL_SCHEDULER_ORIGIN_ID: usize = 0;
+
+/// A global simulation scheduler.
+///
+/// A `Scheduler` can be `Clone`d and sent to other threads.
+#[derive(Clone)]
+pub struct Scheduler(GlobalScheduler);
+
+impl Scheduler {
+    pub(crate) fn new(
+        scheduler_queue: Arc<Mutex<SchedulerQueue>>,
+        time: AtomicTimeReader,
+        is_halted: Arc<AtomicBool>,
+    ) -> Self {
+        Self(GlobalScheduler::new(scheduler_queue, time, is_halted))
+    }
+
+    /// Returns the current simulation time.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use nexosim::simulation::Scheduler;
+    /// use nexosim::time::MonotonicTime;
+    ///
+    /// fn is_third_millenium(scheduler: &Scheduler) -> bool {
+    ///     let time = scheduler.time();
+    ///     time >= MonotonicTime::new(978307200, 0).unwrap()
+    ///         && time < MonotonicTime::new(32535216000, 0).unwrap()
+    /// }
+    /// ```
+    pub fn time(&self) -> MonotonicTime {
+        self.0.time()
+    }
+
+    /// Schedules an action at a future time.
+    ///
+    /// An error is returned if the specified time is not in the future of the
+    /// current simulation time.
+    ///
+    /// If multiple actions send events at the same simulation time to the same
+    /// model, these events are guaranteed to be processed according to the
+    /// scheduling order of the actions.
+    pub fn schedule(&self, deadline: impl Deadline, action: Action) -> Result<(), SchedulingError> {
+        self.0
+            .schedule_from(deadline, action, GLOBAL_SCHEDULER_ORIGIN_ID)
+    }
+
+    /// Schedules an event at a future time.
+    ///
+    /// An error is returned if the specified time is not in the future of the
+    /// current simulation time.
+    ///
+    /// Events scheduled for the same time and targeting the same model are
+    /// guaranteed to be processed according to the scheduling order.
+    pub fn schedule_event<M, F, T, S>(
+        &self,
+        deadline: impl Deadline,
+        func: F,
+        arg: T,
+        address: impl Into<Address<M>>,
+    ) -> Result<(), SchedulingError>
+    where
+        M: Model,
+        F: for<'a> InputFn<'a, M, T, S>,
+        T: Send + Clone + 'static,
+        S: Send + 'static,
+    {
+        self.0
+            .schedule_event_from(deadline, func, arg, address, GLOBAL_SCHEDULER_ORIGIN_ID)
+    }
+
+    /// Schedules a cancellable event at a future time and returns an event key.
+    ///
+    /// An error is returned if the specified time is not in the future of the
+    /// current simulation time.
+    ///
+    /// Events scheduled for the same time and targeting the same model are
+    /// guaranteed to be processed according to the scheduling order.
+    pub fn schedule_keyed_event<M, F, T, S>(
+        &self,
+        deadline: impl Deadline,
+        func: F,
+        arg: T,
+        address: impl Into<Address<M>>,
+    ) -> Result<ActionKey, SchedulingError>
+    where
+        M: Model,
+        F: for<'a> InputFn<'a, M, T, S>,
+        T: Send + Clone + 'static,
+        S: Send + 'static,
+    {
+        self.0
+            .schedule_keyed_event_from(deadline, func, arg, address, GLOBAL_SCHEDULER_ORIGIN_ID)
+    }
+
+    /// Schedules a periodically recurring event at a future time.
+    ///
+    /// An error is returned if the specified time is not in the future of the
+    /// current simulation time or if the specified period is null.
+    ///
+    /// Events scheduled for the same time and targeting the same model are
+    /// guaranteed to be processed according to the scheduling order.
+    pub fn schedule_periodic_event<M, F, T, S>(
+        &self,
+        deadline: impl Deadline,
+        period: Duration,
+        func: F,
+        arg: T,
+        address: impl Into<Address<M>>,
+    ) -> Result<(), SchedulingError>
+    where
+        M: Model,
+        F: for<'a> InputFn<'a, M, T, S> + Clone,
+        T: Send + Clone + 'static,
+        S: Send + 'static,
+    {
+        self.0.schedule_periodic_event_from(
+            deadline,
+            period,
+            func,
+            arg,
+            address,
+            GLOBAL_SCHEDULER_ORIGIN_ID,
+        )
+    }
+
+    /// Schedules a cancellable, periodically recurring event at a future time
+    /// and returns an event key.
+    ///
+    /// An error is returned if the specified time is not in the future of the
+    /// current simulation time or if the specified period is null.
+    ///
+    /// Events scheduled for the same time and targeting the same model are
+    /// guaranteed to be processed according to the scheduling order.
+    pub fn schedule_keyed_periodic_event<M, F, T, S>(
+        &self,
+        deadline: impl Deadline,
+        period: Duration,
+        func: F,
+        arg: T,
+        address: impl Into<Address<M>>,
+    ) -> Result<ActionKey, SchedulingError>
+    where
+        M: Model,
+        F: for<'a> InputFn<'a, M, T, S> + Clone,
+        T: Send + Clone + 'static,
+        S: Send + 'static,
+    {
+        self.0.schedule_keyed_periodic_event_from(
+            deadline,
+            period,
+            func,
+            arg,
+            address,
+            GLOBAL_SCHEDULER_ORIGIN_ID,
+        )
+    }
+
+    /// Requests the simulation to stop when advancing to the next step.
+    pub fn halt(&mut self) {
+        self.0.halt()
+    }
+}
+
+impl fmt::Debug for Scheduler {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Scheduler")
+            .field("time", &self.time())
+            .finish_non_exhaustive()
+    }
+}
+
+/// Managed handle to a scheduled action.
+///
+/// An `AutoActionKey` is a managed handle to a scheduled action that cancels
+/// its associated action on drop.
+#[derive(Debug)]
+#[must_use = "dropping this key immediately cancels the associated action"]
+pub struct AutoActionKey {
+    is_cancelled: Arc<AtomicBool>,
+}
+
+impl Drop for AutoActionKey {
+    fn drop(&mut self) {
+        self.is_cancelled.store(true, Ordering::Relaxed);
+    }
+}
+
+/// Handle to a scheduled action.
+///
+/// An `ActionKey` can be used to cancel a scheduled action.
+#[derive(Clone, Debug)]
+#[must_use = "prefer unkeyed scheduling methods if the action is never cancelled"]
+pub struct ActionKey {
+    is_cancelled: Arc<AtomicBool>,
+}
+
+impl ActionKey {
+    /// Creates a key for a pending action.
+    pub(crate) fn new() -> Self {
+        Self {
+            is_cancelled: Arc::new(AtomicBool::new(false)),
+        }
+    }
+
+    /// Checks whether the action was cancelled.
+    pub(crate) fn is_cancelled(&self) -> bool {
+        self.is_cancelled.load(Ordering::Relaxed)
+    }
+
+    /// Cancels the associated action.
+    pub fn cancel(self) {
+        self.is_cancelled.store(true, Ordering::Relaxed);
+    }
+
+    /// Converts action key to a managed key.
+    pub fn into_auto(self) -> AutoActionKey {
+        AutoActionKey {
+            is_cancelled: self.is_cancelled,
+        }
+    }
+}
+
+impl PartialEq for ActionKey {
+    /// Implements equality by considering clones to be equivalent, rather than
+    /// keys with the same `is_cancelled` value.
+    fn eq(&self, other: &Self) -> bool {
+        ptr::eq(&*self.is_cancelled, &*other.is_cancelled)
+    }
+}
+
+impl Eq for ActionKey {}
+
+impl Hash for ActionKey {
+    /// Implements `Hash`` by considering clones to be equivalent, rather than
+    /// keys with the same `is_cancelled` value.
+    fn hash<H>(&self, state: &mut H)
+    where
+        H: Hasher,
+    {
+        ptr::hash(&*self.is_cancelled, state)
+    }
+}
+
+/// Error returned when the scheduled time or the repetition period are invalid.
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum SchedulingError {
+    /// The scheduled time does not lie in the future of the current simulation
+    /// time.
+    InvalidScheduledTime,
+    /// The repetition period is zero.
+    NullRepetitionPeriod,
+}
+
+impl fmt::Display for SchedulingError {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::InvalidScheduledTime => write!(
+                fmt,
+                "the scheduled time should be in the future of the current simulation time"
+            ),
+            Self::NullRepetitionPeriod => write!(fmt, "the repetition period cannot be zero"),
+        }
+    }
+}
+
+impl Error for SchedulingError {}
+
+/// A possibly periodic, possibly cancellable action that can be scheduled or
+/// processed immediately.
+///
+/// `Actions` can be created from an [`EventSource`](crate::ports::EventSource)
+/// or [`QuerySource`](crate::ports::QuerySource). They can be used to schedule
+/// events and requests with [`Scheduler::schedule`], or to process events and
+/// requests immediately with
+/// [`Simulation::process`](crate::simulation::Simulation::process).
+pub struct Action {
+    inner: Box<dyn ActionInner>,
+}
+
+impl Action {
+    /// Creates a new `Action` from an `ActionInner`.
+    pub(crate) fn new<S: ActionInner>(s: S) -> Self {
+        Self { inner: Box::new(s) }
+    }
+
+    /// Reports whether the action was cancelled.
+    pub(crate) fn is_cancelled(&self) -> bool {
+        self.inner.is_cancelled()
+    }
+
+    /// If this is a periodic action, returns a boxed clone of this action and
+    /// its repetition period; otherwise returns `None`.
+    pub(crate) fn next(&self) -> Option<(Action, Duration)> {
+        self.inner
+            .next()
+            .map(|(inner, period)| (Self { inner }, period))
+    }
+
+    /// Returns a boxed future that performs the action.
+    pub(crate) fn into_future(self) -> Pin<Box<dyn Future<Output = ()> + Send>> {
+        self.inner.into_future()
+    }
+
+    /// Spawns the future that performs the action onto the provided executor.
+    ///
+    /// This method is typically more efficient that spawning the boxed future
+    /// from `into_future` since it can directly spawn the unboxed future.
+    pub(crate) fn spawn_and_forget(self, executor: &Executor) {
+        self.inner.spawn_and_forget(executor)
+    }
+}
+
+impl fmt::Debug for Action {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("SchedulableEvent").finish_non_exhaustive()
+    }
+}
+
+/// Alias for the scheduler queue type.
+///
+/// Why use both time and origin ID as the key? The short answer is that this
+/// allows to preserve the relative ordering of events which have the same
+/// origin (where the origin is either a model instance or the global
+/// scheduler). The preservation of this ordering is implemented by the event
+/// loop, which aggregate events with the same origin into single sequential
+/// futures, thus ensuring that they are not executed concurrently.
+pub(crate) type SchedulerQueue = PriorityQueue<(MonotonicTime, usize), Action>;
+
+/// Internal implementation of the global scheduler.
+#[derive(Clone)]
+pub(crate) struct GlobalScheduler {
+    scheduler_queue: Arc<Mutex<SchedulerQueue>>,
+    time: AtomicTimeReader,
+    is_halted: Arc<AtomicBool>,
+}
+
+impl GlobalScheduler {
+    pub(crate) fn new(
+        scheduler_queue: Arc<Mutex<SchedulerQueue>>,
+        time: AtomicTimeReader,
+        is_halted: Arc<AtomicBool>,
+    ) -> Self {
+        Self {
+            scheduler_queue,
+            time,
+            is_halted,
+        }
+    }
+
+    /// Returns the current simulation time.
+    pub(crate) fn time(&self) -> MonotonicTime {
+        // We use `read` rather than `try_read` because the scheduler can be
+        // sent to another thread than the simulator's and could thus
+        // potentially see a torn read if the simulator increments time
+        // concurrently. The chances of this happening are very small since
+        // simulation time is not changed frequently.
+        self.time.read()
+    }
+
+    /// Schedules an action identified by its origin at a future time.
+    pub(crate) fn schedule_from(
+        &self,
+        deadline: impl Deadline,
+        action: Action,
+        origin_id: usize,
+    ) -> Result<(), SchedulingError> {
+        // The scheduler queue must always be locked when reading the time,
+        // otherwise the following race could occur:
+        // 1) this method reads the time and concludes that it is not too late
+        //    to schedule the action,
+        // 2) the `Simulation` object takes the lock, increments simulation time
+        //    and runs the simulation step,
+        // 3) this method takes the lock and schedules the now-outdated action.
+        let mut scheduler_queue = self.scheduler_queue.lock().unwrap();
+
+        let now = self.time();
+        let time = deadline.into_time(now);
+        if now >= time {
+            return Err(SchedulingError::InvalidScheduledTime);
+        }
+
+        scheduler_queue.insert((time, origin_id), action);
+
+        Ok(())
+    }
+
+    /// Schedules an event identified by its origin at a future time.
+    pub(crate) fn schedule_event_from<M, F, T, S>(
+        &self,
+        deadline: impl Deadline,
+        func: F,
+        arg: T,
+        address: impl Into<Address<M>>,
+        origin_id: usize,
+    ) -> Result<(), SchedulingError>
+    where
+        M: Model,
+        F: for<'a> InputFn<'a, M, T, S>,
+        T: Send + Clone + 'static,
+        S: Send + 'static,
+    {
+        let sender = address.into().0;
+        let action = Action::new(OnceAction::new(process_event(func, arg, sender)));
+
+        // The scheduler queue must always be locked when reading the time (see
+        // `schedule_from`).
+        let mut scheduler_queue = self.scheduler_queue.lock().unwrap();
+        let now = self.time();
+        let time = deadline.into_time(now);
+        if now >= time {
+            return Err(SchedulingError::InvalidScheduledTime);
+        }
+
+        scheduler_queue.insert((time, origin_id), action);
+
+        Ok(())
+    }
+
+    /// Schedules a cancellable event identified by its origin at a future time
+    /// and returns an event key.
+    pub(crate) fn schedule_keyed_event_from<M, F, T, S>(
+        &self,
+        deadline: impl Deadline,
+        func: F,
+        arg: T,
+        address: impl Into<Address<M>>,
+        origin_id: usize,
+    ) -> Result<ActionKey, SchedulingError>
+    where
+        M: Model,
+        F: for<'a> InputFn<'a, M, T, S>,
+        T: Send + Clone + 'static,
+        S: Send + 'static,
+    {
+        let event_key = ActionKey::new();
+        let sender = address.into().0;
+        let action = Action::new(KeyedOnceAction::new(
+            |ek| send_keyed_event(ek, func, arg, sender),
+            event_key.clone(),
+        ));
+
+        // The scheduler queue must always be locked when reading the time (see
+        // `schedule_from`).
+        let mut scheduler_queue = self.scheduler_queue.lock().unwrap();
+        let now = self.time();
+        let time = deadline.into_time(now);
+        if now >= time {
+            return Err(SchedulingError::InvalidScheduledTime);
+        }
+
+        scheduler_queue.insert((time, origin_id), action);
+
+        Ok(event_key)
+    }
+
+    /// Schedules a periodically recurring event identified by its origin at a
+    /// future time.
+    pub(crate) fn schedule_periodic_event_from<M, F, T, S>(
+        &self,
+        deadline: impl Deadline,
+        period: Duration,
+        func: F,
+        arg: T,
+        address: impl Into<Address<M>>,
+        origin_id: usize,
+    ) -> Result<(), SchedulingError>
+    where
+        M: Model,
+        F: for<'a> InputFn<'a, M, T, S> + Clone,
+        T: Send + Clone + 'static,
+        S: Send + 'static,
+    {
+        if period.is_zero() {
+            return Err(SchedulingError::NullRepetitionPeriod);
+        }
+        let sender = address.into().0;
+        let action = Action::new(PeriodicAction::new(
+            || process_event(func, arg, sender),
+            period,
+        ));
+
+        // The scheduler queue must always be locked when reading the time (see
+        // `schedule_from`).
+        let mut scheduler_queue = self.scheduler_queue.lock().unwrap();
+        let now = self.time();
+        let time = deadline.into_time(now);
+        if now >= time {
+            return Err(SchedulingError::InvalidScheduledTime);
+        }
+
+        scheduler_queue.insert((time, origin_id), action);
+
+        Ok(())
+    }
+
+    /// Schedules a cancellable, periodically recurring event identified by its
+    /// origin at a future time and returns an event key.
+    pub(crate) fn schedule_keyed_periodic_event_from<M, F, T, S>(
+        &self,
+        deadline: impl Deadline,
+        period: Duration,
+        func: F,
+        arg: T,
+        address: impl Into<Address<M>>,
+        origin_id: usize,
+    ) -> Result<ActionKey, SchedulingError>
+    where
+        M: Model,
+        F: for<'a> InputFn<'a, M, T, S> + Clone,
+        T: Send + Clone + 'static,
+        S: Send + 'static,
+    {
+        if period.is_zero() {
+            return Err(SchedulingError::NullRepetitionPeriod);
+        }
+        let event_key = ActionKey::new();
+        let sender = address.into().0;
+        let action = Action::new(KeyedPeriodicAction::new(
+            |ek| send_keyed_event(ek, func, arg, sender),
+            period,
+            event_key.clone(),
+        ));
+
+        // The scheduler queue must always be locked when reading the time (see
+        // `schedule_from`).
+        let mut scheduler_queue = self.scheduler_queue.lock().unwrap();
+        let now = self.time();
+        let time = deadline.into_time(now);
+        if now >= time {
+            return Err(SchedulingError::InvalidScheduledTime);
+        }
+
+        scheduler_queue.insert((time, origin_id), action);
+
+        Ok(event_key)
+    }
+
+    /// Requests the simulation to stop when advancing to the next step.
+    pub(crate) fn halt(&mut self) {
+        self.is_halted.store(true, Ordering::Relaxed);
+    }
+}
+
+impl fmt::Debug for GlobalScheduler {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SchedulerInner")
+            .field("time", &self.time())
+            .finish_non_exhaustive()
+    }
+}
+
+/// Trait abstracting over the inner type of an action.
+pub(crate) trait ActionInner: Send + 'static {
+    /// Reports whether the action was cancelled.
+    fn is_cancelled(&self) -> bool;
+
+    /// If this is a periodic action, returns a boxed clone of this action and
+    /// its repetition period; otherwise returns `None`.
+    fn next(&self) -> Option<(Box<dyn ActionInner>, Duration)>;
+
+    /// Returns a boxed future that performs the action.
+    fn into_future(self: Box<Self>) -> Pin<Box<dyn Future<Output = ()> + Send>>;
+
+    /// Spawns the future that performs the action onto the provided executor.
+    ///
+    /// This method is typically more efficient that spawning the boxed future
+    /// from `into_future` since it can directly spawn the unboxed future.
+    fn spawn_and_forget(self: Box<Self>, executor: &Executor);
+}
+
+/// An object that can be converted to a future performing a single
+/// non-cancellable action.
+///
+/// Note that this particular action is in fact already a future: since the
+/// future cannot be cancelled and the action does not need to be cloned,
+/// there is no need to defer the construction of the future. This makes
+/// `into_future` a trivial cast, which saves a boxing operation.
+#[pin_project]
+pub(crate) struct OnceAction<F> {
+    #[pin]
+    fut: F,
+}
+
+impl<F> OnceAction<F>
+where
+    F: Future<Output = ()> + Send + 'static,
+{
+    /// Constructs a new `OnceAction`.
+    pub(crate) fn new(fut: F) -> Self {
+        OnceAction { fut }
+    }
+}
+
+impl<F> Future for OnceAction<F>
+where
+    F: Future,
+{
+    type Output = F::Output;
+
+    #[inline(always)]
+    fn poll(self: std::pin::Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.project().fut.poll(cx)
+    }
+}
+
+impl<F> ActionInner for OnceAction<F>
+where
+    F: Future<Output = ()> + Send + 'static,
+{
+    fn is_cancelled(&self) -> bool {
+        false
+    }
+    fn next(&self) -> Option<(Box<dyn ActionInner>, Duration)> {
+        None
+    }
+    fn into_future(self: Box<Self>) -> Pin<Box<dyn Future<Output = ()> + Send>> {
+        // No need for boxing, type coercion is enough here.
+        Box::into_pin(self)
+    }
+    fn spawn_and_forget(self: Box<Self>, executor: &Executor) {
+        executor.spawn_and_forget(*self);
+    }
+}
+
+/// An object that can be converted to a future performing a non-cancellable,
+/// periodic action.
+pub(crate) struct PeriodicAction<G, F>
+where
+    G: (FnOnce() -> F) + Clone + Send + 'static,
+    F: Future<Output = ()> + Send + 'static,
+{
+    /// A clonable generator for the associated future.
+    gen: G,
+    /// The action repetition period.
+    period: Duration,
+}
+
+impl<G, F> PeriodicAction<G, F>
+where
+    G: (FnOnce() -> F) + Clone + Send + 'static,
+    F: Future<Output = ()> + Send + 'static,
+{
+    /// Constructs a new `PeriodicAction`.
+    pub(crate) fn new(gen: G, period: Duration) -> Self {
+        Self { gen, period }
+    }
+}
+
+impl<G, F> ActionInner for PeriodicAction<G, F>
+where
+    G: (FnOnce() -> F) + Clone + Send + 'static,
+    F: Future<Output = ()> + Send + 'static,
+{
+    fn is_cancelled(&self) -> bool {
+        false
+    }
+    fn next(&self) -> Option<(Box<dyn ActionInner>, Duration)> {
+        let event = Box::new(Self::new(self.gen.clone(), self.period));
+
+        Some((event, self.period))
+    }
+    fn into_future(self: Box<Self>) -> Pin<Box<dyn Future<Output = ()> + Send>> {
+        Box::pin((self.gen)())
+    }
+    fn spawn_and_forget(self: Box<Self>, executor: &Executor) {
+        executor.spawn_and_forget((self.gen)());
+    }
+}
+
+/// An object that can be converted to a future performing a single, cancellable
+/// action.
+pub(crate) struct KeyedOnceAction<G, F>
+where
+    G: (FnOnce(ActionKey) -> F) + Send + 'static,
+    F: Future<Output = ()> + Send + 'static,
+{
+    /// A generator for the associated future.
+    gen: G,
+    /// The event cancellation key.
+    event_key: ActionKey,
+}
+
+impl<G, F> KeyedOnceAction<G, F>
+where
+    G: (FnOnce(ActionKey) -> F) + Send + 'static,
+    F: Future<Output = ()> + Send + 'static,
+{
+    /// Constructs a new `KeyedOnceAction`.
+    pub(crate) fn new(gen: G, event_key: ActionKey) -> Self {
+        Self { gen, event_key }
+    }
+}
+
+impl<G, F> ActionInner for KeyedOnceAction<G, F>
+where
+    G: (FnOnce(ActionKey) -> F) + Send + 'static,
+    F: Future<Output = ()> + Send + 'static,
+{
+    fn is_cancelled(&self) -> bool {
+        self.event_key.is_cancelled()
+    }
+    fn next(&self) -> Option<(Box<dyn ActionInner>, Duration)> {
+        None
+    }
+    fn into_future(self: Box<Self>) -> Pin<Box<dyn Future<Output = ()> + Send>> {
+        Box::pin((self.gen)(self.event_key))
+    }
+    fn spawn_and_forget(self: Box<Self>, executor: &Executor) {
+        executor.spawn_and_forget((self.gen)(self.event_key));
+    }
+}
+
+/// An object that can be converted to a future performing a periodic,
+/// cancellable action.
+pub(crate) struct KeyedPeriodicAction<G, F>
+where
+    G: (FnOnce(ActionKey) -> F) + Clone + Send + 'static,
+    F: Future<Output = ()> + Send + 'static,
+{
+    /// A clonable generator for associated future.
+    gen: G,
+    /// The repetition period.
+    period: Duration,
+    /// The event cancellation key.
+    event_key: ActionKey,
+}
+
+impl<G, F> KeyedPeriodicAction<G, F>
+where
+    G: (FnOnce(ActionKey) -> F) + Clone + Send + 'static,
+    F: Future<Output = ()> + Send + 'static,
+{
+    /// Constructs a new `KeyedPeriodicAction`.
+    pub(crate) fn new(gen: G, period: Duration, event_key: ActionKey) -> Self {
+        Self {
+            gen,
+            period,
+            event_key,
+        }
+    }
+}
+
+impl<G, F> ActionInner for KeyedPeriodicAction<G, F>
+where
+    G: (FnOnce(ActionKey) -> F) + Clone + Send + 'static,
+    F: Future<Output = ()> + Send + 'static,
+{
+    fn is_cancelled(&self) -> bool {
+        self.event_key.is_cancelled()
+    }
+    fn next(&self) -> Option<(Box<dyn ActionInner>, Duration)> {
+        let event = Box::new(Self::new(
+            self.gen.clone(),
+            self.period,
+            self.event_key.clone(),
+        ));
+
+        Some((event, self.period))
+    }
+    fn into_future(self: Box<Self>) -> Pin<Box<dyn Future<Output = ()> + Send>> {
+        Box::pin((self.gen)(self.event_key))
+    }
+    fn spawn_and_forget(self: Box<Self>, executor: &Executor) {
+        executor.spawn_and_forget((self.gen)(self.event_key));
+    }
+}
+
+/// Asynchronously sends a non-cancellable event to a model input.
+pub(crate) async fn process_event<M, F, T, S>(func: F, arg: T, sender: Sender<M>)
+where
+    M: Model,
+    F: for<'a> InputFn<'a, M, T, S>,
+    T: Send + 'static,
+{
+    let _ = sender
+        .send(
+            move |model: &mut M,
+                  scheduler,
+                  recycle_box: RecycleBox<()>|
+                  -> RecycleBox<dyn Future<Output = ()> + Send + '_> {
+                let fut = func.call(model, arg, scheduler);
+
+                coerce_box!(RecycleBox::recycle(recycle_box, fut))
+            },
+        )
+        .await;
+}
+
+/// Asynchronously sends a cancellable event to a model input.
+pub(crate) async fn send_keyed_event<M, F, T, S>(
+    event_key: ActionKey,
+    func: F,
+    arg: T,
+    sender: Sender<M>,
+) where
+    M: Model,
+    F: for<'a> InputFn<'a, M, T, S>,
+    T: Send + Clone + 'static,
+{
+    let _ = sender
+        .send(
+            move |model: &mut M,
+                  scheduler,
+                  recycle_box: RecycleBox<()>|
+                  -> RecycleBox<dyn Future<Output = ()> + Send + '_> {
+                let fut = async move {
+                    // Only perform the call if the event wasn't cancelled.
+                    if !event_key.is_cancelled() {
+                        func.call(model, arg, scheduler).await;
+                    }
+                };
+
+                coerce_box!(RecycleBox::recycle(recycle_box, fut))
+            },
+        )
+        .await;
+}
+
+#[cfg(all(test, not(nexosim_loom)))]
+impl GlobalScheduler {
+    /// Creates a dummy scheduler for testing purposes.
+    pub(crate) fn new_dummy() -> Self {
+        let dummy_priority_queue = Arc::new(Mutex::new(PriorityQueue::new()));
+        let dummy_time = SyncCell::new(TearableAtomicTime::new(MonotonicTime::EPOCH)).reader();
+        let dummy_halter = Arc::new(AtomicBool::new(false));
+        GlobalScheduler::new(dummy_priority_queue, dummy_time, dummy_halter)
+    }
+}

nexosim/src/simulation/sim_init.rs

@@ -0,0 +1,204 @@
+use std::fmt;
+use std::sync::atomic::AtomicBool;
+use std::sync::{Arc, Mutex};
+use std::time::Duration;
+
+use crate::channel::ChannelObserver;
+use crate::executor::{Executor, SimulationContext};
+use crate::model::ProtoModel;
+use crate::time::{AtomicTime, Clock, MonotonicTime, NoClock, SyncStatus, TearableAtomicTime};
+use crate::util::priority_queue::PriorityQueue;
+use crate::util::sync_cell::SyncCell;
+
+use super::{
+    add_model, ExecutionError, GlobalScheduler, Mailbox, Scheduler, SchedulerQueue, Signal,
+    Simulation,
+};
+
+/// Builder for a multi-threaded, discrete-event simulation.
+pub struct SimInit {
+    executor: Executor,
+    scheduler_queue: Arc<Mutex<SchedulerQueue>>,
+    time: AtomicTime,
+    is_halted: Arc<AtomicBool>,
+    clock: Box<dyn Clock + 'static>,
+    clock_tolerance: Option<Duration>,
+    timeout: Duration,
+    observers: Vec<(String, Box<dyn ChannelObserver>)>,
+    abort_signal: Signal,
+    model_names: Vec<String>,
+}
+
+impl SimInit {
+    /// Creates a builder for a multithreaded simulation running on all
+    /// available logical threads.
+    pub fn new() -> Self {
+        Self::with_num_threads(num_cpus::get())
+    }
+
+    /// Creates a builder for a simulation running on the specified number of
+    /// threads.
+    ///
+    /// Note that the number of worker threads is automatically constrained to
+    /// be between 1 and `usize::BITS` (inclusive). It is always set to 1 on
+    /// `wasm` targets.
+    pub fn with_num_threads(num_threads: usize) -> Self {
+        let num_threads = if cfg!(target_family = "wasm") {
+            1
+        } else {
+            num_threads.clamp(1, usize::BITS as usize)
+        };
+        let time = SyncCell::new(TearableAtomicTime::new(MonotonicTime::EPOCH));
+        let simulation_context = SimulationContext {
+            #[cfg(feature = "tracing")]
+            time_reader: time.reader(),
+        };
+
+        let abort_signal = Signal::new();
+        let executor = if num_threads == 1 {
+            Executor::new_single_threaded(simulation_context, abort_signal.clone())
+        } else {
+            Executor::new_multi_threaded(num_threads, simulation_context, abort_signal.clone())
+        };
+
+        Self {
+            executor,
+            scheduler_queue: Arc::new(Mutex::new(PriorityQueue::new())),
+            time,
+            is_halted: Arc::new(AtomicBool::new(false)),
+            clock: Box::new(NoClock::new()),
+            clock_tolerance: None,
+            timeout: Duration::ZERO,
+            observers: Vec::new(),
+            abort_signal,
+            model_names: Vec::new(),
+        }
+    }
+
+    /// Adds a model and its mailbox to the simulation bench.
+    ///
+    /// The `name` argument needs not be unique. The use of the dot character in
+    /// the name is possible but discouraged as it can cause confusion with the
+    /// fully qualified name of a submodel. If an empty string is provided, it
+    /// is replaced by the string `<unknown>`.
+    pub fn add_model<P: ProtoModel>(
+        mut self,
+        model: P,
+        mailbox: Mailbox<P::Model>,
+        name: impl Into<String>,
+    ) -> Self {
+        let mut name = name.into();
+        if name.is_empty() {
+            name = String::from("<unknown>");
+        };
+        self.observers
+            .push((name.clone(), Box::new(mailbox.0.observer())));
+        let scheduler = GlobalScheduler::new(
+            self.scheduler_queue.clone(),
+            self.time.reader(),
+            self.is_halted.clone(),
+        );
+
+        add_model(
+            model,
+            mailbox,
+            name,
+            scheduler,
+            &self.executor,
+            &self.abort_signal,
+            &mut self.model_names,
+        );
+
+        self
+    }
+
+    /// Synchronizes the simulation with the provided [`Clock`].
+    ///
+    /// If the clock isn't explicitly set then the default [`NoClock`] is used,
+    /// resulting in the simulation running as fast as possible.
+    pub fn set_clock(mut self, clock: impl Clock + 'static) -> Self {
+        self.clock = Box::new(clock);
+
+        self
+    }
+
+    /// Specifies a tolerance for clock synchronization.
+    ///
+    /// When a clock synchronization tolerance is set, then any report of
+    /// synchronization loss by [`Clock::synchronize`] that exceeds the
+    /// specified tolerance will trigger an [`ExecutionError::OutOfSync`] error.
+    pub fn set_clock_tolerance(mut self, tolerance: Duration) -> Self {
+        self.clock_tolerance = Some(tolerance);
+
+        self
+    }
+
+    /// Sets a timeout for the call to [`SimInit::init`] and for any subsequent
+    /// simulation step.
+    ///
+    /// The timeout corresponds to the maximum wall clock time allocated for the
+    /// completion of a single simulation step before an
+    /// [`ExecutionError::Timeout`] error is raised.
+    ///
+    /// A null duration disables the timeout, which is the default behavior.
+    ///
+    /// See also [`Simulation::set_timeout`].
+    #[cfg(not(target_family = "wasm"))]
+    pub fn set_timeout(mut self, timeout: Duration) -> Self {
+        self.timeout = timeout;
+
+        self
+    }
+
+    /// Builds a simulation initialized at the specified simulation time,
+    /// executing the [`Model::init`](crate::model::Model::init) method on all
+    /// model initializers.
+    ///
+    /// The simulation object and its associated scheduler are returned upon
+    /// success.
+    pub fn init(
+        mut self,
+        start_time: MonotonicTime,
+    ) -> Result<(Simulation, Scheduler), ExecutionError> {
+        self.time.write(start_time);
+        if let SyncStatus::OutOfSync(lag) = self.clock.synchronize(start_time) {
+            if let Some(tolerance) = &self.clock_tolerance {
+                if &lag > tolerance {
+                    return Err(ExecutionError::OutOfSync(lag));
+                }
+            }
+        }
+
+        let scheduler = Scheduler::new(
+            self.scheduler_queue.clone(),
+            self.time.reader(),
+            self.is_halted.clone(),
+        );
+        let mut simulation = Simulation::new(
+            self.executor,
+            self.scheduler_queue,
+            self.time,
+            self.clock,
+            self.clock_tolerance,
+            self.timeout,
+            self.observers,
+            self.model_names,
+            self.is_halted,
+        );
+        simulation.run()?;
+
+        Ok((simulation, scheduler))
+    }
+}
+
+impl Default for SimInit {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl fmt::Debug for SimInit {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SimInit").finish_non_exhaustive()
+    }
+}

nexosim/src/time.rs

@@ -0,0 +1,81 @@
+//! Simulation time and clocks.
+//!
+//! This module provides most notably:
+//!
+//! * [`MonotonicTime`]: a monotonic timestamp based on the [TAI] time standard,
+//! * [`Clock`]: a trait for types that can synchronize a simulation,
+//!   implemented for instance by [`SystemClock`] and [`AutoSystemClock`].
+//!
+//! [TAI]: https://en.wikipedia.org/wiki/International_Atomic_Time
+//!
+//!
+//! # Examples
+//!
+//! An alarm clock model that prints a message when the simulation time reaches
+//! the specified timestamp.
+//!
+//! ```
+//! use nexosim::model::{Context, Model};
+//! use nexosim::time::MonotonicTime;
+//!
+//! // An alarm clock model.
+//! pub struct AlarmClock {
+//!     msg: String
+//! }
+//!
+//! impl AlarmClock {
+//!     // Creates a new alarm clock.
+//!     pub fn new(msg: String) -> Self {
+//!         Self { msg }
+//!     }
+//!
+//!     // Sets an alarm [input port].
+//!     pub fn set(&mut self, setting: MonotonicTime, cx: &mut Context<Self>) {
+//!         if cx.schedule_event(setting, Self::ring, ()).is_err() {
+//!             println!("The alarm clock can only be set for a future time");
+//!         }
+//!     }
+//!
+//!     // Rings the alarm [private input port].
+//!     fn ring(&mut self) {
+//!         println!("{}", self.msg);
+//!     }
+//! }
+//!
+//! impl Model for AlarmClock {}
+//! ```
+
+mod clock;
+mod monotonic_time;
+
+pub use tai_time::MonotonicTime;
+
+pub use clock::{AutoSystemClock, Clock, NoClock, SyncStatus, SystemClock};
+pub(crate) use monotonic_time::TearableAtomicTime;
+
+pub(crate) type AtomicTime = crate::util::sync_cell::SyncCell<TearableAtomicTime>;
+pub(crate) type AtomicTimeReader = crate::util::sync_cell::SyncCellReader<TearableAtomicTime>;
+
+/// Trait abstracting over time-absolute and time-relative deadlines.
+///
+/// This trait is implemented by [`std::time::Duration`] and
+/// [`MonotonicTime`].
+pub trait Deadline {
+    /// Make this deadline into an absolute timestamp, using the provided
+    /// current time as a reference.
+    fn into_time(self, now: MonotonicTime) -> MonotonicTime;
+}
+
+impl Deadline for std::time::Duration {
+    #[inline(always)]
+    fn into_time(self, now: MonotonicTime) -> MonotonicTime {
+        now + self
+    }
+}
+
+impl Deadline for MonotonicTime {
+    #[inline(always)]
+    fn into_time(self, _: MonotonicTime) -> MonotonicTime {
+        self
+    }
+}

nexosim/src/time/clock.rs

@@ -1,25 +1,52 @@
 use std::time::{Duration, Instant, SystemTime};
 
+use tai_time::MonotonicClock;
+
 use crate::time::MonotonicTime;
 
 /// A type that can be used to synchronize a simulation.
 ///
-/// This trait abstract over the different types of clocks, such as
+/// This trait abstracts over different types of clocks, such as
 /// as-fast-as-possible and real-time clocks.
 ///
-/// A clock can be associated to a simulation at initialization time by calling
-/// [`SimInit::init_with_clock()`](crate::simulation::SimInit::init_with_clock).
+/// A clock can be associated to a simulation prior to initialization by calling
+/// [`SimInit::set_clock`](crate::simulation::SimInit::set_clock).
 pub trait Clock: Send {
     /// Blocks until the deadline.
     fn synchronize(&mut self, deadline: MonotonicTime) -> SyncStatus;
+
+    // Returns current (as of time of the call) sim time
+    fn now(&self) -> MonotonicTime;
+}
+
+impl<C: Clock + ?Sized> Clock for &mut C {
+    fn synchronize(&mut self, deadline: MonotonicTime) -> SyncStatus {
+        (**self).synchronize(deadline)
+    }
+
+    fn now(&self) -> MonotonicTime{
+        (**self).now()
+    }
+}
+
+impl<C: Clock + ?Sized> Clock for Box<C> {
+    fn synchronize(&mut self, deadline: MonotonicTime) -> SyncStatus {
+        (**self).synchronize(deadline)
+    }
+
+    fn now(&self) -> MonotonicTime{
+        (**self).now()
+    }
 }
 
 /// The current synchronization status of a clock.
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[must_use]
 pub enum SyncStatus {
     /// The clock is synchronized.
     Synchronized,
-    /// The clock is lagging behind by the specified offset.
+    /// The deadline has already elapsed and lags behind the current clock time
+    /// by the duration given in the payload.
     OutOfSync(Duration),
 }
 
@@ -42,6 +69,10 @@ impl Clock for NoClock {
     fn synchronize(&mut self, _: MonotonicTime) -> SyncStatus {
         SyncStatus::Synchronized
     }
+
+    fn now(&self) -> MonotonicTime{
+        MonotonicTime::new(0, 0).unwrap()
+    }
 }
 
 /// A real-time [`Clock`] based on the system's monotonic clock.
@@ -49,10 +80,7 @@ impl Clock for NoClock {
 /// This clock accepts an arbitrary reference time and remains synchronized with
 /// the system's monotonic clock.
 #[derive(Copy, Clone, Debug)]
-pub struct SystemClock {
-    wall_clock_ref: Instant,
-    simulation_ref: MonotonicTime,
-}
+pub struct SystemClock(MonotonicClock);
 
 impl SystemClock {
     /// Constructs a `SystemClock` with an offset between simulation clock and
@@ -66,10 +94,10 @@ impl SystemClock {
     /// ```
     /// use std::time::{Duration, Instant};
     ///
-    /// use asynchronix::simulation::SimInit;
-    /// use asynchronix::time::{MonotonicTime, SystemClock};
+    /// use nexosim::simulation::SimInit;
+    /// use nexosim::time::{MonotonicTime, SystemClock};
     ///
-    /// let t0 = MonotonicTime::new(1_234_567_890, 0);
+    /// let t0 = MonotonicTime::new(1_234_567_890, 0).unwrap();
     ///
     /// // Make the simulation start in 1s.
     /// let clock = SystemClock::from_instant(t0, Instant::now() + Duration::from_secs(1));
@@ -77,13 +105,14 @@ impl SystemClock {
     /// let simu = SimInit::new()
     /// //  .add_model(...)
     /// //  .add_model(...)
-    ///     .init_with_clock(t0, clock);
+    ///     .set_clock(clock)
+    ///     .init(t0);
     /// ```
     pub fn from_instant(simulation_ref: MonotonicTime, wall_clock_ref: Instant) -> Self {
-        Self {
-            wall_clock_ref,
+        Self(MonotonicClock::init_from_instant(
             simulation_ref,
-        }
+            wall_clock_ref,
+        ))
     }
 
     /// Constructs a `SystemClock` with an offset between simulation clock and
@@ -93,7 +122,7 @@ impl SystemClock {
     /// The provided reference time may lie in the past or in the future.
     ///
     /// Note that, even though the wall clock reference is specified with the
-    /// (non-monotonic) system clock, the [`synchronize()`](Clock::synchronize)
+    /// (non-monotonic) system clock, the [`synchronize`](Clock::synchronize)
     /// method will still use the system's _monotonic_ clock. This constructor
     /// makes a best-effort attempt at synchronizing the monotonic clock with
     /// the non-monotonic system clock _at construction time_, but this
@@ -106,10 +135,10 @@ impl SystemClock {
     /// ```
     /// use std::time::{Duration, UNIX_EPOCH};
     ///
-    /// use asynchronix::simulation::SimInit;
-    /// use asynchronix::time::{MonotonicTime, SystemClock};
+    /// use nexosim::simulation::SimInit;
+    /// use nexosim::time::{MonotonicTime, SystemClock};
     ///
-    /// let t0 = MonotonicTime::new(1_234_567_890, 0);
+    /// let t0 = MonotonicTime::new(1_234_567_890, 0).unwrap();
     ///
     /// // Make the simulation start at the next full second boundary.
     /// let now_secs = UNIX_EPOCH.elapsed().unwrap().as_secs();
@@ -120,58 +149,14 @@ impl SystemClock {
     /// let simu = SimInit::new()
     /// //  .add_model(...)
     /// //  .add_model(...)
-    ///     .init_with_clock(t0, clock);
+    ///     .set_clock(clock)
+    ///     .init(t0);
     /// ```
     pub fn from_system_time(simulation_ref: MonotonicTime, wall_clock_ref: SystemTime) -> Self {
-        // Select the best-correlated `Instant`/`SystemTime` pair from several
-        // samples to improve robustness towards possible thread suspension
-        // between the calls to `SystemTime::now()` and `Instant::now()`.
-        const SAMPLES: usize = 3;
-
-        let mut last_instant = Instant::now();
-        let mut min_delta = Duration::MAX;
-        let mut ref_time = None;
-
-        // Select the best-correlated instant/date pair.
-        for _ in 0..SAMPLES {
-            // The inner loop is to work around monotonic clock platform bugs
-            // that may cause `checked_duration_since` to fail.
-            let (date, instant, delta) = loop {
-                let date = SystemTime::now();
-                let instant = Instant::now();
-                let delta = instant.checked_duration_since(last_instant);
-                last_instant = instant;
-
-                if let Some(delta) = delta {
-                    break (date, instant, delta);
-                }
-            };
-
-            // Store the current instant/date if the time elapsed since the last
-            // measurement is shorter than the previous candidate.
-            if min_delta > delta {
-                min_delta = delta;
-                ref_time = Some((instant, date));
-            }
-        }
-
-        // Set the selected instant/date as the wall clock reference and adjust
-        // the simulation reference accordingly.
-        let (instant_ref, date_ref) = ref_time.unwrap();
-        let simulation_ref = if date_ref > wall_clock_ref {
-            let correction = date_ref.duration_since(wall_clock_ref).unwrap();
-
-            simulation_ref + correction
-        } else {
-            let correction = wall_clock_ref.duration_since(date_ref).unwrap();
-
-            simulation_ref - correction
-        };
-
-        Self {
-            wall_clock_ref: instant_ref,
+        Self(MonotonicClock::init_from_system_time(
             simulation_ref,
-        }
+            wall_clock_ref,
+        ))
     }
 }
 
@@ -179,22 +164,18 @@ impl Clock for SystemClock {
     /// Blocks until the system time corresponds to the specified simulation
     /// time.
     fn synchronize(&mut self, deadline: MonotonicTime) -> SyncStatus {
-        let target_time = if deadline >= self.simulation_ref {
-            self.wall_clock_ref + deadline.duration_since(self.simulation_ref)
-        } else {
-            self.wall_clock_ref - self.simulation_ref.duration_since(deadline)
-        };
+        let now = self.0.now();
+        if now <= deadline {
+            spin_sleep::sleep(deadline.duration_since(now));
 
-        let now = Instant::now();
-
-        match target_time.checked_duration_since(now) {
-            Some(sleep_duration) => {
-                spin_sleep::sleep(sleep_duration);
-
-                SyncStatus::Synchronized
-            }
-            None => SyncStatus::OutOfSync(now.duration_since(target_time)),
+            return SyncStatus::Synchronized;
         }
+
+        SyncStatus::OutOfSync(now.duration_since(deadline))
+    }
+
+    fn now(&self) -> MonotonicTime{
+        self.0.now()
     }
 }
 
@@ -202,8 +183,8 @@ impl Clock for SystemClock {
 /// monotonic clock.
 ///
 /// This clock is similar to [`SystemClock`] except that the first call to
-/// [`synchronize()`](Clock::synchronize) never blocks and implicitly defines
-/// the reference time. In other words, the clock starts running on its first
+/// [`synchronize`](Clock::synchronize) never blocks and implicitly defines the
+/// reference time. In other words, the clock starts running on its first
 /// invocation.
 #[derive(Copy, Clone, Debug, Default)]
 pub struct AutoSystemClock {
@@ -232,4 +213,35 @@ impl Clock for AutoSystemClock {
             Some(clock) => clock.synchronize(deadline),
         }
     }
+
+    fn now(&self) -> MonotonicTime {
+        // TODO: how to avoid panic? self is not mut
+        self.inner.unwrap().now()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn smoke_system_clock() {
+        let t0 = MonotonicTime::EPOCH;
+        const TOLERANCE: f64 = 0.0005; // [s]
+
+        let now = Instant::now();
+        let mut clock = SystemClock::from_instant(t0, now);
+        let t1 = t0 + Duration::from_millis(200);
+        assert_eq!(clock.synchronize(t1), SyncStatus::Synchronized);
+        let elapsed = now.elapsed().as_secs_f64();
+        let dt = t1.duration_since(t0).as_secs_f64();
+
+        assert!(
+            (dt - elapsed) <= TOLERANCE,
+            "Expected t = {:.6}s +/- {:.6}s, measured t = {:.6}s",
+            dt,
+            TOLERANCE,
+            elapsed,
+        );
+    }
 }