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Make it possible to cancel current-time events

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This is a pretty large patch that impacts the API.

Until now, it was not possible to cancel events that were scheduled for
the current simulation time slice, making it necessary for the user to
use complex workarounds (see former version of the espresso machine
example).

The new implementation makes this possible but the generation of a key
associated to an event has now a non-negligible cost (basicaly it
creates three references to an Arc). For this reason, the API now
defaults to NOT creating a key, and new methods were added for
situations when the event may need to be cancelled and a key is
necessary.

See the much simplified implementation of the espresso machine example
for a motivating case.
This commit is contained in:
Serge Barral
2023-07-19 19:01:37 +02:00
parent 045dea509c
commit f458377308
9 changed files with 535 additions and 199 deletions
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199
asynchronix/src/simulation.rs
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@ -73,7 +73,7 @@
//!
//! At the moment, Asynchronix is unfortunately not able to discriminate between
//! such pathological deadlocks and the "expected" deadlock that occurs when all
//! tasks in a given time slice have completed and all models are starved on an
//! 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
@ -91,8 +91,8 @@
//! 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:
//! [`Simulation::send_event()`] with a closure that connects or disconnects a
//! port, such as:
//!
//! ```
//! # use asynchronix::model::{Model, Output};
@ -129,15 +129,15 @@ pub use sim_init::SimInit;
use std::error::Error;
use std::fmt;
use std::future::Future;
use std::sync::{Arc, Mutex};
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, CancellationError, MonotonicTime, TearableAtomicTime};
use crate::time::{ScheduledTimeError, SchedulerKey, SchedulerQueue};
use crate::time::{self, MonotonicTime, TearableAtomicTime};
use crate::time::{EventKey, ScheduledTimeError, SchedulerQueue};
use crate::util::futures::SeqFuture;
use crate::util::slot;
use crate::util::sync_cell::SyncCell;
@ -164,9 +164,9 @@ use crate::util::sync_cell::SyncCell;
/// the case of queries, the response is returned.
///
/// Events can also be scheduled at a future simulation time using
/// [`schedule_in()`](Simulation::schedule_in) or
/// [`schedule_at()`](Simulation::schedule_at). These methods queue an event
/// without blocking.
/// [`schedule_event_in()`](Simulation::schedule_event_in) or
/// [`schedule_event_at()`](Simulation::schedule_event_at). These methods queue
/// an event without blocking.
///
/// Finally, the [`Simulation`] instance manages simulation time. Calling
/// [`step()`](Simulation::step) will increment simulation time until that of
@ -201,20 +201,20 @@ impl Simulation {
self.time.read()
}
/// Advances simulation time to that of the next scheduled task, processing
/// that task as well as all other tasks scheduled for the same time.
/// Advances simulation time to that of the next scheduled event, processing
/// that event as well as all other event scheduled for the same time.
///
/// This method may block. Once it returns, it is guaranteed that all newly
/// processed tasks (if any) have completed.
/// processed event (if any) have completed.
pub fn step(&mut self) {
self.step_to_next_bounded(MonotonicTime::MAX);
}
/// Iteratively advances the simulation time by the specified duration and
/// processes all tasks scheduled up to the target time.
/// processes all events scheduled up to the target time.
///
/// This method may block. Once it returns, it is guaranteed that (i) all
/// tasks scheduled up to the specified target time have completed and (ii)
/// events scheduled up to the specified target time have completed and (ii)
/// the final simulation time has been incremented by the specified
/// duration.
pub fn step_by(&mut self, duration: Duration) {
@ -223,11 +223,11 @@ impl Simulation {
self.step_until_unchecked(target_time);
}
/// Iteratively advances the simulation time and processes all tasks
/// Iteratively advances the simulation time and processes all events
/// scheduled up to the specified target time.
///
/// This method may block. Once it returns, it is guaranteed that (i) all
/// tasks scheduled up to the specified target time have completed and (ii)
/// events scheduled up to the specified target time have completed and (ii)
/// the final simulation time matches the target time.
pub fn step_until(&mut self, target_time: MonotonicTime) -> Result<(), ScheduledTimeError<()>> {
if self.time.read() >= target_time {
@ -244,13 +244,13 @@ impl Simulation {
///
/// Events scheduled for the same time and targeting the same model are
/// guaranteed to be processed according to the scheduling order.
pub fn schedule_in<M, F, T, S>(
pub fn schedule_event_in<M, F, T, S>(
&mut self,
duration: Duration,
func: F,
arg: T,
address: impl Into<Address<M>>,
) -> Result<SchedulerKey, ScheduledTimeError<T>>
) -> Result<(), ScheduledTimeError<T>>
where
M: Model,
F: for<'a> InputFn<'a, M, T, S>,
@ -261,7 +261,36 @@ impl Simulation {
}
let time = self.time.read() + duration;
let schedule_key = time::schedule_event_at_unchecked(
time::schedule_event_at_unchecked(time, func, arg, address.into().0, &self.scheduler_queue);
Ok(())
}
/// Schedules an event at the lapse of the specified duration and returns an
/// event key.
///
/// An error is returned if the specified duration 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_event_in<M, F, T, S>(
&mut self,
duration: Duration,
func: F,
arg: T,
address: impl Into<Address<M>>,
) -> Result<EventKey, ScheduledTimeError<T>>
where
M: Model,
F: for<'a> InputFn<'a, M, T, S>,
T: Send + Clone + 'static,
{
if duration.is_zero() {
return Err(ScheduledTimeError(arg));
}
let time = self.time.read() + duration;
let event_key = time::schedule_keyed_event_at_unchecked(
time,
func,
arg,
@ -269,7 +298,7 @@ impl Simulation {
&self.scheduler_queue,
);
Ok(schedule_key)
Ok(event_key)
}
/// Schedules an event at a future time.
@ -279,13 +308,13 @@ impl Simulation {
///
/// Events scheduled for the same time and targeting the same model are
/// guaranteed to be processed according to the scheduling order.
pub fn schedule_at<M, F, T, S>(
pub fn schedule_event_at<M, F, T, S>(
&mut self,
time: MonotonicTime,
func: F,
arg: T,
address: impl Into<Address<M>>,
) -> Result<SchedulerKey, ScheduledTimeError<T>>
) -> Result<(), ScheduledTimeError<T>>
where
M: Model,
F: for<'a> InputFn<'a, M, T, S>,
@ -294,7 +323,34 @@ impl Simulation {
if self.time.read() >= time {
return Err(ScheduledTimeError(arg));
}
let schedule_key = time::schedule_event_at_unchecked(
time::schedule_event_at_unchecked(time, func, arg, address.into().0, &self.scheduler_queue);
Ok(())
}
/// Schedules an 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_at<M, F, T, S>(
&mut self,
time: MonotonicTime,
func: F,
arg: T,
address: impl Into<Address<M>>,
) -> Result<EventKey, ScheduledTimeError<T>>
where
M: Model,
F: for<'a> InputFn<'a, M, T, S>,
T: Send + Clone + 'static,
{
if self.time.read() >= time {
return Err(ScheduledTimeError(arg));
}
let event_key = time::schedule_keyed_event_at_unchecked(
time,
func,
arg,
@ -302,16 +358,7 @@ impl Simulation {
&self.scheduler_queue,
);
Ok(schedule_key)
}
/// Cancels an event with a scheduled time in the future of the current
/// simulation time.
///
/// If the corresponding event was already executed, or if it is scheduled
/// for the current simulation time, an error is returned.
pub fn cancel(&self, scheduler_key: SchedulerKey) -> Result<(), CancellationError> {
time::cancel_scheduled(scheduler_key, &self.scheduler_queue)
Ok(event_key)
}
/// Sends and processes an event, blocking until completion.
@ -387,72 +434,84 @@ impl Simulation {
reply_reader.try_read().map_err(|_| QueryError {})
}
/// Advances simulation time to that of the next scheduled task if its
/// Advances simulation time to that of the next scheduled event if its
/// scheduling time does not exceed the specified bound, processing that
/// task as well as all other tasks scheduled for the same time.
/// event as well as all other events scheduled for the same time.
///
/// If at least one task was found that satisfied the time bound, the
/// 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> {
let mut scheduler_queue = self.scheduler_queue.lock().unwrap();
let mut current_key = match scheduler_queue.peek_key() {
Some(&k) if k.0 <= upper_time_bound => k,
_ => return None,
// Closure returning the next key which time stamp is no older than the
// upper bound, if any. Cancelled events are discarded.
let get_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,
}
}
};
// Set the simulation time to that of the next scheduled task
// Move to the next scheduled time.
let mut scheduler_queue = self.scheduler_queue.lock().unwrap();
let mut current_key = get_next_key(&mut scheduler_queue)?;
self.time.write(current_key.0);
loop {
let task = scheduler_queue.pull().unwrap().1;
let event = scheduler_queue.pull().unwrap().1;
let mut next_key = scheduler_queue.peek_key();
if next_key != Some(&current_key) {
// Since there are no other tasks targeting the same mailbox
// and the same time, the task is spawned immediately.
self.executor.spawn_and_forget(Box::into_pin(task));
let mut next_key = get_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.
self.executor.spawn_and_forget(Box::into_pin(event));
} else {
// To ensure that their relative order of execution is
// preserved, all tasks targeting the same mailbox are
// concatenated into a single future.
let mut task_sequence = SeqFuture::new();
// preserved, all event targeting the same mailbox are executed
// sequentially within a single compound future.
let mut event_sequence = SeqFuture::new();
task_sequence.push(Box::into_pin(task));
event_sequence.push(Box::into_pin(event));
loop {
let task = scheduler_queue.pull().unwrap().1;
task_sequence.push(Box::into_pin(task));
next_key = scheduler_queue.peek_key();
if next_key != Some(&current_key) {
let event = scheduler_queue.pull().unwrap().1;
event_sequence.push(Box::into_pin(event));
next_key = get_next_key(&mut scheduler_queue);
if next_key != Some(current_key) {
break;
}
}
// Spawn a parent task that sequentially polls all sub-tasks.
self.executor.spawn_and_forget(task_sequence);
// Spawn a parent event that sequentially polls all events
// targeting the same mailbox.
self.executor.spawn_and_forget(event_sequence);
}
match next_key {
// If the next task is scheduled at the same time, update the key and continue.
Some(k) if k.0 == current_key.0 => {
current_key = *k;
}
// Otherwise wait until all tasks have completed and return.
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 unlocked.
drop(scheduler_queue); // make sure the queue's mutex is released.
self.executor.run();
return Some(current_key.0);
}
}
};
}
}
/// Iteratively advances simulation time and processes all tasks scheduled
/// 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 tasks scheduled up
/// to the specified target time have completed and (ii) the final
/// 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
@ -462,7 +521,7 @@ impl Simulation {
match self.step_to_next_bounded(target_time) {
// The target time was reached exactly.
Some(t) if t == target_time => return,
// No tasks are scheduled before or at the target time.
// No events are scheduled before or at the target time.
None => {
// Update the simulation time.
self.time.write(target_time);