refining what is what in stores

mission_rust/src/fsrc/datasets/mod.rs

@@ -115,7 +115,7 @@ impl<T: Clone + Default + 'static> ReferencedDataset<T> {
             }
             Some(set) => set,
         };
-        // let's recheck that owner.get_set did not lie about the type_id
+        // let's recheck that owner.get_set() did not lie about the type_id
         if let Some(other_data) = other_set.get_actual_data().downcast_ref::<T>() {
             self.actual_data = Some(other_data);
         } else {

mission_rust/src/fsrc/store.rs

@@ -1,36 +1,71 @@
+use core::slice::SliceIndex;
+
 use crate::check_global_threading_available;
 
-struct Store{
-    mutex: crate::fsrc::mutex::RawMutex
-}
-
 trait StoreBackend {
-
+    fn free_slot(&mut self, length: usize) -> Option<*mut [u8]>;
 }
 
-struct StoreAccessor {
-    mutex: crate::fsrc::mutex::RawMutex
+struct Store<'a> {
+    mutex: crate::fsrc::mutex::RawMutex,
+    backend: &'a mut dyn StoreBackend,
 }
 
-impl Store {
-    pub fn get_accessor(&self) -> StoreAccessor {
+impl<'a> Store<'a> {
+    pub fn accessor(&mut self) -> StoreAccessor {
         check_global_threading_available!();
-        StoreAccessor{mutex: self.mutex.clone()}
+        // holy shit, this is really unsafe, even for us:
+        // we cast away the lifetime
+        // this is safe as we only do it in threading
+        // and the Accessor will only use it while still in threading
+        // (the accessor is a smart pointer refusing to be smart outside
+        // of threading)
+        let static_pointer = unsafe { core::mem::transmute::<*mut Store<'a>, *mut Store<'static>>(self) };
+        StoreAccessor {
+            store: static_pointer,
+        }
+    }
+
+    fn free_slot(&mut self, length: usize) -> Result<StoreSlot, ()> {
+        if let Ok(_guard) = self.mutex.take() {
+            if let Some(data) = self.backend.free_slot(length){
+                Ok(StoreSlot { data: data })
+            } else {
+                Err(())
+            }
+        } else {
+            Err(())
+        }
     }
 }
 
-struct StoreSlot{
-    data: *mut [u8]
+// A smart pointer to a Store protecting insane (static) pointer usage
+// only works during threading, panics otherwise
+struct StoreAccessor {
+    store: *mut Store<'static>,
+}
+
+impl StoreAccessor {
+    fn free_slot(&self, length: usize) -> Result<StoreSlot, ()> {
+        check_global_threading_available!();
+        unsafe { (*self.store).free_slot(length) }
+    }
+}
+
+struct StoreSlot {
+    data: *mut [u8],
 }
 
 impl StoreSlot {
-    pub fn get_data(&self) -> &mut [u8] {
+    pub fn get<I>(&self, index: I) -> &mut [u8] 
+    where I: SliceIndex<u8>
+     {
         check_global_threading_available!();
-        unsafe{&mut (*self.data)}
+        unsafe { &mut (*self.data) }
     }
 
-    pub fn get_all_data(&self) -> &mut [u8] {
+    pub fn get_all(&self) -> &mut [u8] {
         check_global_threading_available!();
-        unsafe{&mut (*self.data)}
+        unsafe { &mut (*self.data) }
     }
 }