zephyr: work: Generalize Work pointer type

First step in generalizing the worker type.  Place the inner pointer
type into a trait, and allow the work methods to work on pointers of
that type.

This continues to work the same as before with `Pin<Arc<Work<T>>>`.  It
needs a bit more massaging to be able to work with static pointers,
namely that the constructor has to be able to be static, and as such,
the initialization can't happen until it has been pinned down.  This
will likely change the "new" API.

Signed-off-by: David Brown <david.brown@linaro.org>

Author: d3zd3z

samples/bench/src/lib.rs

@@ -583,7 +583,7 @@ impl Simple {
 
     fn run(&self, workers: usize, iterations: usize) {
         // printkln!("Running Simple");
-        let main = Work::new(SimpleMain::new(workers * iterations, self.workq));
+        let main: Pin<Arc<Work<_>>> = Work::new(SimpleMain::new(workers * iterations, self.workq));
 
         let children: VecDeque<_> = (0..workers)
             .map(|n| Work::new(SimpleWorker::new(main.clone(), self.workq, n)))

zephyr/src/work.rs

@@ -331,24 +331,6 @@ impl SubmitResult {
     }
 }
 
-/*
-pub trait Queueable: Send + Sync {
-    fn as_ptr(&self) -> *const ();
-}
-
-impl<T: Send + Sync> Queueable for Arc<T> {
-    fn as_ptr(&self) -> *const () {
-        todo!()
-    }
-}
-
-impl<T: Send + Sync> Queueable for &'static T {
-    fn as_ptr(&self) -> *const () {
-        todo!()
-    }
-}
-*/
-
 /// A simple action that just does something with its data.
 ///
 /// This is similar to a Future, except there is no concept of it completing.  It manages its
@@ -394,16 +376,15 @@ impl<T: SimpleAction + Send> Work<T> {
     /// inter-thread sharing mechanisms are needed.
     ///
     /// TODO: Can we come up with a way to allow sharing on the same worker using Rc instead of Arc?
-    pub fn new(action: T) -> Pin<Arc<Self>> {
-        let this = Arc::pin(Self {
-            // SAFETY: will be initialized below, after this is pinned.
-            work: unsafe { mem::zeroed() },
-            action,
-        });
+    pub fn new<P>(action: T) -> P
+    where
+        P: SubmittablePointer<T>,
+    {
+        let this: P = unsafe { SubmittablePointer::new_ptr(action) };
 
-        // SAFETY: Initializes above zero-initialized struct.
+        // SAFETY: Initializes the above zero-initialized struct.
         unsafe {
-            k_work_init(this.work.get(), Some(Self::handler));
+            k_work_init(this.get_work(), Some(P::handler));
         }
 
         this
@@ -413,89 +394,117 @@ impl<T: SimpleAction + Send> Work<T> {
     ///
     /// This can return several possible `Ok` results.  See the docs on [`SubmitResult`] for an
     /// explanation of them.
-    pub fn submit(this: Pin<Arc<Self>>) -> crate::Result<SubmitResult> {
+    pub fn submit<P>(this: P) -> crate::Result<SubmitResult>
+    where
+        P: SubmittablePointer<T>,
+    {
         // We "leak" the arc, so that when the handler runs, it can be safely turned back into an
         // Arc, and the drop on the arc will then run.
-        let work = this.work.get();
+        let work = this.get_work();
 
         // SAFETY: C the code does not perform moves on the data, and the `from_raw` below puts it
         // back into a Pin when it reconstructs the Arc.
-        let this = unsafe { Pin::into_inner_unchecked(this) };
-        let _ = Arc::into_raw(this.clone());
+        unsafe {
+            P::into_raw(this);
+        }
 
         // SAFETY: The Pin ensures this will not move.  Our implementation of drop ensures that the
         // work item is no longer queued when the data is dropped.
         let result = SubmitResult::to_result(unsafe { k_work_submit(work) });
 
-        Self::check_drop(work, &result);
+        P::check_drop(work, &result);
 
         result
     }
 
     /// Submit this work to a specified work queue.
     ///
     /// TODO: Change when we have better wrappers for work queues.
-    pub fn submit_to_queue(
-        this: Pin<Arc<Self>>,
-        queue: &'static WorkQueue,
-    ) -> crate::Result<SubmitResult> {
-        let work = this.work.get();
+    pub fn submit_to_queue<P>(this: P, queue: &'static WorkQueue) -> crate::Result<SubmitResult>
+    where
+        P: SubmittablePointer<T>,
+    {
+        let work = this.get_work();
 
         // "leak" the arc to give to C.  We'll reconstruct it in the handler.
         // SAFETY: The C code does not perform moves on the data, and the `from_raw` below puts it
         // back into a Pin when it reconstructs the Arc.
-        let this = unsafe { Pin::into_inner_unchecked(this) };
-        let _ = Arc::into_raw(this);
+        unsafe {
+            P::into_raw(this);
+        }
 
         // SAFETY: The Pin ensures this will not move.  Our implementation of drop ensures that the
         // work item is no longer queued when the data is dropped.
         let result =
             SubmitResult::to_result(unsafe { k_work_submit_to_queue(queue.item.get(), work) });
 
-        Self::check_drop(work, &result);
+        P::check_drop(work, &result);
 
         result
     }
 
-    /// Callback, through C, but bound by a specific type.
-    extern "C" fn handler(work: *mut k_work) {
-        // We want to avoid needing a `repr(C)` on our struct, so the `k_work` pointer is not
-        // necessarily at the beginning of the struct.
-        // SAFETY: Converts raw pointer to work back into the box.
-        let this = unsafe { Self::from_raw(work) };
+    /// Access the inner action.
+    pub fn action(&self) -> &T {
+        &self.action
+    }
+}
 
-        // Access the action within, still pinned.
-        // SAFETY: It is safe to keep the pin on the interior.
-        let action = unsafe { this.as_ref().map_unchecked(|p| &p.action) };
+/// Capture the kinds of pointers that are safe to submit to work queues.
+pub trait SubmittablePointer<T> {
+    /// Create a new version of a pointer for this particular type.  The pointer should be pinned
+    /// after this call, and can then be initialized and used by C code.
+    unsafe fn new_ptr(action: T) -> Self;
 
-        action.act();
+    /// Given a raw pointer to the work_q burried within, recover the Self pointer containing our
+    /// data.
+    unsafe fn from_raw(ptr: *const k_work) -> Self;
+
+    /// Given our Self, indicate that this reference is now owned by the C code.  For something like
+    /// Arc, this should leak a reference, and is the opposite of from_raw.
+    unsafe fn into_raw(self);
+
+    /// Determine from the submitted work if this work has been enqueued, and if not, cause a "drop"
+    /// to happen on the Self pointer type.
+    fn check_drop(work: *const k_work, result: &crate::Result<SubmitResult>);
+
+    /// Get the inner work pointer.
+    fn get_work(&self) -> *mut k_work;
+
+    /// The low-level handler for this specific type.
+    extern "C" fn handler(work: *mut k_work);
+}
+
+impl<T: SimpleAction + Send> SubmittablePointer<T> for Pin<Arc<Work<T>>> {
+    unsafe fn new_ptr(action: T) -> Self {
+        Arc::pin(Work {
+            work: unsafe { mem::zeroed() },
+            action,
+        })
     }
 
-    /*
-    /// Consume this Arc, returning the internal pointer.  Needs to have a complementary `from_raw`
-    /// called to avoid leaking the item.
-    fn into_raw(this: Pin<Arc<Self>>) -> *const Self {
-        // SAFETY: This removes the Pin guarantee, but is given as a raw pointer to C, which doesn't
-        // generally use move.
-        let this = unsafe { Pin::into_inner_unchecked(this) };
-        Arc::into_raw(this)
+    fn get_work(&self) -> *mut k_work {
+        self.work.get()
     }
-    */
 
-    /// Given a pointer to the work_q burried within, recover the Pinned Box containing our data.
-    unsafe fn from_raw(ptr: *const k_work) -> Pin<Arc<Self>> {
+    unsafe fn from_raw(ptr: *const k_work) -> Self {
         // SAFETY: This fixes the pointer back to the beginning of Self.  This also assumes the
         // pointer is valid.
         let ptr = ptr
             .cast::<u8>()
-            .sub(mem::offset_of!(Self, work))
-            .cast::<Self>();
+            .sub(mem::offset_of!(Work<T>, work))
+            .cast::<Work<T>>();
         let this = Arc::from_raw(ptr);
         Pin::new_unchecked(this)
     }
 
-    /// Determine if this work was submitted, and cause a drop of the Arc to happen if it was not.
-    pub fn check_drop(work: *const k_work, result: &crate::Result<SubmitResult>) {
+    unsafe fn into_raw(self) {
+        // SAFETY: The C code does not perform moves on the data, and the `from_raw` that gets back
+        // our Arc puts it back into the pin when it reconstructs the Arc.
+        let this = unsafe { Pin::into_inner_unchecked(self) };
+        let _ = Arc::into_raw(this.clone());
+    }
+
+    fn check_drop(work: *const k_work, result: &crate::Result<SubmitResult>) {
         if matches!(result, Ok(SubmitResult::AlreadySubmitted) | Err(_)) {
             // SAFETY: If the above submit indicates that it was already running, the work will not
             // be submitted (no additional handle will be called).  "un leak" the work so that it
@@ -507,9 +516,17 @@ impl<T: SimpleAction + Send> Work<T> {
         }
     }
 
-    /// Access the inner action.
-    pub fn action(&self) -> &T {
-        &self.action
+    extern "C" fn handler(work: *mut k_work) {
+        // We want to avoid needing a `repr(C)` on our struct, so the `k_work` pointer is not
+        // necessarily at the beginning of the struct.
+        // SAFETY: Converts raw pointer to work back into the box.
+        let this = unsafe { Self::from_raw(work) };
+
+        // Access the action within, still pinned.
+        // SAFETY: It is safe to keep the pin on the interior.
+        let action = unsafe { this.as_ref().map_unchecked(|p| &p.action) };
+
+        action.act();
     }
 }