Merge #712

712: Add types for channel dynamic dispatch r=lulf a=lulf

* Add internal DynamicChannel trait implemented by Channel that allows
  polling for internal state in a lock safe manner and does not require
  knowing the channel size.
* Existing usage of Sender and Receiver is preserved and does not use
  dynamic dispatch.
* Add DynamicSender and DynamicReceiver types that references the
  channel using the DynamicChannel trait and does not require the const
  generic channel size parameter.

Having the ability not know the channel size is very convenient when you don't want to change all of your channel using code when tuning the size. With this change, existing usage can be kept, and those willing to pay the price for dynamic dispatch may do so.

Co-authored-by: Ulf Lilleengen <lulf@redhat.com>

embassy/src/channel/channel.rs

@@ -66,6 +66,48 @@ where
     }
 }
 
+/// Send-only access to a [`Channel`] without knowing channel size.
+#[derive(Copy)]
+pub struct DynamicSender<'ch, T> {
+    channel: &'ch dyn DynamicChannel<T>,
+}
+
+impl<'ch, T> Clone for DynamicSender<'ch, T> {
+    fn clone(&self) -> Self {
+        DynamicSender {
+            channel: self.channel,
+        }
+    }
+}
+
+impl<'ch, M, T, const N: usize> From<Sender<'ch, M, T, N>> for DynamicSender<'ch, T>
+where
+    M: RawMutex,
+{
+    fn from(s: Sender<'ch, M, T, N>) -> Self {
+        Self { channel: s.channel }
+    }
+}
+
+impl<'ch, T> DynamicSender<'ch, T> {
+    /// Sends a value.
+    ///
+    /// See [`Channel::send()`]
+    pub fn send(&self, message: T) -> DynamicSendFuture<'ch, T> {
+        DynamicSendFuture {
+            channel: self.channel,
+            message: Some(message),
+        }
+    }
+
+    /// Attempt to immediately send a message.
+    ///
+    /// See [`Channel::send()`]
+    pub fn try_send(&self, message: T) -> Result<(), TrySendError<T>> {
+        self.channel.try_send_with_context(message, None)
+    }
+}
+
 /// Receive-only access to a [`Channel`].
 #[derive(Copy)]
 pub struct Receiver<'ch, M, T, const N: usize>
@@ -105,6 +147,47 @@ where
     }
 }
 
+/// Receive-only access to a [`Channel`] without knowing channel size.
+#[derive(Copy)]
+pub struct DynamicReceiver<'ch, T> {
+    channel: &'ch dyn DynamicChannel<T>,
+}
+
+impl<'ch, T> Clone for DynamicReceiver<'ch, T> {
+    fn clone(&self) -> Self {
+        DynamicReceiver {
+            channel: self.channel,
+        }
+    }
+}
+
+impl<'ch, T> DynamicReceiver<'ch, T> {
+    /// Receive the next value.
+    ///
+    /// See [`Channel::recv()`].
+    pub fn recv(&self) -> DynamicRecvFuture<'_, T> {
+        DynamicRecvFuture {
+            channel: self.channel,
+        }
+    }
+
+    /// Attempt to immediately receive the next value.
+    ///
+    /// See [`Channel::try_recv()`]
+    pub fn try_recv(&self) -> Result<T, TryRecvError> {
+        self.channel.try_recv_with_context(None)
+    }
+}
+
+impl<'ch, M, T, const N: usize> From<Receiver<'ch, M, T, N>> for DynamicReceiver<'ch, T>
+where
+    M: RawMutex,
+{
+    fn from(s: Receiver<'ch, M, T, N>) -> Self {
+        Self { channel: s.channel }
+    }
+}
+
 pub struct RecvFuture<'ch, M, T, const N: usize>
 where
     M: RawMutex,
@@ -119,11 +202,25 @@ where
     type Output = T;
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
-        self.channel
-            .lock(|c| match c.try_recv_with_context(Some(cx)) {
+        match self.channel.try_recv_with_context(Some(cx)) {
             Ok(v) => Poll::Ready(v),
             Err(TryRecvError::Empty) => Poll::Pending,
-            })
+        }
+    }
+}
+
+pub struct DynamicRecvFuture<'ch, T> {
+    channel: &'ch dyn DynamicChannel<T>,
+}
+
+impl<'ch, T> Future for DynamicRecvFuture<'ch, T> {
+    type Output = T;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
+        match self.channel.try_recv_with_context(Some(cx)) {
+            Ok(v) => Poll::Ready(v),
+            Err(TryRecvError::Empty) => Poll::Pending,
+        }
     }
 }
 
@@ -143,7 +240,7 @@ where
 
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
         match self.message.take() {
-            Some(m) => match self.channel.lock(|c| c.try_send_with_context(m, Some(cx))) {
+            Some(m) => match self.channel.try_send_with_context(m, Some(cx)) {
                 Ok(..) => Poll::Ready(()),
                 Err(TrySendError::Full(m)) => {
                     self.message = Some(m);
@@ -157,6 +254,40 @@ where
 
 impl<'ch, M, T, const N: usize> Unpin for SendFuture<'ch, M, T, N> where M: RawMutex {}
 
+pub struct DynamicSendFuture<'ch, T> {
+    channel: &'ch dyn DynamicChannel<T>,
+    message: Option<T>,
+}
+
+impl<'ch, T> Future for DynamicSendFuture<'ch, T> {
+    type Output = ();
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.message.take() {
+            Some(m) => match self.channel.try_send_with_context(m, Some(cx)) {
+                Ok(..) => Poll::Ready(()),
+                Err(TrySendError::Full(m)) => {
+                    self.message = Some(m);
+                    Poll::Pending
+                }
+            },
+            None => panic!("Message cannot be None"),
+        }
+    }
+}
+
+impl<'ch, T> Unpin for DynamicSendFuture<'ch, T> {}
+
+trait DynamicChannel<T> {
+    fn try_send_with_context(
+        &self,
+        message: T,
+        cx: Option<&mut Context<'_>>,
+    ) -> Result<(), TrySendError<T>>;
+
+    fn try_recv_with_context(&self, cx: Option<&mut Context<'_>>) -> Result<T, TryRecvError>;
+}
+
 /// Error returned by [`try_recv`](Channel::try_recv).
 #[derive(PartialEq, Eq, Clone, Copy, Debug)]
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
@@ -287,6 +418,18 @@ where
         self.inner.lock(|rc| f(&mut *rc.borrow_mut()))
     }
 
+    fn try_recv_with_context(&self, cx: Option<&mut Context<'_>>) -> Result<T, TryRecvError> {
+        self.lock(|c| c.try_recv_with_context(cx))
+    }
+
+    fn try_send_with_context(
+        &self,
+        m: T,
+        cx: Option<&mut Context<'_>>,
+    ) -> Result<(), TrySendError<T>> {
+        self.lock(|c| c.try_send_with_context(m, cx))
+    }
+
     /// Get a sender for this channel.
     pub fn sender(&self) -> Sender<'_, M, T, N> {
         Sender { channel: self }
@@ -339,6 +482,25 @@ where
     }
 }
 
+/// Implements the DynamicChannel to allow creating types that are unaware of the queue size with the
+/// tradeoff cost of dynamic dispatch.
+impl<M, T, const N: usize> DynamicChannel<T> for Channel<M, T, N>
+where
+    M: RawMutex,
+{
+    fn try_send_with_context(
+        &self,
+        m: T,
+        cx: Option<&mut Context<'_>>,
+    ) -> Result<(), TrySendError<T>> {
+        Channel::try_send_with_context(self, m, cx)
+    }
+
+    fn try_recv_with_context(&self, cx: Option<&mut Context<'_>>) -> Result<T, TryRecvError> {
+        Channel::try_recv_with_context(self, cx)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use core::time::Duration;
@@ -411,6 +573,16 @@ mod tests {
         let _ = s1.clone();
     }
 
+    #[test]
+    fn dynamic_dispatch() {
+        let c = Channel::<NoopRawMutex, u32, 3>::new();
+        let s: DynamicSender<'_, u32> = c.sender().into();
+        let r: DynamicReceiver<'_, u32> = c.receiver().into();
+
+        assert!(s.try_send(1).is_ok());
+        assert_eq!(r.try_recv().unwrap(), 1);
+    }
+
     #[futures_test::test]
     async fn receiver_receives_given_try_send_async() {
         let executor = ThreadPool::new().unwrap();