654 lines
19 KiB
Rust
654 lines
19 KiB
Rust
//! A queue for sending values between asynchronous tasks.
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//!
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//! Similar to a [`Channel`](crate::channel::Channel), however [`PriorityChannel`] sifts higher priority items to the front of the queue.
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//! Priority is determined by the `Ord` trait. Priority behavior is determined by the [`Kind`](heapless::binary_heap::Kind) parameter of the channel.
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use core::cell::RefCell;
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use core::future::Future;
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use core::pin::Pin;
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use core::task::{Context, Poll};
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use heapless::binary_heap::Kind;
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use heapless::BinaryHeap;
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use crate::blocking_mutex::raw::RawMutex;
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use crate::blocking_mutex::Mutex;
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use crate::channel::{DynamicChannel, DynamicReceiver, DynamicSender, TryReceiveError, TrySendError};
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use crate::waitqueue::WakerRegistration;
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/// Send-only access to a [`PriorityChannel`].
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pub struct Sender<'ch, M, T, K, const N: usize>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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channel: &'ch PriorityChannel<M, T, K, N>,
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}
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impl<'ch, M, T, K, const N: usize> Clone for Sender<'ch, M, T, K, N>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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fn clone(&self) -> Self {
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Sender { channel: self.channel }
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}
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}
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impl<'ch, M, T, K, const N: usize> Copy for Sender<'ch, M, T, K, N>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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}
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impl<'ch, M, T, K, const N: usize> Sender<'ch, M, T, K, N>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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/// Sends a value.
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///
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/// See [`PriorityChannel::send()`]
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pub fn send(&self, message: T) -> SendFuture<'ch, M, T, K, N> {
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self.channel.send(message)
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}
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/// Attempt to immediately send a message.
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///
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/// See [`PriorityChannel::send()`]
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pub fn try_send(&self, message: T) -> Result<(), TrySendError<T>> {
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self.channel.try_send(message)
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}
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/// Allows a poll_fn to poll until the channel is ready to send
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///
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/// See [`PriorityChannel::poll_ready_to_send()`]
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pub fn poll_ready_to_send(&self, cx: &mut Context<'_>) -> Poll<()> {
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self.channel.poll_ready_to_send(cx)
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}
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}
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impl<'ch, M, T, K, const N: usize> From<Sender<'ch, M, T, K, N>> for DynamicSender<'ch, T>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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fn from(s: Sender<'ch, M, T, K, N>) -> Self {
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Self { channel: s.channel }
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}
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}
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/// Receive-only access to a [`PriorityChannel`].
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pub struct Receiver<'ch, M, T, K, const N: usize>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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channel: &'ch PriorityChannel<M, T, K, N>,
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}
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impl<'ch, M, T, K, const N: usize> Clone for Receiver<'ch, M, T, K, N>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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fn clone(&self) -> Self {
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Receiver { channel: self.channel }
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}
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}
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impl<'ch, M, T, K, const N: usize> Copy for Receiver<'ch, M, T, K, N>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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}
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impl<'ch, M, T, K, const N: usize> Receiver<'ch, M, T, K, N>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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/// Receive the next value.
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///
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/// See [`PriorityChannel::receive()`].
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pub fn receive(&self) -> ReceiveFuture<'_, M, T, K, N> {
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self.channel.receive()
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}
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/// Attempt to immediately receive the next value.
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///
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/// See [`PriorityChannel::try_receive()`]
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pub fn try_receive(&self) -> Result<T, TryReceiveError> {
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self.channel.try_receive()
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}
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/// Allows a poll_fn to poll until the channel is ready to receive
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///
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/// See [`PriorityChannel::poll_ready_to_receive()`]
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pub fn poll_ready_to_receive(&self, cx: &mut Context<'_>) -> Poll<()> {
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self.channel.poll_ready_to_receive(cx)
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}
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/// Poll the channel for the next item
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///
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/// See [`PriorityChannel::poll_receive()`]
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pub fn poll_receive(&self, cx: &mut Context<'_>) -> Poll<T> {
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self.channel.poll_receive(cx)
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}
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}
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impl<'ch, M, T, K, const N: usize> From<Receiver<'ch, M, T, K, N>> for DynamicReceiver<'ch, T>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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fn from(s: Receiver<'ch, M, T, K, N>) -> Self {
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Self { channel: s.channel }
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}
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}
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/// Future returned by [`PriorityChannel::receive`] and [`Receiver::receive`].
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#[must_use = "futures do nothing unless you `.await` or poll them"]
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pub struct ReceiveFuture<'ch, M, T, K, const N: usize>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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channel: &'ch PriorityChannel<M, T, K, N>,
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}
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impl<'ch, M, T, K, const N: usize> Future for ReceiveFuture<'ch, M, T, K, N>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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type Output = T;
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fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
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self.channel.poll_receive(cx)
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}
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}
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/// Future returned by [`DynamicReceiver::receive`].
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#[must_use = "futures do nothing unless you `.await` or poll them"]
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pub struct DynamicReceiveFuture<'ch, T> {
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channel: &'ch dyn DynamicChannel<T>,
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}
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impl<'ch, T> Future for DynamicReceiveFuture<'ch, T> {
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type Output = T;
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fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
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match self.channel.try_receive_with_context(Some(cx)) {
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Ok(v) => Poll::Ready(v),
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Err(TryReceiveError::Empty) => Poll::Pending,
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}
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}
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}
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/// Future returned by [`PriorityChannel::send`] and [`Sender::send`].
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#[must_use = "futures do nothing unless you `.await` or poll them"]
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pub struct SendFuture<'ch, M, T, K, const N: usize>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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channel: &'ch PriorityChannel<M, T, K, N>,
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message: Option<T>,
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}
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impl<'ch, M, T, K, const N: usize> Future for SendFuture<'ch, M, T, K, N>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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type Output = ();
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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match self.message.take() {
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Some(m) => match self.channel.try_send_with_context(m, Some(cx)) {
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Ok(..) => Poll::Ready(()),
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Err(TrySendError::Full(m)) => {
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self.message = Some(m);
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Poll::Pending
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}
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},
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None => panic!("Message cannot be None"),
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}
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}
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}
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impl<'ch, M, T, K, const N: usize> Unpin for SendFuture<'ch, M, T, K, N>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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}
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/// Future returned by [`DynamicSender::send`].
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#[must_use = "futures do nothing unless you `.await` or poll them"]
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pub struct DynamicSendFuture<'ch, T> {
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channel: &'ch dyn DynamicChannel<T>,
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message: Option<T>,
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}
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impl<'ch, T> Future for DynamicSendFuture<'ch, T> {
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type Output = ();
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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match self.message.take() {
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Some(m) => match self.channel.try_send_with_context(m, Some(cx)) {
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Ok(..) => Poll::Ready(()),
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Err(TrySendError::Full(m)) => {
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self.message = Some(m);
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Poll::Pending
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}
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},
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None => panic!("Message cannot be None"),
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}
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}
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}
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impl<'ch, T> Unpin for DynamicSendFuture<'ch, T> {}
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struct ChannelState<T, K, const N: usize> {
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queue: BinaryHeap<T, K, N>,
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receiver_waker: WakerRegistration,
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senders_waker: WakerRegistration,
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}
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impl<T, K, const N: usize> ChannelState<T, K, N>
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where
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T: Ord,
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K: Kind,
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{
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const fn new() -> Self {
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ChannelState {
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queue: BinaryHeap::new(),
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receiver_waker: WakerRegistration::new(),
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senders_waker: WakerRegistration::new(),
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}
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}
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fn try_receive(&mut self) -> Result<T, TryReceiveError> {
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self.try_receive_with_context(None)
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}
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fn try_receive_with_context(&mut self, cx: Option<&mut Context<'_>>) -> Result<T, TryReceiveError> {
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if self.queue.len() == self.queue.capacity() {
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self.senders_waker.wake();
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}
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if let Some(message) = self.queue.pop() {
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Ok(message)
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} else {
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if let Some(cx) = cx {
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self.receiver_waker.register(cx.waker());
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}
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Err(TryReceiveError::Empty)
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}
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}
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fn poll_receive(&mut self, cx: &mut Context<'_>) -> Poll<T> {
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if self.queue.len() == self.queue.capacity() {
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self.senders_waker.wake();
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}
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if let Some(message) = self.queue.pop() {
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Poll::Ready(message)
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} else {
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self.receiver_waker.register(cx.waker());
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Poll::Pending
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}
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}
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fn poll_ready_to_receive(&mut self, cx: &mut Context<'_>) -> Poll<()> {
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self.receiver_waker.register(cx.waker());
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if !self.queue.is_empty() {
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Poll::Ready(())
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} else {
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Poll::Pending
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}
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}
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fn try_send(&mut self, message: T) -> Result<(), TrySendError<T>> {
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self.try_send_with_context(message, None)
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}
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fn try_send_with_context(&mut self, message: T, cx: Option<&mut Context<'_>>) -> Result<(), TrySendError<T>> {
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match self.queue.push(message) {
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Ok(()) => {
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self.receiver_waker.wake();
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Ok(())
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}
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Err(message) => {
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if let Some(cx) = cx {
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self.senders_waker.register(cx.waker());
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}
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Err(TrySendError::Full(message))
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}
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}
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}
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fn poll_ready_to_send(&mut self, cx: &mut Context<'_>) -> Poll<()> {
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self.senders_waker.register(cx.waker());
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if !self.queue.len() == self.queue.capacity() {
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Poll::Ready(())
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} else {
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Poll::Pending
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}
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}
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}
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/// A bounded channel for communicating between asynchronous tasks
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/// with backpressure.
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///
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/// The channel will buffer up to the provided number of messages. Once the
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/// buffer is full, attempts to `send` new messages will wait until a message is
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/// received from the channel.
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///
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/// All data sent will become available in the same order as it was sent.
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pub struct PriorityChannel<M, T, K, const N: usize>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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inner: Mutex<M, RefCell<ChannelState<T, K, N>>>,
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}
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impl<M, T, K, const N: usize> PriorityChannel<M, T, K, N>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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/// Establish a new bounded channel. For example, to create one with a NoopMutex:
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///
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/// ```
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/// # use heapless::binary_heap::Max;
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/// use embassy_sync::priority_channel::PriorityChannel;
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/// use embassy_sync::blocking_mutex::raw::NoopRawMutex;
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///
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/// // Declare a bounded channel of 3 u32s.
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/// let mut channel = PriorityChannel::<NoopRawMutex, u32, Max, 3>::new();
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/// ```
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pub const fn new() -> Self {
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Self {
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inner: Mutex::new(RefCell::new(ChannelState::new())),
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}
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}
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fn lock<R>(&self, f: impl FnOnce(&mut ChannelState<T, K, N>) -> R) -> R {
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self.inner.lock(|rc| f(&mut *unwrap!(rc.try_borrow_mut())))
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}
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fn try_receive_with_context(&self, cx: Option<&mut Context<'_>>) -> Result<T, TryReceiveError> {
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self.lock(|c| c.try_receive_with_context(cx))
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}
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/// Poll the channel for the next message
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pub fn poll_receive(&self, cx: &mut Context<'_>) -> Poll<T> {
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self.lock(|c| c.poll_receive(cx))
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}
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fn try_send_with_context(&self, m: T, cx: Option<&mut Context<'_>>) -> Result<(), TrySendError<T>> {
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self.lock(|c| c.try_send_with_context(m, cx))
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}
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/// Allows a poll_fn to poll until the channel is ready to receive
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pub fn poll_ready_to_receive(&self, cx: &mut Context<'_>) -> Poll<()> {
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self.lock(|c| c.poll_ready_to_receive(cx))
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}
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/// Allows a poll_fn to poll until the channel is ready to send
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pub fn poll_ready_to_send(&self, cx: &mut Context<'_>) -> Poll<()> {
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self.lock(|c| c.poll_ready_to_send(cx))
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}
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/// Get a sender for this channel.
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pub fn sender(&self) -> Sender<'_, M, T, K, N> {
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Sender { channel: self }
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}
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/// Get a receiver for this channel.
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pub fn receiver(&self) -> Receiver<'_, M, T, K, N> {
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Receiver { channel: self }
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}
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/// Send a value, waiting until there is capacity.
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///
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/// Sending completes when the value has been pushed to the channel's queue.
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/// This doesn't mean the value has been received yet.
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pub fn send(&self, message: T) -> SendFuture<'_, M, T, K, N> {
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SendFuture {
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channel: self,
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message: Some(message),
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}
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}
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/// Attempt to immediately send a message.
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///
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/// This method differs from [`send`](PriorityChannel::send) by returning immediately if the channel's
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/// buffer is full, instead of waiting.
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///
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/// # Errors
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///
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/// If the channel capacity has been reached, i.e., the channel has `n`
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/// buffered values where `n` is the argument passed to [`PriorityChannel`], then an
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/// error is returned.
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pub fn try_send(&self, message: T) -> Result<(), TrySendError<T>> {
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self.lock(|c| c.try_send(message))
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}
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/// Receive the next value.
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///
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/// If there are no messages in the channel's buffer, this method will
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/// wait until a message is sent.
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pub fn receive(&self) -> ReceiveFuture<'_, M, T, K, N> {
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ReceiveFuture { channel: self }
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}
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/// Attempt to immediately receive a message.
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///
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/// This method will either receive a message from the channel immediately or return an error
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/// if the channel is empty.
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pub fn try_receive(&self) -> Result<T, TryReceiveError> {
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self.lock(|c| c.try_receive())
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}
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}
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/// Implements the DynamicChannel to allow creating types that are unaware of the queue size with the
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/// tradeoff cost of dynamic dispatch.
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impl<M, T, K, const N: usize> DynamicChannel<T> for PriorityChannel<M, T, K, N>
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where
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T: Ord,
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K: Kind,
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M: RawMutex,
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{
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fn try_send_with_context(&self, m: T, cx: Option<&mut Context<'_>>) -> Result<(), TrySendError<T>> {
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PriorityChannel::try_send_with_context(self, m, cx)
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}
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fn try_receive_with_context(&self, cx: Option<&mut Context<'_>>) -> Result<T, TryReceiveError> {
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PriorityChannel::try_receive_with_context(self, cx)
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}
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fn poll_ready_to_send(&self, cx: &mut Context<'_>) -> Poll<()> {
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PriorityChannel::poll_ready_to_send(self, cx)
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}
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fn poll_ready_to_receive(&self, cx: &mut Context<'_>) -> Poll<()> {
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PriorityChannel::poll_ready_to_receive(self, cx)
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}
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fn poll_receive(&self, cx: &mut Context<'_>) -> Poll<T> {
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PriorityChannel::poll_receive(self, cx)
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}
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}
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#[cfg(test)]
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mod tests {
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use core::time::Duration;
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use futures_executor::ThreadPool;
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use futures_timer::Delay;
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use futures_util::task::SpawnExt;
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use heapless::binary_heap::{Kind, Max};
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use static_cell::StaticCell;
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use super::*;
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use crate::blocking_mutex::raw::{CriticalSectionRawMutex, NoopRawMutex};
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fn capacity<T, K, const N: usize>(c: &ChannelState<T, K, N>) -> usize
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where
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T: Ord,
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K: Kind,
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{
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c.queue.capacity() - c.queue.len()
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}
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#[test]
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fn sending_once() {
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let mut c = ChannelState::<u32, Max, 3>::new();
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assert!(c.try_send(1).is_ok());
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assert_eq!(capacity(&c), 2);
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}
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#[test]
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fn sending_when_full() {
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let mut c = ChannelState::<u32, Max, 3>::new();
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let _ = c.try_send(1);
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let _ = c.try_send(1);
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let _ = c.try_send(1);
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match c.try_send(2) {
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Err(TrySendError::Full(2)) => assert!(true),
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_ => assert!(false),
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}
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assert_eq!(capacity(&c), 0);
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}
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#[test]
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fn send_priority() {
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// Prio channel with kind `Max` sifts larger numbers to the front of the queue
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let mut c = ChannelState::<u32, Max, 3>::new();
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assert!(c.try_send(1).is_ok());
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assert!(c.try_send(3).is_ok());
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assert_eq!(c.try_receive().unwrap(), 3);
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assert_eq!(c.try_receive().unwrap(), 1);
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}
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#[test]
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fn receiving_once_with_one_send() {
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let mut c = ChannelState::<u32, Max, 3>::new();
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assert!(c.try_send(1).is_ok());
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assert_eq!(c.try_receive().unwrap(), 1);
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assert_eq!(capacity(&c), 3);
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}
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#[test]
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fn receiving_when_empty() {
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let mut c = ChannelState::<u32, Max, 3>::new();
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match c.try_receive() {
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Err(TryReceiveError::Empty) => assert!(true),
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_ => assert!(false),
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}
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assert_eq!(capacity(&c), 3);
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}
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#[test]
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fn simple_send_and_receive() {
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let c = PriorityChannel::<NoopRawMutex, u32, Max, 3>::new();
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assert!(c.try_send(1).is_ok());
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assert_eq!(c.try_receive().unwrap(), 1);
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}
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#[test]
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fn cloning() {
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let c = PriorityChannel::<NoopRawMutex, u32, Max, 3>::new();
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let r1 = c.receiver();
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let s1 = c.sender();
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let _ = r1.clone();
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let _ = s1.clone();
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}
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#[test]
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fn dynamic_dispatch() {
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let c = PriorityChannel::<NoopRawMutex, u32, Max, 3>::new();
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let s: DynamicSender<'_, u32> = c.sender().into();
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let r: DynamicReceiver<'_, u32> = c.receiver().into();
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assert!(s.try_send(1).is_ok());
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assert_eq!(r.try_receive().unwrap(), 1);
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}
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#[futures_test::test]
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async fn receiver_receives_given_try_send_async() {
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let executor = ThreadPool::new().unwrap();
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static CHANNEL: StaticCell<PriorityChannel<CriticalSectionRawMutex, u32, Max, 3>> = StaticCell::new();
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let c = &*CHANNEL.init(PriorityChannel::new());
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let c2 = c;
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assert!(executor
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.spawn(async move {
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assert!(c2.try_send(1).is_ok());
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})
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.is_ok());
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assert_eq!(c.receive().await, 1);
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}
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#[futures_test::test]
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async fn sender_send_completes_if_capacity() {
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let c = PriorityChannel::<CriticalSectionRawMutex, u32, Max, 1>::new();
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c.send(1).await;
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assert_eq!(c.receive().await, 1);
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}
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#[futures_test::test]
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async fn senders_sends_wait_until_capacity() {
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let executor = ThreadPool::new().unwrap();
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static CHANNEL: StaticCell<PriorityChannel<CriticalSectionRawMutex, u32, Max, 1>> = StaticCell::new();
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let c = &*CHANNEL.init(PriorityChannel::new());
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assert!(c.try_send(1).is_ok());
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let c2 = c;
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let send_task_1 = executor.spawn_with_handle(async move { c2.send(2).await });
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let c2 = c;
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let send_task_2 = executor.spawn_with_handle(async move { c2.send(3).await });
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// Wish I could think of a means of determining that the async send is waiting instead.
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// However, I've used the debugger to observe that the send does indeed wait.
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Delay::new(Duration::from_millis(500)).await;
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assert_eq!(c.receive().await, 1);
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assert!(executor
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.spawn(async move {
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loop {
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c.receive().await;
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}
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})
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.is_ok());
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send_task_1.unwrap().await;
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send_task_2.unwrap().await;
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}
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}
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