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1083 lines
32 KiB
Rust
1083 lines
32 KiB
Rust
#![allow(deprecated)]
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use std::cell::UnsafeCell;
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use std::error::Error;
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use std::fmt::{self, Debug, Display};
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use std::future::Future;
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use std::isize;
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use std::marker::PhantomData;
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use std::mem;
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use std::pin::Pin;
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use std::process;
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use std::ptr;
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use std::sync::atomic::{self, AtomicUsize, Ordering};
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use std::sync::Arc;
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use std::task::{Context, Poll};
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use crossbeam_utils::Backoff;
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use crate::stream::Stream;
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use crate::sync::WakerSet;
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/// Creates a bounded multi-producer multi-consumer channel.
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///
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/// This channel has a buffer that can hold at most `cap` messages at a time.
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///
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/// Senders and receivers can be cloned. When all senders associated with a channel get dropped, it
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/// becomes closed. Receive operations on a closed and empty channel return [RecvError] instead of
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/// trying to await a message when using [Receiver::recv] or `None` when used as a [Stream].
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///
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/// # Panics
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///
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/// If `cap` is zero, this function will panic.
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///
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/// # Examples
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///
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/// ```
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/// #![allow(deprecated)]
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/// # fn main() -> Result<(), async_std::sync::RecvError> {
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/// # async_std::task::block_on(async {
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/// #
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/// use std::time::Duration;
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///
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/// use async_std::sync::channel;
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/// use async_std::task;
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///
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/// let (s, r) = channel(1);
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///
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/// // This call returns immediately because there is enough space in the channel.
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/// s.send(1usize).await;
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///
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/// task::spawn(async move {
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/// // This call will have to wait because the channel is full.
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/// // It will be able to complete only after the first message is received.
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/// s.send(2).await;
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/// });
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///
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/// task::sleep(Duration::from_secs(1)).await;
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/// assert_eq!(r.recv().await?, 1);
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/// assert_eq!(r.recv().await?, 2);
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/// # Ok(())
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/// #
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/// # }) }
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/// ```
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#[cfg(feature = "unstable")]
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#[cfg_attr(feature = "docs", doc(cfg(unstable)))]
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#[deprecated = "new channel api at async_std::channel"]
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pub fn channel<T>(cap: usize) -> (Sender<T>, Receiver<T>) {
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let channel = Arc::new(Channel::with_capacity(cap));
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let s = Sender {
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channel: channel.clone(),
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};
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let r = Receiver {
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channel,
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opt_key: None,
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};
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(s, r)
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}
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/// The sending side of a channel.
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///
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/// This struct is created by the [`channel`] function. See its
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/// documentation for more.
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///
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/// [`channel`]: fn.channel.html
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///
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/// # Examples
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///
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/// ```
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/// #![allow(deprecated)]
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/// # async_std::task::block_on(async {
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/// #
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/// use async_std::sync::channel;
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/// use async_std::task;
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///
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/// let (s1, r) = channel(100);
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/// let s2 = s1.clone();
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///
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/// task::spawn(async move { s1.send(1).await });
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/// task::spawn(async move { s2.send(2).await });
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///
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/// let msg1 = r.recv().await.unwrap();
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/// let msg2 = r.recv().await.unwrap();
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///
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/// assert_eq!(msg1 + msg2, 3);
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/// #
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/// # })
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/// ```
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#[cfg(feature = "unstable")]
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#[cfg_attr(feature = "docs", doc(cfg(unstable)))]
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#[deprecated = "new channel api at async_std::channel"]
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pub struct Sender<T> {
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/// The inner channel.
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channel: Arc<Channel<T>>,
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}
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impl<T> Sender<T> {
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/// Sends a message into the channel.
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///
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/// If the channel is full, this method will wait until there is space in the channel.
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///
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/// # Examples
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///
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/// ```
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/// #![allow(deprecated)]
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/// # fn main() -> Result<(), async_std::sync::RecvError> {
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/// # async_std::task::block_on(async {
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/// #
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/// use async_std::sync::channel;
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/// use async_std::task;
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///
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/// let (s, r) = channel(1);
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///
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/// task::spawn(async move {
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/// s.send(1).await;
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/// s.send(2).await;
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/// });
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///
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/// assert_eq!(r.recv().await?, 1);
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/// assert_eq!(r.recv().await?, 2);
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/// assert!(r.recv().await.is_err());
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/// #
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/// # Ok(())
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/// # }) }
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/// ```
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pub async fn send(&self, msg: T) {
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struct SendFuture<'a, T> {
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channel: &'a Channel<T>,
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msg: Option<T>,
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opt_key: Option<usize>,
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}
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impl<T> Unpin for SendFuture<'_, T> {}
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impl<T> Future for SendFuture<'_, 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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loop {
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let msg = self.msg.take().unwrap();
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// If the current task is in the set, remove it.
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if let Some(key) = self.opt_key.take() {
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self.channel.send_wakers.remove(key);
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}
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// Try sending the message.
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match self.channel.try_send(msg) {
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Ok(()) => return Poll::Ready(()),
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Err(TrySendError::Disconnected(msg)) => {
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self.msg = Some(msg);
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return Poll::Pending;
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}
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Err(TrySendError::Full(msg)) => {
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self.msg = Some(msg);
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// Insert this send operation.
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self.opt_key = Some(self.channel.send_wakers.insert(cx));
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// If the channel is still full and not disconnected, return.
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if self.channel.is_full() && !self.channel.is_disconnected() {
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return Poll::Pending;
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}
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}
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}
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}
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}
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}
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impl<T> Drop for SendFuture<'_, T> {
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fn drop(&mut self) {
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// If the current task is still in the set, that means it is being cancelled now.
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// Wake up another task instead.
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if let Some(key) = self.opt_key {
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self.channel.send_wakers.cancel(key);
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}
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}
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}
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SendFuture {
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channel: &self.channel,
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msg: Some(msg),
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opt_key: None,
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}
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.await
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}
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/// Attempts to send a message into the channel.
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///
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/// If the channel is full, this method will return an error.
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///
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/// # Examples
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///
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/// ```
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/// #![allow(deprecated)]
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/// # async_std::task::block_on(async {
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/// #
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/// use async_std::sync::channel;
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///
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/// let (s, r) = channel(1);
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/// assert!(s.try_send(1).is_ok());
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/// assert!(s.try_send(2).is_err());
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/// #
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/// # })
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/// ```
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pub fn try_send(&self, msg: T) -> Result<(), TrySendError<T>> {
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self.channel.try_send(msg)
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}
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/// Returns the channel capacity.
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///
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/// # Examples
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///
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/// ```
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/// #![allow(deprecated)]
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/// use async_std::sync::channel;
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///
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/// let (s, _) = channel::<i32>(5);
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/// assert_eq!(s.capacity(), 5);
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/// ```
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pub fn capacity(&self) -> usize {
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self.channel.cap
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}
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/// Returns `true` if the channel is empty.
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///
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/// # Examples
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///
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/// ```
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/// #![allow(deprecated)]
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/// # async_std::task::block_on(async {
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/// #
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/// use async_std::sync::channel;
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///
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/// let (s, r) = channel(1);
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///
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/// assert!(s.is_empty());
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/// s.send(0).await;
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/// assert!(!s.is_empty());
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/// #
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/// # })
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/// ```
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pub fn is_empty(&self) -> bool {
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self.channel.is_empty()
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}
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/// Returns `true` if the channel is full.
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///
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/// # Examples
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///
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/// ```
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/// #![allow(deprecated)]
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/// # async_std::task::block_on(async {
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/// #
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/// use async_std::sync::channel;
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///
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/// let (s, r) = channel(1);
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///
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/// assert!(!s.is_full());
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/// s.send(0).await;
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/// assert!(s.is_full());
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/// #
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/// # })
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/// ```
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pub fn is_full(&self) -> bool {
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self.channel.is_full()
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}
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/// Returns the number of messages in the channel.
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///
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/// # Examples
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///
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/// ```
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/// #![allow(deprecated)]
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/// # async_std::task::block_on(async {
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/// #
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/// use async_std::sync::channel;
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///
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/// let (s, r) = channel(2);
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/// assert_eq!(s.len(), 0);
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///
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/// s.send(1).await;
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/// s.send(2).await;
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/// assert_eq!(s.len(), 2);
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/// #
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/// # })
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/// ```
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pub fn len(&self) -> usize {
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self.channel.len()
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}
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}
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impl<T> Drop for Sender<T> {
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fn drop(&mut self) {
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// Decrement the sender count and disconnect the channel if it drops down to zero.
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if self.channel.sender_count.fetch_sub(1, Ordering::AcqRel) == 1 {
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self.channel.disconnect();
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}
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}
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}
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impl<T> Clone for Sender<T> {
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fn clone(&self) -> Sender<T> {
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let count = self.channel.sender_count.fetch_add(1, Ordering::Relaxed);
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// Make sure the count never overflows, even if lots of sender clones are leaked.
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if count > isize::MAX as usize {
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process::abort();
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}
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Sender {
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channel: self.channel.clone(),
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}
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}
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}
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impl<T> fmt::Debug for Sender<T> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.pad("Sender { .. }")
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}
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}
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/// The receiving side of a channel.
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///
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/// This type receives messages by calling `recv`. But it also implements the [`Stream`] trait,
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/// which means it can act as an asynchronous iterator. This struct is created by the [`channel`]
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/// function. See its documentation for more.
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///
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/// [`channel`]: fn.channel.html
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/// [`Stream`]: ../stream/trait.Stream.html
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///
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/// # Examples
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///
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/// ```
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/// #![allow(deprecated)]
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/// # fn main() -> Result<(), async_std::sync::RecvError> {
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/// # async_std::task::block_on(async {
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/// #
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/// use std::time::Duration;
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///
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/// use async_std::sync::channel;
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/// use async_std::task;
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///
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/// let (s, r) = channel(100);
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///
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/// task::spawn(async move {
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/// s.send(1usize).await;
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/// task::sleep(Duration::from_secs(1)).await;
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/// s.send(2).await;
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/// });
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///
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/// assert_eq!(r.recv().await?, 1); // Received immediately.
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/// assert_eq!(r.recv().await?, 2); // Received after 1 second.
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/// #
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/// # Ok(())
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/// # }) }
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/// ```
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#[cfg(feature = "unstable")]
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#[cfg_attr(feature = "docs", doc(cfg(unstable)))]
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#[deprecated = "new channel api at async_std::channel"]
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pub struct Receiver<T> {
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/// The inner channel.
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channel: Arc<Channel<T>>,
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|
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/// The key for this receiver in the `channel.stream_wakers` set.
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opt_key: Option<usize>,
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}
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impl<T> Receiver<T> {
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/// Receives a message from the channel.
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///
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/// If the channel is empty and still has senders, this method
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/// will wait until a message is sent into it. Once all senders
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/// have been dropped it will return [RecvError].
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///
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/// # Examples
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///
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/// ```
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/// #![allow(deprecated)]
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/// # fn main() -> Result<(), async_std::sync::RecvError> {
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/// # async_std::task::block_on(async {
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/// #
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/// use async_std::sync::channel;
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/// use async_std::task;
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///
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/// let (s, r) = channel(1);
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///
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/// task::spawn(async move {
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/// s.send(1usize).await;
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/// s.send(2).await;
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/// // Then we drop the sender
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/// });
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///
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/// assert_eq!(r.recv().await?, 1);
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/// assert_eq!(r.recv().await?, 2);
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/// assert!(r.recv().await.is_err());
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/// #
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/// # Ok(())
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/// # }) }
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/// ```
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pub async fn recv(&self) -> Result<T, RecvError> {
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struct RecvFuture<'a, T> {
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channel: &'a Channel<T>,
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opt_key: Option<usize>,
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}
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|
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impl<T> Future for RecvFuture<'_, T> {
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type Output = Result<T, RecvError>;
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|
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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poll_recv(
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&self.channel,
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&self.channel.recv_wakers,
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&mut self.opt_key,
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cx,
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)
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}
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}
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|
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impl<T> Drop for RecvFuture<'_, T> {
|
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fn drop(&mut self) {
|
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// If the current task is still in the set, that means it is being cancelled now.
|
|
if let Some(key) = self.opt_key {
|
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self.channel.recv_wakers.cancel(key);
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}
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}
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}
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|
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RecvFuture {
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channel: &self.channel,
|
|
opt_key: None,
|
|
}
|
|
.await
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}
|
|
|
|
/// Attempts to receive a message from the channel.
|
|
///
|
|
/// If the channel is empty, this method will return an error.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![allow(deprecated)]
|
|
/// # async_std::task::block_on(async {
|
|
/// #
|
|
/// use async_std::sync::channel;
|
|
///
|
|
/// let (s, r) = channel(1);
|
|
///
|
|
/// s.send(1u8).await;
|
|
///
|
|
/// assert!(r.try_recv().is_ok());
|
|
/// assert!(r.try_recv().is_err());
|
|
/// #
|
|
/// # })
|
|
/// ```
|
|
pub fn try_recv(&self) -> Result<T, TryRecvError> {
|
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self.channel.try_recv()
|
|
}
|
|
|
|
/// Returns the channel capacity.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![allow(deprecated)]
|
|
/// use async_std::sync::channel;
|
|
///
|
|
/// let (_, r) = channel::<i32>(5);
|
|
/// assert_eq!(r.capacity(), 5);
|
|
/// ```
|
|
pub fn capacity(&self) -> usize {
|
|
self.channel.cap
|
|
}
|
|
|
|
/// Returns `true` if the channel is empty.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![allow(deprecated)]
|
|
/// # async_std::task::block_on(async {
|
|
/// #
|
|
/// use async_std::sync::channel;
|
|
///
|
|
/// let (s, r) = channel(1);
|
|
///
|
|
/// assert!(r.is_empty());
|
|
/// s.send(0).await;
|
|
/// assert!(!r.is_empty());
|
|
/// #
|
|
/// # })
|
|
/// ```
|
|
pub fn is_empty(&self) -> bool {
|
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self.channel.is_empty()
|
|
}
|
|
|
|
/// Returns `true` if the channel is full.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![allow(deprecated)]
|
|
/// # async_std::task::block_on(async {
|
|
/// #
|
|
/// use async_std::sync::channel;
|
|
///
|
|
/// let (s, r) = channel(1);
|
|
///
|
|
/// assert!(!r.is_full());
|
|
/// s.send(0).await;
|
|
/// assert!(r.is_full());
|
|
/// #
|
|
/// # })
|
|
/// ```
|
|
pub fn is_full(&self) -> bool {
|
|
self.channel.is_full()
|
|
}
|
|
|
|
/// Returns the number of messages in the channel.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![allow(deprecated)]
|
|
/// # async_std::task::block_on(async {
|
|
/// #
|
|
/// use async_std::sync::channel;
|
|
///
|
|
/// let (s, r) = channel(2);
|
|
/// assert_eq!(r.len(), 0);
|
|
///
|
|
/// s.send(1).await;
|
|
/// s.send(2).await;
|
|
/// assert_eq!(r.len(), 2);
|
|
/// #
|
|
/// # })
|
|
/// ```
|
|
pub fn len(&self) -> usize {
|
|
self.channel.len()
|
|
}
|
|
}
|
|
|
|
impl<T> Drop for Receiver<T> {
|
|
fn drop(&mut self) {
|
|
// If the current task is still in the stream set, that means it is being cancelled now.
|
|
if let Some(key) = self.opt_key {
|
|
self.channel.stream_wakers.cancel(key);
|
|
}
|
|
|
|
// Decrement the receiver count and disconnect the channel if it drops down to zero.
|
|
if self.channel.receiver_count.fetch_sub(1, Ordering::AcqRel) == 1 {
|
|
self.channel.disconnect();
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T> Clone for Receiver<T> {
|
|
fn clone(&self) -> Receiver<T> {
|
|
let count = self.channel.receiver_count.fetch_add(1, Ordering::Relaxed);
|
|
|
|
// Make sure the count never overflows, even if lots of receiver clones are leaked.
|
|
if count > isize::MAX as usize {
|
|
process::abort();
|
|
}
|
|
|
|
Receiver {
|
|
channel: self.channel.clone(),
|
|
opt_key: None,
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T> Stream for Receiver<T> {
|
|
type Item = T;
|
|
|
|
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
|
|
let this = &mut *self;
|
|
let res = futures_core::ready!(poll_recv(
|
|
&this.channel,
|
|
&this.channel.stream_wakers,
|
|
&mut this.opt_key,
|
|
cx,
|
|
));
|
|
Poll::Ready(res.ok())
|
|
}
|
|
}
|
|
|
|
impl<T> fmt::Debug for Receiver<T> {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
f.pad("Receiver { .. }")
|
|
}
|
|
}
|
|
|
|
/// Polls a receive operation on a channel.
|
|
///
|
|
/// If the receive operation is blocked, the current task will be inserted into `wakers` and its
|
|
/// associated key will then be stored in `opt_key`.
|
|
fn poll_recv<T>(
|
|
channel: &Channel<T>,
|
|
wakers: &WakerSet,
|
|
opt_key: &mut Option<usize>,
|
|
cx: &mut Context<'_>,
|
|
) -> Poll<Result<T, RecvError>> {
|
|
loop {
|
|
// If the current task is in the set, remove it.
|
|
if let Some(key) = opt_key.take() {
|
|
wakers.remove(key);
|
|
}
|
|
|
|
// Try receiving a message.
|
|
match channel.try_recv() {
|
|
Ok(msg) => return Poll::Ready(Ok(msg)),
|
|
Err(TryRecvError::Disconnected) => return Poll::Ready(Err(RecvError {})),
|
|
Err(TryRecvError::Empty) => {
|
|
// Insert this receive operation.
|
|
*opt_key = Some(wakers.insert(cx));
|
|
|
|
// If the channel is still empty and not disconnected, return.
|
|
if channel.is_empty() && !channel.is_disconnected() {
|
|
return Poll::Pending;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// A slot in a channel.
|
|
struct Slot<T> {
|
|
/// The current stamp.
|
|
stamp: AtomicUsize,
|
|
|
|
/// The message in this slot.
|
|
msg: UnsafeCell<T>,
|
|
}
|
|
|
|
/// Bounded channel based on a preallocated array.
|
|
struct Channel<T> {
|
|
/// The head of the channel.
|
|
///
|
|
/// This value is a "stamp" consisting of an index into the buffer, a mark bit, and a lap, but
|
|
/// packed into a single `usize`. The lower bits represent the index, while the upper bits
|
|
/// represent the lap. The mark bit in the head is always zero.
|
|
///
|
|
/// Messages are popped from the head of the channel.
|
|
head: AtomicUsize,
|
|
|
|
/// The tail of the channel.
|
|
///
|
|
/// This value is a "stamp" consisting of an index into the buffer, a mark bit, and a lap, but
|
|
/// packed into a single `usize`. The lower bits represent the index, while the upper bits
|
|
/// represent the lap. The mark bit indicates that the channel is disconnected.
|
|
///
|
|
/// Messages are pushed into the tail of the channel.
|
|
tail: AtomicUsize,
|
|
|
|
/// The buffer holding slots.
|
|
buffer: *mut Slot<T>,
|
|
|
|
/// The channel capacity.
|
|
cap: usize,
|
|
|
|
/// A stamp with the value of `{ lap: 1, mark: 0, index: 0 }`.
|
|
one_lap: usize,
|
|
|
|
/// If this bit is set in the tail, that means either all senders were dropped or all receivers
|
|
/// were dropped.
|
|
mark_bit: usize,
|
|
|
|
/// Send operations waiting while the channel is full.
|
|
send_wakers: WakerSet,
|
|
|
|
/// Receive operations waiting while the channel is empty and not disconnected.
|
|
recv_wakers: WakerSet,
|
|
|
|
/// Streams waiting while the channel is empty and not disconnected.
|
|
stream_wakers: WakerSet,
|
|
|
|
/// The number of currently active `Sender`s.
|
|
sender_count: AtomicUsize,
|
|
|
|
/// The number of currently active `Receivers`s.
|
|
receiver_count: AtomicUsize,
|
|
|
|
/// Indicates that dropping a `Channel<T>` may drop values of type `T`.
|
|
_marker: PhantomData<T>,
|
|
}
|
|
|
|
unsafe impl<T: Send> Send for Channel<T> {}
|
|
unsafe impl<T: Send> Sync for Channel<T> {}
|
|
impl<T> Unpin for Channel<T> {}
|
|
|
|
impl<T> Channel<T> {
|
|
/// Creates a bounded channel of capacity `cap`.
|
|
fn with_capacity(cap: usize) -> Self {
|
|
assert!(cap > 0, "capacity must be positive");
|
|
|
|
// Compute constants `mark_bit` and `one_lap`.
|
|
let mark_bit = (cap + 1).next_power_of_two();
|
|
let one_lap = mark_bit * 2;
|
|
|
|
// Head is initialized to `{ lap: 0, mark: 0, index: 0 }`.
|
|
let head = 0;
|
|
// Tail is initialized to `{ lap: 0, mark: 0, index: 0 }`.
|
|
let tail = 0;
|
|
|
|
// Allocate a buffer of `cap` slots.
|
|
let buffer = {
|
|
let mut v = Vec::<Slot<T>>::with_capacity(cap);
|
|
let ptr = v.as_mut_ptr();
|
|
mem::forget(v);
|
|
ptr
|
|
};
|
|
|
|
// Initialize stamps in the slots.
|
|
for i in 0..cap {
|
|
unsafe {
|
|
// Set the stamp to `{ lap: 0, mark: 0, index: i }`.
|
|
let slot = buffer.add(i);
|
|
ptr::write(&mut (*slot).stamp, AtomicUsize::new(i));
|
|
}
|
|
}
|
|
|
|
Channel {
|
|
buffer,
|
|
cap,
|
|
one_lap,
|
|
mark_bit,
|
|
head: AtomicUsize::new(head),
|
|
tail: AtomicUsize::new(tail),
|
|
send_wakers: WakerSet::new(),
|
|
recv_wakers: WakerSet::new(),
|
|
stream_wakers: WakerSet::new(),
|
|
sender_count: AtomicUsize::new(1),
|
|
receiver_count: AtomicUsize::new(1),
|
|
_marker: PhantomData,
|
|
}
|
|
}
|
|
|
|
/// Attempts to send a message.
|
|
fn try_send(&self, msg: T) -> Result<(), TrySendError<T>> {
|
|
let backoff = Backoff::new();
|
|
let mut tail = self.tail.load(Ordering::Relaxed);
|
|
|
|
loop {
|
|
// Extract mark bit from the tail and unset it.
|
|
//
|
|
// If the mark bit was set (which means all receivers have been dropped), we will still
|
|
// send the message into the channel if there is enough capacity. The message will get
|
|
// dropped when the channel is dropped (which means when all senders are also dropped).
|
|
let mark_bit = tail & self.mark_bit;
|
|
tail ^= mark_bit;
|
|
|
|
// Deconstruct the tail.
|
|
let index = tail & (self.mark_bit - 1);
|
|
let lap = tail & !(self.one_lap - 1);
|
|
|
|
// Inspect the corresponding slot.
|
|
let slot = unsafe { &*self.buffer.add(index) };
|
|
let stamp = slot.stamp.load(Ordering::Acquire);
|
|
|
|
// If the tail and the stamp match, we may attempt to push.
|
|
if tail == stamp {
|
|
let new_tail = if index + 1 < self.cap {
|
|
// Same lap, incremented index.
|
|
// Set to `{ lap: lap, mark: 0, index: index + 1 }`.
|
|
tail + 1
|
|
} else {
|
|
// One lap forward, index wraps around to zero.
|
|
// Set to `{ lap: lap.wrapping_add(1), mark: 0, index: 0 }`.
|
|
lap.wrapping_add(self.one_lap)
|
|
};
|
|
|
|
// Try moving the tail.
|
|
match self.tail.compare_exchange_weak(
|
|
tail | mark_bit,
|
|
new_tail | mark_bit,
|
|
Ordering::SeqCst,
|
|
Ordering::Relaxed,
|
|
) {
|
|
Ok(_) => {
|
|
// Write the message into the slot and update the stamp.
|
|
unsafe { slot.msg.get().write(msg) };
|
|
let stamp = tail + 1;
|
|
slot.stamp.store(stamp, Ordering::Release);
|
|
|
|
// Wake a blocked receive operation.
|
|
self.recv_wakers.notify_one();
|
|
|
|
// Wake all blocked streams.
|
|
self.stream_wakers.notify_all();
|
|
|
|
return Ok(());
|
|
}
|
|
Err(t) => {
|
|
tail = t;
|
|
backoff.spin();
|
|
}
|
|
}
|
|
} else if stamp.wrapping_add(self.one_lap) == tail + 1 {
|
|
atomic::fence(Ordering::SeqCst);
|
|
let head = self.head.load(Ordering::Relaxed);
|
|
|
|
// If the head lags one lap behind the tail as well...
|
|
if head.wrapping_add(self.one_lap) == tail {
|
|
// ...then the channel is full.
|
|
|
|
// Check if the channel is disconnected.
|
|
if mark_bit != 0 {
|
|
return Err(TrySendError::Disconnected(msg));
|
|
} else {
|
|
return Err(TrySendError::Full(msg));
|
|
}
|
|
}
|
|
|
|
backoff.spin();
|
|
tail = self.tail.load(Ordering::Relaxed);
|
|
} else {
|
|
// Snooze because we need to wait for the stamp to get updated.
|
|
backoff.snooze();
|
|
tail = self.tail.load(Ordering::Relaxed);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Attempts to receive a message.
|
|
fn try_recv(&self) -> Result<T, TryRecvError> {
|
|
let backoff = Backoff::new();
|
|
let mut head = self.head.load(Ordering::Relaxed);
|
|
|
|
loop {
|
|
// Deconstruct the head.
|
|
let index = head & (self.mark_bit - 1);
|
|
let lap = head & !(self.one_lap - 1);
|
|
|
|
// Inspect the corresponding slot.
|
|
let slot = unsafe { &*self.buffer.add(index) };
|
|
let stamp = slot.stamp.load(Ordering::Acquire);
|
|
|
|
// If the the stamp is ahead of the head by 1, we may attempt to pop.
|
|
if head + 1 == stamp {
|
|
let new = if index + 1 < self.cap {
|
|
// Same lap, incremented index.
|
|
// Set to `{ lap: lap, mark: 0, index: index + 1 }`.
|
|
head + 1
|
|
} else {
|
|
// One lap forward, index wraps around to zero.
|
|
// Set to `{ lap: lap.wrapping_add(1), mark: 0, index: 0 }`.
|
|
lap.wrapping_add(self.one_lap)
|
|
};
|
|
|
|
// Try moving the head.
|
|
match self.head.compare_exchange_weak(
|
|
head,
|
|
new,
|
|
Ordering::SeqCst,
|
|
Ordering::Relaxed,
|
|
) {
|
|
Ok(_) => {
|
|
// Read the message from the slot and update the stamp.
|
|
let msg = unsafe { slot.msg.get().read() };
|
|
let stamp = head.wrapping_add(self.one_lap);
|
|
slot.stamp.store(stamp, Ordering::Release);
|
|
|
|
// Wake a blocked send operation.
|
|
self.send_wakers.notify_one();
|
|
|
|
return Ok(msg);
|
|
}
|
|
Err(h) => {
|
|
head = h;
|
|
backoff.spin();
|
|
}
|
|
}
|
|
} else if stamp == head {
|
|
atomic::fence(Ordering::SeqCst);
|
|
let tail = self.tail.load(Ordering::Relaxed);
|
|
|
|
// If the tail equals the head, that means the channel is empty.
|
|
if (tail & !self.mark_bit) == head {
|
|
// If the channel is disconnected...
|
|
if tail & self.mark_bit != 0 {
|
|
return Err(TryRecvError::Disconnected);
|
|
} else {
|
|
// Otherwise, the receive operation is not ready.
|
|
return Err(TryRecvError::Empty);
|
|
}
|
|
}
|
|
|
|
backoff.spin();
|
|
head = self.head.load(Ordering::Relaxed);
|
|
} else {
|
|
// Snooze because we need to wait for the stamp to get updated.
|
|
backoff.snooze();
|
|
head = self.head.load(Ordering::Relaxed);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Returns the current number of messages inside the channel.
|
|
fn len(&self) -> usize {
|
|
loop {
|
|
// Load the tail, then load the head.
|
|
let tail = self.tail.load(Ordering::SeqCst);
|
|
let head = self.head.load(Ordering::SeqCst);
|
|
|
|
// If the tail didn't change, we've got consistent values to work with.
|
|
if self.tail.load(Ordering::SeqCst) == tail {
|
|
let hix = head & (self.mark_bit - 1);
|
|
let tix = tail & (self.mark_bit - 1);
|
|
|
|
return if hix < tix {
|
|
tix - hix
|
|
} else if hix > tix {
|
|
self.cap - hix + tix
|
|
} else if (tail & !self.mark_bit) == head {
|
|
0
|
|
} else {
|
|
self.cap
|
|
};
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Returns `true` if the channel is disconnected.
|
|
pub fn is_disconnected(&self) -> bool {
|
|
self.tail.load(Ordering::SeqCst) & self.mark_bit != 0
|
|
}
|
|
|
|
/// Returns `true` if the channel is empty.
|
|
fn is_empty(&self) -> bool {
|
|
let head = self.head.load(Ordering::SeqCst);
|
|
let tail = self.tail.load(Ordering::SeqCst);
|
|
|
|
// Is the tail equal to the head?
|
|
//
|
|
// Note: If the head changes just before we load the tail, that means there was a moment
|
|
// when the channel was not empty, so it is safe to just return `false`.
|
|
(tail & !self.mark_bit) == head
|
|
}
|
|
|
|
/// Returns `true` if the channel is full.
|
|
fn is_full(&self) -> bool {
|
|
let tail = self.tail.load(Ordering::SeqCst);
|
|
let head = self.head.load(Ordering::SeqCst);
|
|
|
|
// Is the head lagging one lap behind tail?
|
|
//
|
|
// Note: If the tail changes just before we load the head, that means there was a moment
|
|
// when the channel was not full, so it is safe to just return `false`.
|
|
head.wrapping_add(self.one_lap) == tail & !self.mark_bit
|
|
}
|
|
|
|
/// Disconnects the channel and wakes up all blocked operations.
|
|
fn disconnect(&self) {
|
|
let tail = self.tail.fetch_or(self.mark_bit, Ordering::SeqCst);
|
|
|
|
if tail & self.mark_bit == 0 {
|
|
// Notify everyone blocked on this channel.
|
|
self.send_wakers.notify_all();
|
|
self.recv_wakers.notify_all();
|
|
self.stream_wakers.notify_all();
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T> Drop for Channel<T> {
|
|
fn drop(&mut self) {
|
|
// Get the index of the head.
|
|
let hix = self.head.load(Ordering::Relaxed) & (self.mark_bit - 1);
|
|
|
|
// Loop over all slots that hold a message and drop them.
|
|
for i in 0..self.len() {
|
|
// Compute the index of the next slot holding a message.
|
|
let index = if hix + i < self.cap {
|
|
hix + i
|
|
} else {
|
|
hix + i - self.cap
|
|
};
|
|
|
|
unsafe {
|
|
self.buffer.add(index).drop_in_place();
|
|
}
|
|
}
|
|
|
|
// Finally, deallocate the buffer, but don't run any destructors.
|
|
unsafe {
|
|
Vec::from_raw_parts(self.buffer, 0, self.cap);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// An error returned from the `try_send` method.
|
|
#[cfg(feature = "unstable")]
|
|
#[cfg_attr(feature = "docs", doc(cfg(unstable)))]
|
|
#[derive(PartialEq, Eq)]
|
|
#[deprecated = "new channel api at async_std::channel"]
|
|
pub enum TrySendError<T> {
|
|
/// The channel is full but not disconnected.
|
|
Full(T),
|
|
|
|
/// The channel is full and disconnected.
|
|
Disconnected(T),
|
|
}
|
|
|
|
impl<T> Error for TrySendError<T> {}
|
|
|
|
impl<T> Debug for TrySendError<T> {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
match self {
|
|
Self::Full(_) => Debug::fmt("Full<T>", f),
|
|
Self::Disconnected(_) => Debug::fmt("Disconnected<T>", f),
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T> Display for TrySendError<T> {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
match self {
|
|
Self::Full(_) => Display::fmt("The channel is full.", f),
|
|
Self::Disconnected(_) => Display::fmt("The channel is full and disconnected.", f),
|
|
}
|
|
}
|
|
}
|
|
|
|
/// An error returned from the `try_recv` method.
|
|
#[cfg(feature = "unstable")]
|
|
#[cfg_attr(feature = "docs", doc(cfg(unstable)))]
|
|
#[derive(Debug, PartialEq, Eq)]
|
|
#[deprecated = "new channel api at async_std::channel"]
|
|
pub enum TryRecvError {
|
|
/// The channel is empty but not disconnected.
|
|
Empty,
|
|
|
|
/// The channel is empty and disconnected.
|
|
Disconnected,
|
|
}
|
|
|
|
impl Error for TryRecvError {}
|
|
|
|
impl Display for TryRecvError {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
match self {
|
|
Self::Empty => Display::fmt("The channel is empty.", f),
|
|
Self::Disconnected => Display::fmt("The channel is empty and disconnected.", f),
|
|
}
|
|
}
|
|
}
|
|
|
|
/// An error returned from the `recv` method.
|
|
#[cfg(feature = "unstable")]
|
|
#[cfg_attr(feature = "docs", doc(cfg(unstable)))]
|
|
#[derive(Debug, PartialEq, Eq)]
|
|
#[deprecated = "new channel api at async_std::channel"]
|
|
pub struct RecvError;
|
|
|
|
impl Error for RecvError {}
|
|
|
|
impl Display for RecvError {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
Display::fmt("The channel is empty.", f)
|
|
}
|
|
}
|