Initial import of crossbeam-channel-0.5.0.
Bug: 155309706
Change-Id: I8a4696d18bfd2efa9ae51fa0072a40aa45c219a9
diff --git a/src/channel.rs b/src/channel.rs
new file mode 100644
index 0000000..ebcd652
--- /dev/null
+++ b/src/channel.rs
@@ -0,0 +1,1510 @@
+//! The channel interface.
+
+use std::fmt;
+use std::iter::FusedIterator;
+use std::mem;
+use std::panic::{RefUnwindSafe, UnwindSafe};
+use std::sync::Arc;
+use std::time::{Duration, Instant};
+
+use crate::context::Context;
+use crate::counter;
+use crate::err::{
+ RecvError, RecvTimeoutError, SendError, SendTimeoutError, TryRecvError, TrySendError,
+};
+use crate::flavors;
+use crate::select::{Operation, SelectHandle, Token};
+
+/// Creates a channel of unbounded capacity.
+///
+/// This channel has a growable buffer that can hold any number of messages at a time.
+///
+/// # Examples
+///
+/// ```
+/// use std::thread;
+/// use crossbeam_channel::unbounded;
+///
+/// let (s, r) = unbounded();
+///
+/// // Computes the n-th Fibonacci number.
+/// fn fib(n: i32) -> i32 {
+/// if n <= 1 {
+/// n
+/// } else {
+/// fib(n - 1) + fib(n - 2)
+/// }
+/// }
+///
+/// // Spawn an asynchronous computation.
+/// thread::spawn(move || s.send(fib(20)).unwrap());
+///
+/// // Print the result of the computation.
+/// println!("{}", r.recv().unwrap());
+/// ```
+pub fn unbounded<T>() -> (Sender<T>, Receiver<T>) {
+ let (s, r) = counter::new(flavors::list::Channel::new());
+ let s = Sender {
+ flavor: SenderFlavor::List(s),
+ };
+ let r = Receiver {
+ flavor: ReceiverFlavor::List(r),
+ };
+ (s, r)
+}
+
+/// Creates a channel of bounded capacity.
+///
+/// This channel has a buffer that can hold at most `cap` messages at a time.
+///
+/// A special case is zero-capacity channel, which cannot hold any messages. Instead, send and
+/// receive operations must appear at the same time in order to pair up and pass the message over.
+///
+/// # Examples
+///
+/// A channel of capacity 1:
+///
+/// ```
+/// use std::thread;
+/// use std::time::Duration;
+/// use crossbeam_channel::bounded;
+///
+/// let (s, r) = bounded(1);
+///
+/// // This call returns immediately because there is enough space in the channel.
+/// s.send(1).unwrap();
+///
+/// thread::spawn(move || {
+/// // This call blocks the current thread because the channel is full.
+/// // It will be able to complete only after the first message is received.
+/// s.send(2).unwrap();
+/// });
+///
+/// thread::sleep(Duration::from_secs(1));
+/// assert_eq!(r.recv(), Ok(1));
+/// assert_eq!(r.recv(), Ok(2));
+/// ```
+///
+/// A zero-capacity channel:
+///
+/// ```
+/// use std::thread;
+/// use std::time::Duration;
+/// use crossbeam_channel::bounded;
+///
+/// let (s, r) = bounded(0);
+///
+/// thread::spawn(move || {
+/// // This call blocks the current thread until a receive operation appears
+/// // on the other side of the channel.
+/// s.send(1).unwrap();
+/// });
+///
+/// thread::sleep(Duration::from_secs(1));
+/// assert_eq!(r.recv(), Ok(1));
+/// ```
+pub fn bounded<T>(cap: usize) -> (Sender<T>, Receiver<T>) {
+ if cap == 0 {
+ let (s, r) = counter::new(flavors::zero::Channel::new());
+ let s = Sender {
+ flavor: SenderFlavor::Zero(s),
+ };
+ let r = Receiver {
+ flavor: ReceiverFlavor::Zero(r),
+ };
+ (s, r)
+ } else {
+ let (s, r) = counter::new(flavors::array::Channel::with_capacity(cap));
+ let s = Sender {
+ flavor: SenderFlavor::Array(s),
+ };
+ let r = Receiver {
+ flavor: ReceiverFlavor::Array(r),
+ };
+ (s, r)
+ }
+}
+
+/// Creates a receiver that delivers a message after a certain duration of time.
+///
+/// The channel is bounded with capacity of 1 and never gets disconnected. Exactly one message will
+/// be sent into the channel after `duration` elapses. The message is the instant at which it is
+/// sent.
+///
+/// # Examples
+///
+/// Using an `after` channel for timeouts:
+///
+/// ```
+/// use std::time::Duration;
+/// use crossbeam_channel::{after, select, unbounded};
+///
+/// let (s, r) = unbounded::<i32>();
+/// let timeout = Duration::from_millis(100);
+///
+/// select! {
+/// recv(r) -> msg => println!("received {:?}", msg),
+/// recv(after(timeout)) -> _ => println!("timed out"),
+/// }
+/// ```
+///
+/// When the message gets sent:
+///
+/// ```
+/// use std::thread;
+/// use std::time::{Duration, Instant};
+/// use crossbeam_channel::after;
+///
+/// // Converts a number of milliseconds into a `Duration`.
+/// let ms = |ms| Duration::from_millis(ms);
+///
+/// // Returns `true` if `a` and `b` are very close `Instant`s.
+/// let eq = |a, b| a + ms(50) > b && b + ms(50) > a;
+///
+/// let start = Instant::now();
+/// let r = after(ms(100));
+///
+/// thread::sleep(ms(500));
+///
+/// // This message was sent 100 ms from the start and received 500 ms from the start.
+/// assert!(eq(r.recv().unwrap(), start + ms(100)));
+/// assert!(eq(Instant::now(), start + ms(500)));
+/// ```
+pub fn after(duration: Duration) -> Receiver<Instant> {
+ Receiver {
+ flavor: ReceiverFlavor::At(Arc::new(flavors::at::Channel::new_timeout(duration))),
+ }
+}
+
+/// Creates a receiver that delivers a message at a certain instant in time.
+///
+/// The channel is bounded with capacity of 1 and never gets disconnected. Exactly one message will
+/// be sent into the channel at the moment in time `when`. The message is the instant at which it
+/// is sent, which is the same as `when`. If `when` is in the past, the message will be delivered
+/// instantly to the receiver.
+///
+/// # Examples
+///
+/// Using an `at` channel for timeouts:
+///
+/// ```
+/// use std::time::{Instant, Duration};
+/// use crossbeam_channel::{at, select, unbounded};
+///
+/// let (s, r) = unbounded::<i32>();
+/// let deadline = Instant::now() + Duration::from_millis(500);
+///
+/// select! {
+/// recv(r) -> msg => println!("received {:?}", msg),
+/// recv(at(deadline)) -> _ => println!("timed out"),
+/// }
+/// ```
+///
+/// When the message gets sent:
+///
+/// ```
+/// use std::time::{Duration, Instant};
+/// use crossbeam_channel::at;
+///
+/// // Converts a number of milliseconds into a `Duration`.
+/// let ms = |ms| Duration::from_millis(ms);
+///
+/// let start = Instant::now();
+/// let end = start + ms(100);
+///
+/// let r = at(end);
+///
+/// // This message was sent 100 ms from the start
+/// assert_eq!(r.recv().unwrap(), end);
+/// assert!(Instant::now() > start + ms(100));
+/// ```
+pub fn at(when: Instant) -> Receiver<Instant> {
+ Receiver {
+ flavor: ReceiverFlavor::At(Arc::new(flavors::at::Channel::new_deadline(when))),
+ }
+}
+
+/// Creates a receiver that never delivers messages.
+///
+/// The channel is bounded with capacity of 0 and never gets disconnected.
+///
+/// # Examples
+///
+/// Using a `never` channel to optionally add a timeout to [`select!`]:
+///
+/// ```
+/// use std::thread;
+/// use std::time::Duration;
+/// use crossbeam_channel::{after, select, never, unbounded};
+///
+/// let (s, r) = unbounded();
+///
+/// thread::spawn(move || {
+/// thread::sleep(Duration::from_secs(1));
+/// s.send(1).unwrap();
+/// });
+///
+/// // Suppose this duration can be a `Some` or a `None`.
+/// let duration = Some(Duration::from_millis(100));
+///
+/// // Create a channel that times out after the specified duration.
+/// let timeout = duration
+/// .map(|d| after(d))
+/// .unwrap_or(never());
+///
+/// select! {
+/// recv(r) -> msg => assert_eq!(msg, Ok(1)),
+/// recv(timeout) -> _ => println!("timed out"),
+/// }
+/// ```
+///
+/// [`select!`]: macro.select.html
+pub fn never<T>() -> Receiver<T> {
+ Receiver {
+ flavor: ReceiverFlavor::Never(flavors::never::Channel::new()),
+ }
+}
+
+/// Creates a receiver that delivers messages periodically.
+///
+/// The channel is bounded with capacity of 1 and never gets disconnected. Messages will be
+/// sent into the channel in intervals of `duration`. Each message is the instant at which it is
+/// sent.
+///
+/// # Examples
+///
+/// Using a `tick` channel to periodically print elapsed time:
+///
+/// ```
+/// use std::time::{Duration, Instant};
+/// use crossbeam_channel::tick;
+///
+/// let start = Instant::now();
+/// let ticker = tick(Duration::from_millis(100));
+///
+/// for _ in 0..5 {
+/// ticker.recv().unwrap();
+/// println!("elapsed: {:?}", start.elapsed());
+/// }
+/// ```
+///
+/// When messages get sent:
+///
+/// ```
+/// use std::thread;
+/// use std::time::{Duration, Instant};
+/// use crossbeam_channel::tick;
+///
+/// // Converts a number of milliseconds into a `Duration`.
+/// let ms = |ms| Duration::from_millis(ms);
+///
+/// // Returns `true` if `a` and `b` are very close `Instant`s.
+/// let eq = |a, b| a + ms(50) > b && b + ms(50) > a;
+///
+/// let start = Instant::now();
+/// let r = tick(ms(100));
+///
+/// // This message was sent 100 ms from the start and received 100 ms from the start.
+/// assert!(eq(r.recv().unwrap(), start + ms(100)));
+/// assert!(eq(Instant::now(), start + ms(100)));
+///
+/// thread::sleep(ms(500));
+///
+/// // This message was sent 200 ms from the start and received 600 ms from the start.
+/// assert!(eq(r.recv().unwrap(), start + ms(200)));
+/// assert!(eq(Instant::now(), start + ms(600)));
+///
+/// // This message was sent 700 ms from the start and received 700 ms from the start.
+/// assert!(eq(r.recv().unwrap(), start + ms(700)));
+/// assert!(eq(Instant::now(), start + ms(700)));
+/// ```
+pub fn tick(duration: Duration) -> Receiver<Instant> {
+ Receiver {
+ flavor: ReceiverFlavor::Tick(Arc::new(flavors::tick::Channel::new(duration))),
+ }
+}
+
+/// The sending side of a channel.
+///
+/// # Examples
+///
+/// ```
+/// use std::thread;
+/// use crossbeam_channel::unbounded;
+///
+/// let (s1, r) = unbounded();
+/// let s2 = s1.clone();
+///
+/// thread::spawn(move || s1.send(1).unwrap());
+/// thread::spawn(move || s2.send(2).unwrap());
+///
+/// let msg1 = r.recv().unwrap();
+/// let msg2 = r.recv().unwrap();
+///
+/// assert_eq!(msg1 + msg2, 3);
+/// ```
+pub struct Sender<T> {
+ flavor: SenderFlavor<T>,
+}
+
+/// Sender flavors.
+enum SenderFlavor<T> {
+ /// Bounded channel based on a preallocated array.
+ Array(counter::Sender<flavors::array::Channel<T>>),
+
+ /// Unbounded channel implemented as a linked list.
+ List(counter::Sender<flavors::list::Channel<T>>),
+
+ /// Zero-capacity channel.
+ Zero(counter::Sender<flavors::zero::Channel<T>>),
+}
+
+unsafe impl<T: Send> Send for Sender<T> {}
+unsafe impl<T: Send> Sync for Sender<T> {}
+
+impl<T> UnwindSafe for Sender<T> {}
+impl<T> RefUnwindSafe for Sender<T> {}
+
+impl<T> Sender<T> {
+ /// Attempts to send a message into the channel without blocking.
+ ///
+ /// This method will either send a message into the channel immediately or return an error if
+ /// the channel is full or disconnected. The returned error contains the original message.
+ ///
+ /// If called on a zero-capacity channel, this method will send the message only if there
+ /// happens to be a receive operation on the other side of the channel at the same time.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::{bounded, TrySendError};
+ ///
+ /// let (s, r) = bounded(1);
+ ///
+ /// assert_eq!(s.try_send(1), Ok(()));
+ /// assert_eq!(s.try_send(2), Err(TrySendError::Full(2)));
+ ///
+ /// drop(r);
+ /// assert_eq!(s.try_send(3), Err(TrySendError::Disconnected(3)));
+ /// ```
+ pub fn try_send(&self, msg: T) -> Result<(), TrySendError<T>> {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.try_send(msg),
+ SenderFlavor::List(chan) => chan.try_send(msg),
+ SenderFlavor::Zero(chan) => chan.try_send(msg),
+ }
+ }
+
+ /// Blocks the current thread until a message is sent or the channel is disconnected.
+ ///
+ /// If the channel is full and not disconnected, this call will block until the send operation
+ /// can proceed. If the channel becomes disconnected, this call will wake up and return an
+ /// error. The returned error contains the original message.
+ ///
+ /// If called on a zero-capacity channel, this method will wait for a receive operation to
+ /// appear on the other side of the channel.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::Duration;
+ /// use crossbeam_channel::{bounded, SendError};
+ ///
+ /// let (s, r) = bounded(1);
+ /// assert_eq!(s.send(1), Ok(()));
+ ///
+ /// thread::spawn(move || {
+ /// assert_eq!(r.recv(), Ok(1));
+ /// thread::sleep(Duration::from_secs(1));
+ /// drop(r);
+ /// });
+ ///
+ /// assert_eq!(s.send(2), Ok(()));
+ /// assert_eq!(s.send(3), Err(SendError(3)));
+ /// ```
+ pub fn send(&self, msg: T) -> Result<(), SendError<T>> {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.send(msg, None),
+ SenderFlavor::List(chan) => chan.send(msg, None),
+ SenderFlavor::Zero(chan) => chan.send(msg, None),
+ }
+ .map_err(|err| match err {
+ SendTimeoutError::Disconnected(msg) => SendError(msg),
+ SendTimeoutError::Timeout(_) => unreachable!(),
+ })
+ }
+
+ /// Waits for a message to be sent into the channel, but only for a limited time.
+ ///
+ /// If the channel is full and not disconnected, this call will block until the send operation
+ /// can proceed or the operation times out. If the channel becomes disconnected, this call will
+ /// wake up and return an error. The returned error contains the original message.
+ ///
+ /// If called on a zero-capacity channel, this method will wait for a receive operation to
+ /// appear on the other side of the channel.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::Duration;
+ /// use crossbeam_channel::{bounded, SendTimeoutError};
+ ///
+ /// let (s, r) = bounded(0);
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_secs(1));
+ /// assert_eq!(r.recv(), Ok(2));
+ /// drop(r);
+ /// });
+ ///
+ /// assert_eq!(
+ /// s.send_timeout(1, Duration::from_millis(500)),
+ /// Err(SendTimeoutError::Timeout(1)),
+ /// );
+ /// assert_eq!(
+ /// s.send_timeout(2, Duration::from_secs(1)),
+ /// Ok(()),
+ /// );
+ /// assert_eq!(
+ /// s.send_timeout(3, Duration::from_millis(500)),
+ /// Err(SendTimeoutError::Disconnected(3)),
+ /// );
+ /// ```
+ pub fn send_timeout(&self, msg: T, timeout: Duration) -> Result<(), SendTimeoutError<T>> {
+ self.send_deadline(msg, Instant::now() + timeout)
+ }
+
+ /// Waits for a message to be sent into the channel, but only until a given deadline.
+ ///
+ /// If the channel is full and not disconnected, this call will block until the send operation
+ /// can proceed or the operation times out. If the channel becomes disconnected, this call will
+ /// wake up and return an error. The returned error contains the original message.
+ ///
+ /// If called on a zero-capacity channel, this method will wait for a receive operation to
+ /// appear on the other side of the channel.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::{Duration, Instant};
+ /// use crossbeam_channel::{bounded, SendTimeoutError};
+ ///
+ /// let (s, r) = bounded(0);
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_secs(1));
+ /// assert_eq!(r.recv(), Ok(2));
+ /// drop(r);
+ /// });
+ ///
+ /// let now = Instant::now();
+ ///
+ /// assert_eq!(
+ /// s.send_deadline(1, now + Duration::from_millis(500)),
+ /// Err(SendTimeoutError::Timeout(1)),
+ /// );
+ /// assert_eq!(
+ /// s.send_deadline(2, now + Duration::from_millis(1500)),
+ /// Ok(()),
+ /// );
+ /// assert_eq!(
+ /// s.send_deadline(3, now + Duration::from_millis(2000)),
+ /// Err(SendTimeoutError::Disconnected(3)),
+ /// );
+ /// ```
+ pub fn send_deadline(&self, msg: T, deadline: Instant) -> Result<(), SendTimeoutError<T>> {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.send(msg, Some(deadline)),
+ SenderFlavor::List(chan) => chan.send(msg, Some(deadline)),
+ SenderFlavor::Zero(chan) => chan.send(msg, Some(deadline)),
+ }
+ }
+
+ /// Returns `true` if the channel is empty.
+ ///
+ /// Note: Zero-capacity channels are always empty.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::unbounded;
+ ///
+ /// let (s, r) = unbounded();
+ /// assert!(s.is_empty());
+ ///
+ /// s.send(0).unwrap();
+ /// assert!(!s.is_empty());
+ /// ```
+ pub fn is_empty(&self) -> bool {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.is_empty(),
+ SenderFlavor::List(chan) => chan.is_empty(),
+ SenderFlavor::Zero(chan) => chan.is_empty(),
+ }
+ }
+
+ /// Returns `true` if the channel is full.
+ ///
+ /// Note: Zero-capacity channels are always full.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::bounded;
+ ///
+ /// let (s, r) = bounded(1);
+ ///
+ /// assert!(!s.is_full());
+ /// s.send(0).unwrap();
+ /// assert!(s.is_full());
+ /// ```
+ pub fn is_full(&self) -> bool {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.is_full(),
+ SenderFlavor::List(chan) => chan.is_full(),
+ SenderFlavor::Zero(chan) => chan.is_full(),
+ }
+ }
+
+ /// Returns the number of messages in the channel.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::unbounded;
+ ///
+ /// let (s, r) = unbounded();
+ /// assert_eq!(s.len(), 0);
+ ///
+ /// s.send(1).unwrap();
+ /// s.send(2).unwrap();
+ /// assert_eq!(s.len(), 2);
+ /// ```
+ pub fn len(&self) -> usize {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.len(),
+ SenderFlavor::List(chan) => chan.len(),
+ SenderFlavor::Zero(chan) => chan.len(),
+ }
+ }
+
+ /// If the channel is bounded, returns its capacity.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::{bounded, unbounded};
+ ///
+ /// let (s, _) = unbounded::<i32>();
+ /// assert_eq!(s.capacity(), None);
+ ///
+ /// let (s, _) = bounded::<i32>(5);
+ /// assert_eq!(s.capacity(), Some(5));
+ ///
+ /// let (s, _) = bounded::<i32>(0);
+ /// assert_eq!(s.capacity(), Some(0));
+ /// ```
+ pub fn capacity(&self) -> Option<usize> {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.capacity(),
+ SenderFlavor::List(chan) => chan.capacity(),
+ SenderFlavor::Zero(chan) => chan.capacity(),
+ }
+ }
+
+ /// Returns `true` if senders belong to the same channel.
+ ///
+ /// # Examples
+ ///
+ /// ```rust
+ /// use crossbeam_channel::unbounded;
+ ///
+ /// let (s, _) = unbounded::<usize>();
+ ///
+ /// let s2 = s.clone();
+ /// assert!(s.same_channel(&s2));
+ ///
+ /// let (s3, _) = unbounded();
+ /// assert!(!s.same_channel(&s3));
+ /// ```
+ pub fn same_channel(&self, other: &Sender<T>) -> bool {
+ match (&self.flavor, &other.flavor) {
+ (SenderFlavor::Array(ref a), SenderFlavor::Array(ref b)) => a == b,
+ (SenderFlavor::List(ref a), SenderFlavor::List(ref b)) => a == b,
+ (SenderFlavor::Zero(ref a), SenderFlavor::Zero(ref b)) => a == b,
+ _ => false,
+ }
+ }
+}
+
+impl<T> Drop for Sender<T> {
+ fn drop(&mut self) {
+ unsafe {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.release(|c| c.disconnect()),
+ SenderFlavor::List(chan) => chan.release(|c| c.disconnect()),
+ SenderFlavor::Zero(chan) => chan.release(|c| c.disconnect()),
+ }
+ }
+ }
+}
+
+impl<T> Clone for Sender<T> {
+ fn clone(&self) -> Self {
+ let flavor = match &self.flavor {
+ SenderFlavor::Array(chan) => SenderFlavor::Array(chan.acquire()),
+ SenderFlavor::List(chan) => SenderFlavor::List(chan.acquire()),
+ SenderFlavor::Zero(chan) => SenderFlavor::Zero(chan.acquire()),
+ };
+
+ Sender { flavor }
+ }
+}
+
+impl<T> fmt::Debug for Sender<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.pad("Sender { .. }")
+ }
+}
+
+/// The receiving side of a channel.
+///
+/// # Examples
+///
+/// ```
+/// use std::thread;
+/// use std::time::Duration;
+/// use crossbeam_channel::unbounded;
+///
+/// let (s, r) = unbounded();
+///
+/// thread::spawn(move || {
+/// let _ = s.send(1);
+/// thread::sleep(Duration::from_secs(1));
+/// let _ = s.send(2);
+/// });
+///
+/// assert_eq!(r.recv(), Ok(1)); // Received immediately.
+/// assert_eq!(r.recv(), Ok(2)); // Received after 1 second.
+/// ```
+pub struct Receiver<T> {
+ flavor: ReceiverFlavor<T>,
+}
+
+/// Receiver flavors.
+enum ReceiverFlavor<T> {
+ /// Bounded channel based on a preallocated array.
+ Array(counter::Receiver<flavors::array::Channel<T>>),
+
+ /// Unbounded channel implemented as a linked list.
+ List(counter::Receiver<flavors::list::Channel<T>>),
+
+ /// Zero-capacity channel.
+ Zero(counter::Receiver<flavors::zero::Channel<T>>),
+
+ /// The after flavor.
+ At(Arc<flavors::at::Channel>),
+
+ /// The tick flavor.
+ Tick(Arc<flavors::tick::Channel>),
+
+ /// The never flavor.
+ Never(flavors::never::Channel<T>),
+}
+
+unsafe impl<T: Send> Send for Receiver<T> {}
+unsafe impl<T: Send> Sync for Receiver<T> {}
+
+impl<T> UnwindSafe for Receiver<T> {}
+impl<T> RefUnwindSafe for Receiver<T> {}
+
+impl<T> Receiver<T> {
+ /// Attempts to receive a message from the channel without blocking.
+ ///
+ /// This method will either receive a message from the channel immediately or return an error
+ /// if the channel is empty.
+ ///
+ /// If called on a zero-capacity channel, this method will receive a message only if there
+ /// happens to be a send operation on the other side of the channel at the same time.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::{unbounded, TryRecvError};
+ ///
+ /// let (s, r) = unbounded();
+ /// assert_eq!(r.try_recv(), Err(TryRecvError::Empty));
+ ///
+ /// s.send(5).unwrap();
+ /// drop(s);
+ ///
+ /// assert_eq!(r.try_recv(), Ok(5));
+ /// assert_eq!(r.try_recv(), Err(TryRecvError::Disconnected));
+ /// ```
+ pub fn try_recv(&self) -> Result<T, TryRecvError> {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.try_recv(),
+ ReceiverFlavor::List(chan) => chan.try_recv(),
+ ReceiverFlavor::Zero(chan) => chan.try_recv(),
+ ReceiverFlavor::At(chan) => {
+ let msg = chan.try_recv();
+ unsafe {
+ mem::transmute_copy::<Result<Instant, TryRecvError>, Result<T, TryRecvError>>(
+ &msg,
+ )
+ }
+ }
+ ReceiverFlavor::Tick(chan) => {
+ let msg = chan.try_recv();
+ unsafe {
+ mem::transmute_copy::<Result<Instant, TryRecvError>, Result<T, TryRecvError>>(
+ &msg,
+ )
+ }
+ }
+ ReceiverFlavor::Never(chan) => chan.try_recv(),
+ }
+ }
+
+ /// Blocks the current thread until a message is received or the channel is empty and
+ /// disconnected.
+ ///
+ /// If the channel is empty and not disconnected, this call will block until the receive
+ /// operation can proceed. If the channel is empty and becomes disconnected, this call will
+ /// wake up and return an error.
+ ///
+ /// If called on a zero-capacity channel, this method will wait for a send operation to appear
+ /// on the other side of the channel.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::Duration;
+ /// use crossbeam_channel::{unbounded, RecvError};
+ ///
+ /// let (s, r) = unbounded();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_secs(1));
+ /// s.send(5).unwrap();
+ /// drop(s);
+ /// });
+ ///
+ /// assert_eq!(r.recv(), Ok(5));
+ /// assert_eq!(r.recv(), Err(RecvError));
+ /// ```
+ pub fn recv(&self) -> Result<T, RecvError> {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.recv(None),
+ ReceiverFlavor::List(chan) => chan.recv(None),
+ ReceiverFlavor::Zero(chan) => chan.recv(None),
+ ReceiverFlavor::At(chan) => {
+ let msg = chan.recv(None);
+ unsafe {
+ mem::transmute_copy::<
+ Result<Instant, RecvTimeoutError>,
+ Result<T, RecvTimeoutError>,
+ >(&msg)
+ }
+ }
+ ReceiverFlavor::Tick(chan) => {
+ let msg = chan.recv(None);
+ unsafe {
+ mem::transmute_copy::<
+ Result<Instant, RecvTimeoutError>,
+ Result<T, RecvTimeoutError>,
+ >(&msg)
+ }
+ }
+ ReceiverFlavor::Never(chan) => chan.recv(None),
+ }
+ .map_err(|_| RecvError)
+ }
+
+ /// Waits for a message to be received from the channel, but only for a limited time.
+ ///
+ /// If the channel is empty and not disconnected, this call will block until the receive
+ /// operation can proceed or the operation times out. If the channel is empty and becomes
+ /// disconnected, this call will wake up and return an error.
+ ///
+ /// If called on a zero-capacity channel, this method will wait for a send operation to appear
+ /// on the other side of the channel.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::Duration;
+ /// use crossbeam_channel::{unbounded, RecvTimeoutError};
+ ///
+ /// let (s, r) = unbounded();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_secs(1));
+ /// s.send(5).unwrap();
+ /// drop(s);
+ /// });
+ ///
+ /// assert_eq!(
+ /// r.recv_timeout(Duration::from_millis(500)),
+ /// Err(RecvTimeoutError::Timeout),
+ /// );
+ /// assert_eq!(
+ /// r.recv_timeout(Duration::from_secs(1)),
+ /// Ok(5),
+ /// );
+ /// assert_eq!(
+ /// r.recv_timeout(Duration::from_secs(1)),
+ /// Err(RecvTimeoutError::Disconnected),
+ /// );
+ /// ```
+ pub fn recv_timeout(&self, timeout: Duration) -> Result<T, RecvTimeoutError> {
+ self.recv_deadline(Instant::now() + timeout)
+ }
+
+ /// Waits for a message to be received from the channel, but only before a given deadline.
+ ///
+ /// If the channel is empty and not disconnected, this call will block until the receive
+ /// operation can proceed or the operation times out. If the channel is empty and becomes
+ /// disconnected, this call will wake up and return an error.
+ ///
+ /// If called on a zero-capacity channel, this method will wait for a send operation to appear
+ /// on the other side of the channel.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::{Instant, Duration};
+ /// use crossbeam_channel::{unbounded, RecvTimeoutError};
+ ///
+ /// let (s, r) = unbounded();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_secs(1));
+ /// s.send(5).unwrap();
+ /// drop(s);
+ /// });
+ ///
+ /// let now = Instant::now();
+ ///
+ /// assert_eq!(
+ /// r.recv_deadline(now + Duration::from_millis(500)),
+ /// Err(RecvTimeoutError::Timeout),
+ /// );
+ /// assert_eq!(
+ /// r.recv_deadline(now + Duration::from_millis(1500)),
+ /// Ok(5),
+ /// );
+ /// assert_eq!(
+ /// r.recv_deadline(now + Duration::from_secs(5)),
+ /// Err(RecvTimeoutError::Disconnected),
+ /// );
+ /// ```
+ pub fn recv_deadline(&self, deadline: Instant) -> Result<T, RecvTimeoutError> {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.recv(Some(deadline)),
+ ReceiverFlavor::List(chan) => chan.recv(Some(deadline)),
+ ReceiverFlavor::Zero(chan) => chan.recv(Some(deadline)),
+ ReceiverFlavor::At(chan) => {
+ let msg = chan.recv(Some(deadline));
+ unsafe {
+ mem::transmute_copy::<
+ Result<Instant, RecvTimeoutError>,
+ Result<T, RecvTimeoutError>,
+ >(&msg)
+ }
+ }
+ ReceiverFlavor::Tick(chan) => {
+ let msg = chan.recv(Some(deadline));
+ unsafe {
+ mem::transmute_copy::<
+ Result<Instant, RecvTimeoutError>,
+ Result<T, RecvTimeoutError>,
+ >(&msg)
+ }
+ }
+ ReceiverFlavor::Never(chan) => chan.recv(Some(deadline)),
+ }
+ }
+
+ /// Returns `true` if the channel is empty.
+ ///
+ /// Note: Zero-capacity channels are always empty.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::unbounded;
+ ///
+ /// let (s, r) = unbounded();
+ ///
+ /// assert!(r.is_empty());
+ /// s.send(0).unwrap();
+ /// assert!(!r.is_empty());
+ /// ```
+ pub fn is_empty(&self) -> bool {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.is_empty(),
+ ReceiverFlavor::List(chan) => chan.is_empty(),
+ ReceiverFlavor::Zero(chan) => chan.is_empty(),
+ ReceiverFlavor::At(chan) => chan.is_empty(),
+ ReceiverFlavor::Tick(chan) => chan.is_empty(),
+ ReceiverFlavor::Never(chan) => chan.is_empty(),
+ }
+ }
+
+ /// Returns `true` if the channel is full.
+ ///
+ /// Note: Zero-capacity channels are always full.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::bounded;
+ ///
+ /// let (s, r) = bounded(1);
+ ///
+ /// assert!(!r.is_full());
+ /// s.send(0).unwrap();
+ /// assert!(r.is_full());
+ /// ```
+ pub fn is_full(&self) -> bool {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.is_full(),
+ ReceiverFlavor::List(chan) => chan.is_full(),
+ ReceiverFlavor::Zero(chan) => chan.is_full(),
+ ReceiverFlavor::At(chan) => chan.is_full(),
+ ReceiverFlavor::Tick(chan) => chan.is_full(),
+ ReceiverFlavor::Never(chan) => chan.is_full(),
+ }
+ }
+
+ /// Returns the number of messages in the channel.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::unbounded;
+ ///
+ /// let (s, r) = unbounded();
+ /// assert_eq!(r.len(), 0);
+ ///
+ /// s.send(1).unwrap();
+ /// s.send(2).unwrap();
+ /// assert_eq!(r.len(), 2);
+ /// ```
+ pub fn len(&self) -> usize {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.len(),
+ ReceiverFlavor::List(chan) => chan.len(),
+ ReceiverFlavor::Zero(chan) => chan.len(),
+ ReceiverFlavor::At(chan) => chan.len(),
+ ReceiverFlavor::Tick(chan) => chan.len(),
+ ReceiverFlavor::Never(chan) => chan.len(),
+ }
+ }
+
+ /// If the channel is bounded, returns its capacity.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::{bounded, unbounded};
+ ///
+ /// let (_, r) = unbounded::<i32>();
+ /// assert_eq!(r.capacity(), None);
+ ///
+ /// let (_, r) = bounded::<i32>(5);
+ /// assert_eq!(r.capacity(), Some(5));
+ ///
+ /// let (_, r) = bounded::<i32>(0);
+ /// assert_eq!(r.capacity(), Some(0));
+ /// ```
+ pub fn capacity(&self) -> Option<usize> {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.capacity(),
+ ReceiverFlavor::List(chan) => chan.capacity(),
+ ReceiverFlavor::Zero(chan) => chan.capacity(),
+ ReceiverFlavor::At(chan) => chan.capacity(),
+ ReceiverFlavor::Tick(chan) => chan.capacity(),
+ ReceiverFlavor::Never(chan) => chan.capacity(),
+ }
+ }
+
+ /// A blocking iterator over messages in the channel.
+ ///
+ /// Each call to [`next`] blocks waiting for the next message and then returns it. However, if
+ /// the channel becomes empty and disconnected, it returns [`None`] without blocking.
+ ///
+ /// [`next`]: Iterator::next
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use crossbeam_channel::unbounded;
+ ///
+ /// let (s, r) = unbounded();
+ ///
+ /// thread::spawn(move || {
+ /// s.send(1).unwrap();
+ /// s.send(2).unwrap();
+ /// s.send(3).unwrap();
+ /// drop(s); // Disconnect the channel.
+ /// });
+ ///
+ /// // Collect all messages from the channel.
+ /// // Note that the call to `collect` blocks until the sender is dropped.
+ /// let v: Vec<_> = r.iter().collect();
+ ///
+ /// assert_eq!(v, [1, 2, 3]);
+ /// ```
+ pub fn iter(&self) -> Iter<'_, T> {
+ Iter { receiver: self }
+ }
+
+ /// A non-blocking iterator over messages in the channel.
+ ///
+ /// Each call to [`next`] returns a message if there is one ready to be received. The iterator
+ /// never blocks waiting for the next message.
+ ///
+ /// [`next`]: Iterator::next
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::Duration;
+ /// use crossbeam_channel::unbounded;
+ ///
+ /// let (s, r) = unbounded::<i32>();
+ ///
+ /// thread::spawn(move || {
+ /// s.send(1).unwrap();
+ /// thread::sleep(Duration::from_secs(1));
+ /// s.send(2).unwrap();
+ /// thread::sleep(Duration::from_secs(2));
+ /// s.send(3).unwrap();
+ /// });
+ ///
+ /// thread::sleep(Duration::from_secs(2));
+ ///
+ /// // Collect all messages from the channel without blocking.
+ /// // The third message hasn't been sent yet so we'll collect only the first two.
+ /// let v: Vec<_> = r.try_iter().collect();
+ ///
+ /// assert_eq!(v, [1, 2]);
+ /// ```
+ pub fn try_iter(&self) -> TryIter<'_, T> {
+ TryIter { receiver: self }
+ }
+
+ /// Returns `true` if receivers belong to the same channel.
+ ///
+ /// # Examples
+ ///
+ /// ```rust
+ /// use crossbeam_channel::unbounded;
+ ///
+ /// let (_, r) = unbounded::<usize>();
+ ///
+ /// let r2 = r.clone();
+ /// assert!(r.same_channel(&r2));
+ ///
+ /// let (_, r3) = unbounded();
+ /// assert!(!r.same_channel(&r3));
+ /// ```
+ pub fn same_channel(&self, other: &Receiver<T>) -> bool {
+ match (&self.flavor, &other.flavor) {
+ (ReceiverFlavor::Array(a), ReceiverFlavor::Array(b)) => a == b,
+ (ReceiverFlavor::List(a), ReceiverFlavor::List(b)) => a == b,
+ (ReceiverFlavor::Zero(a), ReceiverFlavor::Zero(b)) => a == b,
+ (ReceiverFlavor::At(a), ReceiverFlavor::At(b)) => Arc::ptr_eq(a, b),
+ (ReceiverFlavor::Tick(a), ReceiverFlavor::Tick(b)) => Arc::ptr_eq(a, b),
+ (ReceiverFlavor::Never(_), ReceiverFlavor::Never(_)) => true,
+ _ => false,
+ }
+ }
+}
+
+impl<T> Drop for Receiver<T> {
+ fn drop(&mut self) {
+ unsafe {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.release(|c| c.disconnect()),
+ ReceiverFlavor::List(chan) => chan.release(|c| c.disconnect()),
+ ReceiverFlavor::Zero(chan) => chan.release(|c| c.disconnect()),
+ ReceiverFlavor::At(_) => {}
+ ReceiverFlavor::Tick(_) => {}
+ ReceiverFlavor::Never(_) => {}
+ }
+ }
+ }
+}
+
+impl<T> Clone for Receiver<T> {
+ fn clone(&self) -> Self {
+ let flavor = match &self.flavor {
+ ReceiverFlavor::Array(chan) => ReceiverFlavor::Array(chan.acquire()),
+ ReceiverFlavor::List(chan) => ReceiverFlavor::List(chan.acquire()),
+ ReceiverFlavor::Zero(chan) => ReceiverFlavor::Zero(chan.acquire()),
+ ReceiverFlavor::At(chan) => ReceiverFlavor::At(chan.clone()),
+ ReceiverFlavor::Tick(chan) => ReceiverFlavor::Tick(chan.clone()),
+ ReceiverFlavor::Never(_) => ReceiverFlavor::Never(flavors::never::Channel::new()),
+ };
+
+ Receiver { flavor }
+ }
+}
+
+impl<T> fmt::Debug for Receiver<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.pad("Receiver { .. }")
+ }
+}
+
+impl<'a, T> IntoIterator for &'a Receiver<T> {
+ type Item = T;
+ type IntoIter = Iter<'a, T>;
+
+ fn into_iter(self) -> Self::IntoIter {
+ self.iter()
+ }
+}
+
+impl<T> IntoIterator for Receiver<T> {
+ type Item = T;
+ type IntoIter = IntoIter<T>;
+
+ fn into_iter(self) -> Self::IntoIter {
+ IntoIter { receiver: self }
+ }
+}
+
+/// A blocking iterator over messages in a channel.
+///
+/// Each call to [`next`] blocks waiting for the next message and then returns it. However, if the
+/// channel becomes empty and disconnected, it returns [`None`] without blocking.
+///
+/// [`next`]: Iterator::next
+///
+/// # Examples
+///
+/// ```
+/// use std::thread;
+/// use crossbeam_channel::unbounded;
+///
+/// let (s, r) = unbounded();
+///
+/// thread::spawn(move || {
+/// s.send(1).unwrap();
+/// s.send(2).unwrap();
+/// s.send(3).unwrap();
+/// drop(s); // Disconnect the channel.
+/// });
+///
+/// // Collect all messages from the channel.
+/// // Note that the call to `collect` blocks until the sender is dropped.
+/// let v: Vec<_> = r.iter().collect();
+///
+/// assert_eq!(v, [1, 2, 3]);
+/// ```
+pub struct Iter<'a, T> {
+ receiver: &'a Receiver<T>,
+}
+
+impl<T> FusedIterator for Iter<'_, T> {}
+
+impl<T> Iterator for Iter<'_, T> {
+ type Item = T;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ self.receiver.recv().ok()
+ }
+}
+
+impl<T> fmt::Debug for Iter<'_, T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.pad("Iter { .. }")
+ }
+}
+
+/// A non-blocking iterator over messages in a channel.
+///
+/// Each call to [`next`] returns a message if there is one ready to be received. The iterator
+/// never blocks waiting for the next message.
+///
+/// [`next`]: Iterator::next
+///
+/// # Examples
+///
+/// ```
+/// use std::thread;
+/// use std::time::Duration;
+/// use crossbeam_channel::unbounded;
+///
+/// let (s, r) = unbounded::<i32>();
+///
+/// thread::spawn(move || {
+/// s.send(1).unwrap();
+/// thread::sleep(Duration::from_secs(1));
+/// s.send(2).unwrap();
+/// thread::sleep(Duration::from_secs(2));
+/// s.send(3).unwrap();
+/// });
+///
+/// thread::sleep(Duration::from_secs(2));
+///
+/// // Collect all messages from the channel without blocking.
+/// // The third message hasn't been sent yet so we'll collect only the first two.
+/// let v: Vec<_> = r.try_iter().collect();
+///
+/// assert_eq!(v, [1, 2]);
+/// ```
+pub struct TryIter<'a, T> {
+ receiver: &'a Receiver<T>,
+}
+
+impl<T> Iterator for TryIter<'_, T> {
+ type Item = T;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ self.receiver.try_recv().ok()
+ }
+}
+
+impl<T> fmt::Debug for TryIter<'_, T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.pad("TryIter { .. }")
+ }
+}
+
+/// A blocking iterator over messages in a channel.
+///
+/// Each call to [`next`] blocks waiting for the next message and then returns it. However, if the
+/// channel becomes empty and disconnected, it returns [`None`] without blocking.
+///
+/// [`next`]: Iterator::next
+///
+/// # Examples
+///
+/// ```
+/// use std::thread;
+/// use crossbeam_channel::unbounded;
+///
+/// let (s, r) = unbounded();
+///
+/// thread::spawn(move || {
+/// s.send(1).unwrap();
+/// s.send(2).unwrap();
+/// s.send(3).unwrap();
+/// drop(s); // Disconnect the channel.
+/// });
+///
+/// // Collect all messages from the channel.
+/// // Note that the call to `collect` blocks until the sender is dropped.
+/// let v: Vec<_> = r.into_iter().collect();
+///
+/// assert_eq!(v, [1, 2, 3]);
+/// ```
+pub struct IntoIter<T> {
+ receiver: Receiver<T>,
+}
+
+impl<T> FusedIterator for IntoIter<T> {}
+
+impl<T> Iterator for IntoIter<T> {
+ type Item = T;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ self.receiver.recv().ok()
+ }
+}
+
+impl<T> fmt::Debug for IntoIter<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.pad("IntoIter { .. }")
+ }
+}
+
+impl<T> SelectHandle for Sender<T> {
+ fn try_select(&self, token: &mut Token) -> bool {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.sender().try_select(token),
+ SenderFlavor::List(chan) => chan.sender().try_select(token),
+ SenderFlavor::Zero(chan) => chan.sender().try_select(token),
+ }
+ }
+
+ fn deadline(&self) -> Option<Instant> {
+ None
+ }
+
+ fn register(&self, oper: Operation, cx: &Context) -> bool {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.sender().register(oper, cx),
+ SenderFlavor::List(chan) => chan.sender().register(oper, cx),
+ SenderFlavor::Zero(chan) => chan.sender().register(oper, cx),
+ }
+ }
+
+ fn unregister(&self, oper: Operation) {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.sender().unregister(oper),
+ SenderFlavor::List(chan) => chan.sender().unregister(oper),
+ SenderFlavor::Zero(chan) => chan.sender().unregister(oper),
+ }
+ }
+
+ fn accept(&self, token: &mut Token, cx: &Context) -> bool {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.sender().accept(token, cx),
+ SenderFlavor::List(chan) => chan.sender().accept(token, cx),
+ SenderFlavor::Zero(chan) => chan.sender().accept(token, cx),
+ }
+ }
+
+ fn is_ready(&self) -> bool {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.sender().is_ready(),
+ SenderFlavor::List(chan) => chan.sender().is_ready(),
+ SenderFlavor::Zero(chan) => chan.sender().is_ready(),
+ }
+ }
+
+ fn watch(&self, oper: Operation, cx: &Context) -> bool {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.sender().watch(oper, cx),
+ SenderFlavor::List(chan) => chan.sender().watch(oper, cx),
+ SenderFlavor::Zero(chan) => chan.sender().watch(oper, cx),
+ }
+ }
+
+ fn unwatch(&self, oper: Operation) {
+ match &self.flavor {
+ SenderFlavor::Array(chan) => chan.sender().unwatch(oper),
+ SenderFlavor::List(chan) => chan.sender().unwatch(oper),
+ SenderFlavor::Zero(chan) => chan.sender().unwatch(oper),
+ }
+ }
+}
+
+impl<T> SelectHandle for Receiver<T> {
+ fn try_select(&self, token: &mut Token) -> bool {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.receiver().try_select(token),
+ ReceiverFlavor::List(chan) => chan.receiver().try_select(token),
+ ReceiverFlavor::Zero(chan) => chan.receiver().try_select(token),
+ ReceiverFlavor::At(chan) => chan.try_select(token),
+ ReceiverFlavor::Tick(chan) => chan.try_select(token),
+ ReceiverFlavor::Never(chan) => chan.try_select(token),
+ }
+ }
+
+ fn deadline(&self) -> Option<Instant> {
+ match &self.flavor {
+ ReceiverFlavor::Array(_) => None,
+ ReceiverFlavor::List(_) => None,
+ ReceiverFlavor::Zero(_) => None,
+ ReceiverFlavor::At(chan) => chan.deadline(),
+ ReceiverFlavor::Tick(chan) => chan.deadline(),
+ ReceiverFlavor::Never(chan) => chan.deadline(),
+ }
+ }
+
+ fn register(&self, oper: Operation, cx: &Context) -> bool {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.receiver().register(oper, cx),
+ ReceiverFlavor::List(chan) => chan.receiver().register(oper, cx),
+ ReceiverFlavor::Zero(chan) => chan.receiver().register(oper, cx),
+ ReceiverFlavor::At(chan) => chan.register(oper, cx),
+ ReceiverFlavor::Tick(chan) => chan.register(oper, cx),
+ ReceiverFlavor::Never(chan) => chan.register(oper, cx),
+ }
+ }
+
+ fn unregister(&self, oper: Operation) {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.receiver().unregister(oper),
+ ReceiverFlavor::List(chan) => chan.receiver().unregister(oper),
+ ReceiverFlavor::Zero(chan) => chan.receiver().unregister(oper),
+ ReceiverFlavor::At(chan) => chan.unregister(oper),
+ ReceiverFlavor::Tick(chan) => chan.unregister(oper),
+ ReceiverFlavor::Never(chan) => chan.unregister(oper),
+ }
+ }
+
+ fn accept(&self, token: &mut Token, cx: &Context) -> bool {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.receiver().accept(token, cx),
+ ReceiverFlavor::List(chan) => chan.receiver().accept(token, cx),
+ ReceiverFlavor::Zero(chan) => chan.receiver().accept(token, cx),
+ ReceiverFlavor::At(chan) => chan.accept(token, cx),
+ ReceiverFlavor::Tick(chan) => chan.accept(token, cx),
+ ReceiverFlavor::Never(chan) => chan.accept(token, cx),
+ }
+ }
+
+ fn is_ready(&self) -> bool {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.receiver().is_ready(),
+ ReceiverFlavor::List(chan) => chan.receiver().is_ready(),
+ ReceiverFlavor::Zero(chan) => chan.receiver().is_ready(),
+ ReceiverFlavor::At(chan) => chan.is_ready(),
+ ReceiverFlavor::Tick(chan) => chan.is_ready(),
+ ReceiverFlavor::Never(chan) => chan.is_ready(),
+ }
+ }
+
+ fn watch(&self, oper: Operation, cx: &Context) -> bool {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.receiver().watch(oper, cx),
+ ReceiverFlavor::List(chan) => chan.receiver().watch(oper, cx),
+ ReceiverFlavor::Zero(chan) => chan.receiver().watch(oper, cx),
+ ReceiverFlavor::At(chan) => chan.watch(oper, cx),
+ ReceiverFlavor::Tick(chan) => chan.watch(oper, cx),
+ ReceiverFlavor::Never(chan) => chan.watch(oper, cx),
+ }
+ }
+
+ fn unwatch(&self, oper: Operation) {
+ match &self.flavor {
+ ReceiverFlavor::Array(chan) => chan.receiver().unwatch(oper),
+ ReceiverFlavor::List(chan) => chan.receiver().unwatch(oper),
+ ReceiverFlavor::Zero(chan) => chan.receiver().unwatch(oper),
+ ReceiverFlavor::At(chan) => chan.unwatch(oper),
+ ReceiverFlavor::Tick(chan) => chan.unwatch(oper),
+ ReceiverFlavor::Never(chan) => chan.unwatch(oper),
+ }
+ }
+}
+
+/// Writes a message into the channel.
+pub unsafe fn write<T>(s: &Sender<T>, token: &mut Token, msg: T) -> Result<(), T> {
+ match &s.flavor {
+ SenderFlavor::Array(chan) => chan.write(token, msg),
+ SenderFlavor::List(chan) => chan.write(token, msg),
+ SenderFlavor::Zero(chan) => chan.write(token, msg),
+ }
+}
+
+/// Reads a message from the channel.
+pub unsafe fn read<T>(r: &Receiver<T>, token: &mut Token) -> Result<T, ()> {
+ match &r.flavor {
+ ReceiverFlavor::Array(chan) => chan.read(token),
+ ReceiverFlavor::List(chan) => chan.read(token),
+ ReceiverFlavor::Zero(chan) => chan.read(token),
+ ReceiverFlavor::At(chan) => {
+ mem::transmute_copy::<Result<Instant, ()>, Result<T, ()>>(&chan.read(token))
+ }
+ ReceiverFlavor::Tick(chan) => {
+ mem::transmute_copy::<Result<Instant, ()>, Result<T, ()>>(&chan.read(token))
+ }
+ ReceiverFlavor::Never(chan) => chan.read(token),
+ }
+}
diff --git a/src/context.rs b/src/context.rs
new file mode 100644
index 0000000..e2e8480
--- /dev/null
+++ b/src/context.rs
@@ -0,0 +1,191 @@
+//! Thread-local context used in select.
+
+use std::cell::Cell;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::Arc;
+use std::thread::{self, Thread, ThreadId};
+use std::time::Instant;
+
+use crossbeam_utils::Backoff;
+
+use crate::select::Selected;
+
+/// Thread-local context used in select.
+#[derive(Debug, Clone)]
+pub struct Context {
+ inner: Arc<Inner>,
+}
+
+/// Inner representation of `Context`.
+#[derive(Debug)]
+struct Inner {
+ /// Selected operation.
+ select: AtomicUsize,
+
+ /// A slot into which another thread may store a pointer to its `Packet`.
+ packet: AtomicUsize,
+
+ /// Thread handle.
+ thread: Thread,
+
+ /// Thread id.
+ thread_id: ThreadId,
+}
+
+impl Context {
+ /// Creates a new context for the duration of the closure.
+ #[inline]
+ pub fn with<F, R>(f: F) -> R
+ where
+ F: FnOnce(&Context) -> R,
+ {
+ thread_local! {
+ /// Cached thread-local context.
+ static CONTEXT: Cell<Option<Context>> = Cell::new(Some(Context::new()));
+ }
+
+ let mut f = Some(f);
+ let mut f = move |cx: &Context| -> R {
+ let f = f.take().unwrap();
+ f(cx)
+ };
+
+ CONTEXT
+ .try_with(|cell| match cell.take() {
+ None => f(&Context::new()),
+ Some(cx) => {
+ cx.reset();
+ let res = f(&cx);
+ cell.set(Some(cx));
+ res
+ }
+ })
+ .unwrap_or_else(|_| f(&Context::new()))
+ }
+
+ /// Creates a new `Context`.
+ #[cold]
+ fn new() -> Context {
+ Context {
+ inner: Arc::new(Inner {
+ select: AtomicUsize::new(Selected::Waiting.into()),
+ packet: AtomicUsize::new(0),
+ thread: thread::current(),
+ thread_id: thread::current().id(),
+ }),
+ }
+ }
+
+ /// Resets `select` and `packet`.
+ #[inline]
+ fn reset(&self) {
+ self.inner
+ .select
+ .store(Selected::Waiting.into(), Ordering::Release);
+ self.inner.packet.store(0, Ordering::Release);
+ }
+
+ /// Attempts to select an operation.
+ ///
+ /// On failure, the previously selected operation is returned.
+ #[inline]
+ pub fn try_select(&self, select: Selected) -> Result<(), Selected> {
+ self.inner
+ .select
+ .compare_exchange(
+ Selected::Waiting.into(),
+ select.into(),
+ Ordering::AcqRel,
+ Ordering::Acquire,
+ )
+ .map(|_| ())
+ .map_err(|e| e.into())
+ }
+
+ /// Returns the selected operation.
+ #[inline]
+ pub fn selected(&self) -> Selected {
+ Selected::from(self.inner.select.load(Ordering::Acquire))
+ }
+
+ /// Stores a packet.
+ ///
+ /// This method must be called after `try_select` succeeds and there is a packet to provide.
+ #[inline]
+ pub fn store_packet(&self, packet: usize) {
+ if packet != 0 {
+ self.inner.packet.store(packet, Ordering::Release);
+ }
+ }
+
+ /// Waits until a packet is provided and returns it.
+ #[inline]
+ pub fn wait_packet(&self) -> usize {
+ let backoff = Backoff::new();
+ loop {
+ let packet = self.inner.packet.load(Ordering::Acquire);
+ if packet != 0 {
+ return packet;
+ }
+ backoff.snooze();
+ }
+ }
+
+ /// Waits until an operation is selected and returns it.
+ ///
+ /// If the deadline is reached, `Selected::Aborted` will be selected.
+ #[inline]
+ pub fn wait_until(&self, deadline: Option<Instant>) -> Selected {
+ // Spin for a short time, waiting until an operation is selected.
+ let backoff = Backoff::new();
+ loop {
+ let sel = Selected::from(self.inner.select.load(Ordering::Acquire));
+ if sel != Selected::Waiting {
+ return sel;
+ }
+
+ if backoff.is_completed() {
+ break;
+ } else {
+ backoff.snooze();
+ }
+ }
+
+ loop {
+ // Check whether an operation has been selected.
+ let sel = Selected::from(self.inner.select.load(Ordering::Acquire));
+ if sel != Selected::Waiting {
+ return sel;
+ }
+
+ // If there's a deadline, park the current thread until the deadline is reached.
+ if let Some(end) = deadline {
+ let now = Instant::now();
+
+ if now < end {
+ thread::park_timeout(end - now);
+ } else {
+ // The deadline has been reached. Try aborting select.
+ return match self.try_select(Selected::Aborted) {
+ Ok(()) => Selected::Aborted,
+ Err(s) => s,
+ };
+ }
+ } else {
+ thread::park();
+ }
+ }
+ }
+
+ /// Unparks the thread this context belongs to.
+ #[inline]
+ pub fn unpark(&self) {
+ self.inner.thread.unpark();
+ }
+
+ /// Returns the id of the thread this context belongs to.
+ #[inline]
+ pub fn thread_id(&self) -> ThreadId {
+ self.inner.thread_id
+ }
+}
diff --git a/src/counter.rs b/src/counter.rs
new file mode 100644
index 0000000..2eaf067
--- /dev/null
+++ b/src/counter.rs
@@ -0,0 +1,144 @@
+//! Reference counter for channels.
+
+use std::isize;
+use std::ops;
+use std::process;
+use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
+
+/// Reference counter internals.
+struct Counter<C> {
+ /// The number of senders associated with the channel.
+ senders: AtomicUsize,
+
+ /// The number of receivers associated with the channel.
+ receivers: AtomicUsize,
+
+ /// Set to `true` if the last sender or the last receiver reference deallocates the channel.
+ destroy: AtomicBool,
+
+ /// The internal channel.
+ chan: C,
+}
+
+/// Wraps a channel into the reference counter.
+pub fn new<C>(chan: C) -> (Sender<C>, Receiver<C>) {
+ let counter = Box::into_raw(Box::new(Counter {
+ senders: AtomicUsize::new(1),
+ receivers: AtomicUsize::new(1),
+ destroy: AtomicBool::new(false),
+ chan,
+ }));
+ let s = Sender { counter };
+ let r = Receiver { counter };
+ (s, r)
+}
+
+/// The sending side.
+pub struct Sender<C> {
+ counter: *mut Counter<C>,
+}
+
+impl<C> Sender<C> {
+ /// Returns the internal `Counter`.
+ fn counter(&self) -> &Counter<C> {
+ unsafe { &*self.counter }
+ }
+
+ /// Acquires another sender reference.
+ pub fn acquire(&self) -> Sender<C> {
+ let count = self.counter().senders.fetch_add(1, Ordering::Relaxed);
+
+ // Cloning senders and calling `mem::forget` on the clones could potentially overflow the
+ // counter. It's very difficult to recover sensibly from such degenerate scenarios so we
+ // just abort when the count becomes very large.
+ if count > isize::MAX as usize {
+ process::abort();
+ }
+
+ Sender {
+ counter: self.counter,
+ }
+ }
+
+ /// Releases the sender reference.
+ ///
+ /// Function `disconnect` will be called if this is the last sender reference.
+ pub unsafe fn release<F: FnOnce(&C) -> bool>(&self, disconnect: F) {
+ if self.counter().senders.fetch_sub(1, Ordering::AcqRel) == 1 {
+ disconnect(&self.counter().chan);
+
+ if self.counter().destroy.swap(true, Ordering::AcqRel) {
+ drop(Box::from_raw(self.counter));
+ }
+ }
+ }
+}
+
+impl<C> ops::Deref for Sender<C> {
+ type Target = C;
+
+ fn deref(&self) -> &C {
+ &self.counter().chan
+ }
+}
+
+impl<C> PartialEq for Sender<C> {
+ fn eq(&self, other: &Sender<C>) -> bool {
+ self.counter == other.counter
+ }
+}
+
+/// The receiving side.
+pub struct Receiver<C> {
+ counter: *mut Counter<C>,
+}
+
+impl<C> Receiver<C> {
+ /// Returns the internal `Counter`.
+ fn counter(&self) -> &Counter<C> {
+ unsafe { &*self.counter }
+ }
+
+ /// Acquires another receiver reference.
+ pub fn acquire(&self) -> Receiver<C> {
+ let count = self.counter().receivers.fetch_add(1, Ordering::Relaxed);
+
+ // Cloning receivers and calling `mem::forget` on the clones could potentially overflow the
+ // counter. It's very difficult to recover sensibly from such degenerate scenarios so we
+ // just abort when the count becomes very large.
+ if count > isize::MAX as usize {
+ process::abort();
+ }
+
+ Receiver {
+ counter: self.counter,
+ }
+ }
+
+ /// Releases the receiver reference.
+ ///
+ /// Function `disconnect` will be called if this is the last receiver reference.
+ pub unsafe fn release<F: FnOnce(&C) -> bool>(&self, disconnect: F) {
+ if self.counter().receivers.fetch_sub(1, Ordering::AcqRel) == 1 {
+ disconnect(&self.counter().chan);
+
+ if self.counter().destroy.swap(true, Ordering::AcqRel) {
+ drop(Box::from_raw(self.counter));
+ }
+ }
+ }
+}
+
+impl<C> ops::Deref for Receiver<C> {
+ type Target = C;
+
+ fn deref(&self) -> &C {
+ &self.counter().chan
+ }
+}
+
+impl<C> PartialEq for Receiver<C> {
+ fn eq(&self, other: &Receiver<C>) -> bool {
+ self.counter == other.counter
+ }
+}
diff --git a/src/err.rs b/src/err.rs
new file mode 100644
index 0000000..578acc6
--- /dev/null
+++ b/src/err.rs
@@ -0,0 +1,382 @@
+use std::error;
+use std::fmt;
+
+/// An error returned from the [`send`] method.
+///
+/// The message could not be sent because the channel is disconnected.
+///
+/// The error contains the message so it can be recovered.
+///
+/// [`send`]: super::Sender::send
+#[derive(PartialEq, Eq, Clone, Copy)]
+pub struct SendError<T>(pub T);
+
+/// An error returned from the [`try_send`] method.
+///
+/// The error contains the message being sent so it can be recovered.
+///
+/// [`try_send`]: super::Sender::try_send
+#[derive(PartialEq, Eq, Clone, Copy)]
+pub enum TrySendError<T> {
+ /// The message could not be sent because the channel is full.
+ ///
+ /// If this is a zero-capacity channel, then the error indicates that there was no receiver
+ /// available to receive the message at the time.
+ Full(T),
+
+ /// The message could not be sent because the channel is disconnected.
+ Disconnected(T),
+}
+
+/// An error returned from the [`send_timeout`] method.
+///
+/// The error contains the message being sent so it can be recovered.
+///
+/// [`send_timeout`]: super::Sender::send_timeout
+#[derive(PartialEq, Eq, Clone, Copy)]
+pub enum SendTimeoutError<T> {
+ /// The message could not be sent because the channel is full and the operation timed out.
+ ///
+ /// If this is a zero-capacity channel, then the error indicates that there was no receiver
+ /// available to receive the message and the operation timed out.
+ Timeout(T),
+
+ /// The message could not be sent because the channel is disconnected.
+ Disconnected(T),
+}
+
+/// An error returned from the [`recv`] method.
+///
+/// A message could not be received because the channel is empty and disconnected.
+///
+/// [`recv`]: super::Receiver::recv
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub struct RecvError;
+
+/// An error returned from the [`try_recv`] method.
+///
+/// [`try_recv`]: super::Receiver::try_recv
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub enum TryRecvError {
+ /// A message could not be received because the channel is empty.
+ ///
+ /// If this is a zero-capacity channel, then the error indicates that there was no sender
+ /// available to send a message at the time.
+ Empty,
+
+ /// The message could not be received because the channel is empty and disconnected.
+ Disconnected,
+}
+
+/// An error returned from the [`recv_timeout`] method.
+///
+/// [`recv_timeout`]: super::Receiver::recv_timeout
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub enum RecvTimeoutError {
+ /// A message could not be received because the channel is empty and the operation timed out.
+ ///
+ /// If this is a zero-capacity channel, then the error indicates that there was no sender
+ /// available to send a message and the operation timed out.
+ Timeout,
+
+ /// The message could not be received because the channel is empty and disconnected.
+ Disconnected,
+}
+
+/// An error returned from the [`try_select`] method.
+///
+/// Failed because none of the channel operations were ready.
+///
+/// [`try_select`]: super::Select::try_select
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub struct TrySelectError;
+
+/// An error returned from the [`select_timeout`] method.
+///
+/// Failed because none of the channel operations became ready before the timeout.
+///
+/// [`select_timeout`]: super::Select::select_timeout
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub struct SelectTimeoutError;
+
+/// An error returned from the [`try_ready`] method.
+///
+/// Failed because none of the channel operations were ready.
+///
+/// [`try_ready`]: super::Select::try_ready
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub struct TryReadyError;
+
+/// An error returned from the [`ready_timeout`] method.
+///
+/// Failed because none of the channel operations became ready before the timeout.
+///
+/// [`ready_timeout`]: super::Select::ready_timeout
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub struct ReadyTimeoutError;
+
+impl<T> fmt::Debug for SendError<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ "SendError(..)".fmt(f)
+ }
+}
+
+impl<T> fmt::Display for SendError<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ "sending on a disconnected channel".fmt(f)
+ }
+}
+
+impl<T: Send> error::Error for SendError<T> {}
+
+impl<T> SendError<T> {
+ /// Unwraps the message.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::unbounded;
+ ///
+ /// let (s, r) = unbounded();
+ /// drop(r);
+ ///
+ /// if let Err(err) = s.send("foo") {
+ /// assert_eq!(err.into_inner(), "foo");
+ /// }
+ /// ```
+ pub fn into_inner(self) -> T {
+ self.0
+ }
+}
+
+impl<T> fmt::Debug for TrySendError<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ match *self {
+ TrySendError::Full(..) => "Full(..)".fmt(f),
+ TrySendError::Disconnected(..) => "Disconnected(..)".fmt(f),
+ }
+ }
+}
+
+impl<T> fmt::Display for TrySendError<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ match *self {
+ TrySendError::Full(..) => "sending on a full channel".fmt(f),
+ TrySendError::Disconnected(..) => "sending on a disconnected channel".fmt(f),
+ }
+ }
+}
+
+impl<T: Send> error::Error for TrySendError<T> {}
+
+impl<T> From<SendError<T>> for TrySendError<T> {
+ fn from(err: SendError<T>) -> TrySendError<T> {
+ match err {
+ SendError(t) => TrySendError::Disconnected(t),
+ }
+ }
+}
+
+impl<T> TrySendError<T> {
+ /// Unwraps the message.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::bounded;
+ ///
+ /// let (s, r) = bounded(0);
+ ///
+ /// if let Err(err) = s.try_send("foo") {
+ /// assert_eq!(err.into_inner(), "foo");
+ /// }
+ /// ```
+ pub fn into_inner(self) -> T {
+ match self {
+ TrySendError::Full(v) => v,
+ TrySendError::Disconnected(v) => v,
+ }
+ }
+
+ /// Returns `true` if the send operation failed because the channel is full.
+ pub fn is_full(&self) -> bool {
+ match self {
+ TrySendError::Full(_) => true,
+ _ => false,
+ }
+ }
+
+ /// Returns `true` if the send operation failed because the channel is disconnected.
+ pub fn is_disconnected(&self) -> bool {
+ match self {
+ TrySendError::Disconnected(_) => true,
+ _ => false,
+ }
+ }
+}
+
+impl<T> fmt::Debug for SendTimeoutError<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ "SendTimeoutError(..)".fmt(f)
+ }
+}
+
+impl<T> fmt::Display for SendTimeoutError<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ match *self {
+ SendTimeoutError::Timeout(..) => "timed out waiting on send operation".fmt(f),
+ SendTimeoutError::Disconnected(..) => "sending on a disconnected channel".fmt(f),
+ }
+ }
+}
+
+impl<T: Send> error::Error for SendTimeoutError<T> {}
+
+impl<T> From<SendError<T>> for SendTimeoutError<T> {
+ fn from(err: SendError<T>) -> SendTimeoutError<T> {
+ match err {
+ SendError(e) => SendTimeoutError::Disconnected(e),
+ }
+ }
+}
+
+impl<T> SendTimeoutError<T> {
+ /// Unwraps the message.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::time::Duration;
+ /// use crossbeam_channel::unbounded;
+ ///
+ /// let (s, r) = unbounded();
+ ///
+ /// if let Err(err) = s.send_timeout("foo", Duration::from_secs(1)) {
+ /// assert_eq!(err.into_inner(), "foo");
+ /// }
+ /// ```
+ pub fn into_inner(self) -> T {
+ match self {
+ SendTimeoutError::Timeout(v) => v,
+ SendTimeoutError::Disconnected(v) => v,
+ }
+ }
+
+ /// Returns `true` if the send operation timed out.
+ pub fn is_timeout(&self) -> bool {
+ match self {
+ SendTimeoutError::Timeout(_) => true,
+ _ => false,
+ }
+ }
+
+ /// Returns `true` if the send operation failed because the channel is disconnected.
+ pub fn is_disconnected(&self) -> bool {
+ match self {
+ SendTimeoutError::Disconnected(_) => true,
+ _ => false,
+ }
+ }
+}
+
+impl fmt::Display for RecvError {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ "receiving on an empty and disconnected channel".fmt(f)
+ }
+}
+
+impl error::Error for RecvError {}
+
+impl fmt::Display for TryRecvError {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ match *self {
+ TryRecvError::Empty => "receiving on an empty channel".fmt(f),
+ TryRecvError::Disconnected => "receiving on an empty and disconnected channel".fmt(f),
+ }
+ }
+}
+
+impl error::Error for TryRecvError {}
+
+impl From<RecvError> for TryRecvError {
+ fn from(err: RecvError) -> TryRecvError {
+ match err {
+ RecvError => TryRecvError::Disconnected,
+ }
+ }
+}
+
+impl TryRecvError {
+ /// Returns `true` if the receive operation failed because the channel is empty.
+ #[allow(clippy::trivially_copy_pass_by_ref)]
+ pub fn is_empty(&self) -> bool {
+ match self {
+ TryRecvError::Empty => true,
+ _ => false,
+ }
+ }
+
+ /// Returns `true` if the receive operation failed because the channel is disconnected.
+ #[allow(clippy::trivially_copy_pass_by_ref)]
+ pub fn is_disconnected(&self) -> bool {
+ match self {
+ TryRecvError::Disconnected => true,
+ _ => false,
+ }
+ }
+}
+
+impl fmt::Display for RecvTimeoutError {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ match *self {
+ RecvTimeoutError::Timeout => "timed out waiting on receive operation".fmt(f),
+ RecvTimeoutError::Disconnected => "channel is empty and disconnected".fmt(f),
+ }
+ }
+}
+
+impl error::Error for RecvTimeoutError {}
+
+impl From<RecvError> for RecvTimeoutError {
+ fn from(err: RecvError) -> RecvTimeoutError {
+ match err {
+ RecvError => RecvTimeoutError::Disconnected,
+ }
+ }
+}
+
+impl RecvTimeoutError {
+ /// Returns `true` if the receive operation timed out.
+ #[allow(clippy::trivially_copy_pass_by_ref)]
+ pub fn is_timeout(&self) -> bool {
+ match self {
+ RecvTimeoutError::Timeout => true,
+ _ => false,
+ }
+ }
+
+ /// Returns `true` if the receive operation failed because the channel is disconnected.
+ #[allow(clippy::trivially_copy_pass_by_ref)]
+ pub fn is_disconnected(&self) -> bool {
+ match self {
+ RecvTimeoutError::Disconnected => true,
+ _ => false,
+ }
+ }
+}
+
+impl fmt::Display for TrySelectError {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ "all operations in select would block".fmt(f)
+ }
+}
+
+impl error::Error for TrySelectError {}
+
+impl fmt::Display for SelectTimeoutError {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ "timed out waiting on select".fmt(f)
+ }
+}
+
+impl error::Error for SelectTimeoutError {}
diff --git a/src/flavors/array.rs b/src/flavors/array.rs
new file mode 100644
index 0000000..323a200
--- /dev/null
+++ b/src/flavors/array.rs
@@ -0,0 +1,641 @@
+//! Bounded channel based on a preallocated array.
+//!
+//! This flavor has a fixed, positive capacity.
+//!
+//! The implementation is based on Dmitry Vyukov's bounded MPMC queue.
+//!
+//! Source:
+//! - http://www.1024cores.net/home/lock-free-algorithms/queues/bounded-mpmc-queue
+//! - https://docs.google.com/document/d/1yIAYmbvL3JxOKOjuCyon7JhW4cSv1wy5hC0ApeGMV9s/pub
+//!
+//! Copyright & License:
+//! - Copyright (c) 2010-2011 Dmitry Vyukov
+//! - Simplified BSD License and Apache License, Version 2.0
+//! - http://www.1024cores.net/home/code-license
+
+use std::cell::UnsafeCell;
+use std::marker::PhantomData;
+use std::mem::{self, MaybeUninit};
+use std::ptr;
+use std::sync::atomic::{self, AtomicUsize, Ordering};
+use std::time::Instant;
+
+use crossbeam_utils::{Backoff, CachePadded};
+
+use crate::context::Context;
+use crate::err::{RecvTimeoutError, SendTimeoutError, TryRecvError, TrySendError};
+use crate::select::{Operation, SelectHandle, Selected, Token};
+use crate::waker::SyncWaker;
+
+/// A slot in a channel.
+struct Slot<T> {
+ /// The current stamp.
+ stamp: AtomicUsize,
+
+ /// The message in this slot.
+ msg: UnsafeCell<MaybeUninit<T>>,
+}
+
+/// The token type for the array flavor.
+#[derive(Debug)]
+pub struct ArrayToken {
+ /// Slot to read from or write to.
+ slot: *const u8,
+
+ /// Stamp to store into the slot after reading or writing.
+ stamp: usize,
+}
+
+impl Default for ArrayToken {
+ #[inline]
+ fn default() -> Self {
+ ArrayToken {
+ slot: ptr::null(),
+ stamp: 0,
+ }
+ }
+}
+
+/// Bounded channel based on a preallocated array.
+pub 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: CachePadded<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: CachePadded<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 the channel is disconnected.
+ mark_bit: usize,
+
+ /// Senders waiting while the channel is full.
+ senders: SyncWaker,
+
+ /// Receivers waiting while the channel is empty and not disconnected.
+ receivers: SyncWaker,
+
+ /// Indicates that dropping a `Channel<T>` may drop values of type `T`.
+ _marker: PhantomData<T>,
+}
+
+impl<T> Channel<T> {
+ /// Creates a bounded channel of capacity `cap`.
+ pub 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 initialized
+ // with stamps.
+ let buffer = {
+ let mut boxed: Box<[Slot<T>]> = (0..cap)
+ .map(|i| {
+ // Set the stamp to `{ lap: 0, mark: 0, index: i }`.
+ Slot {
+ stamp: AtomicUsize::new(i),
+ msg: UnsafeCell::new(MaybeUninit::uninit()),
+ }
+ })
+ .collect();
+ let ptr = boxed.as_mut_ptr();
+ mem::forget(boxed);
+ ptr
+ };
+
+ Channel {
+ buffer,
+ cap,
+ one_lap,
+ mark_bit,
+ head: CachePadded::new(AtomicUsize::new(head)),
+ tail: CachePadded::new(AtomicUsize::new(tail)),
+ senders: SyncWaker::new(),
+ receivers: SyncWaker::new(),
+ _marker: PhantomData,
+ }
+ }
+
+ /// Returns a receiver handle to the channel.
+ pub fn receiver(&self) -> Receiver<'_, T> {
+ Receiver(self)
+ }
+
+ /// Returns a sender handle to the channel.
+ pub fn sender(&self) -> Sender<'_, T> {
+ Sender(self)
+ }
+
+ /// Attempts to reserve a slot for sending a message.
+ fn start_send(&self, token: &mut Token) -> bool {
+ let backoff = Backoff::new();
+ let mut tail = self.tail.load(Ordering::Relaxed);
+
+ loop {
+ // Check if the channel is disconnected.
+ if tail & self.mark_bit != 0 {
+ token.array.slot = ptr::null();
+ token.array.stamp = 0;
+ return true;
+ }
+
+ // 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,
+ new_tail,
+ Ordering::SeqCst,
+ Ordering::Relaxed,
+ ) {
+ Ok(_) => {
+ // Prepare the token for the follow-up call to `write`.
+ token.array.slot = slot as *const Slot<T> as *const u8;
+ token.array.stamp = tail + 1;
+ return true;
+ }
+ 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.
+ return false;
+ }
+
+ 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);
+ }
+ }
+ }
+
+ /// Writes a message into the channel.
+ pub unsafe fn write(&self, token: &mut Token, msg: T) -> Result<(), T> {
+ // If there is no slot, the channel is disconnected.
+ if token.array.slot.is_null() {
+ return Err(msg);
+ }
+
+ let slot: &Slot<T> = &*(token.array.slot as *const Slot<T>);
+
+ // Write the message into the slot and update the stamp.
+ slot.msg.get().write(MaybeUninit::new(msg));
+ slot.stamp.store(token.array.stamp, Ordering::Release);
+
+ // Wake a sleeping receiver.
+ self.receivers.notify();
+ Ok(())
+ }
+
+ /// Attempts to reserve a slot for receiving a message.
+ fn start_recv(&self, token: &mut Token) -> bool {
+ 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(_) => {
+ // Prepare the token for the follow-up call to `read`.
+ token.array.slot = slot as *const Slot<T> as *const u8;
+ token.array.stamp = head.wrapping_add(self.one_lap);
+ return true;
+ }
+ 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 {
+ // ...then receive an error.
+ token.array.slot = ptr::null();
+ token.array.stamp = 0;
+ return true;
+ } else {
+ // Otherwise, the receive operation is not ready.
+ return false;
+ }
+ }
+
+ 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);
+ }
+ }
+ }
+
+ /// Reads a message from the channel.
+ pub unsafe fn read(&self, token: &mut Token) -> Result<T, ()> {
+ if token.array.slot.is_null() {
+ // The channel is disconnected.
+ return Err(());
+ }
+
+ let slot: &Slot<T> = &*(token.array.slot as *const Slot<T>);
+
+ // Read the message from the slot and update the stamp.
+ let msg = slot.msg.get().read().assume_init();
+ slot.stamp.store(token.array.stamp, Ordering::Release);
+
+ // Wake a sleeping sender.
+ self.senders.notify();
+ Ok(msg)
+ }
+
+ /// Attempts to send a message into the channel.
+ pub fn try_send(&self, msg: T) -> Result<(), TrySendError<T>> {
+ let token = &mut Token::default();
+ if self.start_send(token) {
+ unsafe { self.write(token, msg).map_err(TrySendError::Disconnected) }
+ } else {
+ Err(TrySendError::Full(msg))
+ }
+ }
+
+ /// Sends a message into the channel.
+ pub fn send(&self, msg: T, deadline: Option<Instant>) -> Result<(), SendTimeoutError<T>> {
+ let token = &mut Token::default();
+ loop {
+ // Try sending a message several times.
+ let backoff = Backoff::new();
+ loop {
+ if self.start_send(token) {
+ let res = unsafe { self.write(token, msg) };
+ return res.map_err(SendTimeoutError::Disconnected);
+ }
+
+ if backoff.is_completed() {
+ break;
+ } else {
+ backoff.snooze();
+ }
+ }
+
+ if let Some(d) = deadline {
+ if Instant::now() >= d {
+ return Err(SendTimeoutError::Timeout(msg));
+ }
+ }
+
+ Context::with(|cx| {
+ // Prepare for blocking until a receiver wakes us up.
+ let oper = Operation::hook(token);
+ self.senders.register(oper, cx);
+
+ // Has the channel become ready just now?
+ if !self.is_full() || self.is_disconnected() {
+ let _ = cx.try_select(Selected::Aborted);
+ }
+
+ // Block the current thread.
+ let sel = cx.wait_until(deadline);
+
+ match sel {
+ Selected::Waiting => unreachable!(),
+ Selected::Aborted | Selected::Disconnected => {
+ self.senders.unregister(oper).unwrap();
+ }
+ Selected::Operation(_) => {}
+ }
+ });
+ }
+ }
+
+ /// Attempts to receive a message without blocking.
+ pub fn try_recv(&self) -> Result<T, TryRecvError> {
+ let token = &mut Token::default();
+
+ if self.start_recv(token) {
+ unsafe { self.read(token).map_err(|_| TryRecvError::Disconnected) }
+ } else {
+ Err(TryRecvError::Empty)
+ }
+ }
+
+ /// Receives a message from the channel.
+ pub fn recv(&self, deadline: Option<Instant>) -> Result<T, RecvTimeoutError> {
+ let token = &mut Token::default();
+ loop {
+ // Try receiving a message several times.
+ let backoff = Backoff::new();
+ loop {
+ if self.start_recv(token) {
+ let res = unsafe { self.read(token) };
+ return res.map_err(|_| RecvTimeoutError::Disconnected);
+ }
+
+ if backoff.is_completed() {
+ break;
+ } else {
+ backoff.snooze();
+ }
+ }
+
+ if let Some(d) = deadline {
+ if Instant::now() >= d {
+ return Err(RecvTimeoutError::Timeout);
+ }
+ }
+
+ Context::with(|cx| {
+ // Prepare for blocking until a sender wakes us up.
+ let oper = Operation::hook(token);
+ self.receivers.register(oper, cx);
+
+ // Has the channel become ready just now?
+ if !self.is_empty() || self.is_disconnected() {
+ let _ = cx.try_select(Selected::Aborted);
+ }
+
+ // Block the current thread.
+ let sel = cx.wait_until(deadline);
+
+ match sel {
+ Selected::Waiting => unreachable!(),
+ Selected::Aborted | Selected::Disconnected => {
+ self.receivers.unregister(oper).unwrap();
+ // If the channel was disconnected, we still have to check for remaining
+ // messages.
+ }
+ Selected::Operation(_) => {}
+ }
+ });
+ }
+ }
+
+ /// Returns the current number of messages inside the channel.
+ pub 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 the capacity of the channel.
+ pub fn capacity(&self) -> Option<usize> {
+ Some(self.cap)
+ }
+
+ /// Disconnects the channel and wakes up all blocked senders and receivers.
+ ///
+ /// Returns `true` if this call disconnected the channel.
+ pub fn disconnect(&self) -> bool {
+ let tail = self.tail.fetch_or(self.mark_bit, Ordering::SeqCst);
+
+ if tail & self.mark_bit == 0 {
+ self.senders.disconnect();
+ self.receivers.disconnect();
+ true
+ } else {
+ false
+ }
+ }
+
+ /// 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.
+ pub 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.
+ pub 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
+ }
+}
+
+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 {
+ let p = {
+ let slot = &mut *self.buffer.add(index);
+ let msg = &mut *slot.msg.get();
+ msg.as_mut_ptr()
+ };
+ p.drop_in_place();
+ }
+ }
+
+ // Finally, deallocate the buffer, but don't run any destructors.
+ unsafe {
+ // Create a slice from the buffer to make
+ // a fat pointer. Then, use Box::from_raw
+ // to deallocate it.
+ let ptr = std::slice::from_raw_parts_mut(self.buffer, self.cap) as *mut [Slot<T>];
+ Box::from_raw(ptr);
+ }
+ }
+}
+
+/// Receiver handle to a channel.
+pub struct Receiver<'a, T>(&'a Channel<T>);
+
+/// Sender handle to a channel.
+pub struct Sender<'a, T>(&'a Channel<T>);
+
+impl<T> SelectHandle for Receiver<'_, T> {
+ fn try_select(&self, token: &mut Token) -> bool {
+ self.0.start_recv(token)
+ }
+
+ fn deadline(&self) -> Option<Instant> {
+ None
+ }
+
+ fn register(&self, oper: Operation, cx: &Context) -> bool {
+ self.0.receivers.register(oper, cx);
+ self.is_ready()
+ }
+
+ fn unregister(&self, oper: Operation) {
+ self.0.receivers.unregister(oper);
+ }
+
+ fn accept(&self, token: &mut Token, _cx: &Context) -> bool {
+ self.try_select(token)
+ }
+
+ fn is_ready(&self) -> bool {
+ !self.0.is_empty() || self.0.is_disconnected()
+ }
+
+ fn watch(&self, oper: Operation, cx: &Context) -> bool {
+ self.0.receivers.watch(oper, cx);
+ self.is_ready()
+ }
+
+ fn unwatch(&self, oper: Operation) {
+ self.0.receivers.unwatch(oper);
+ }
+}
+
+impl<T> SelectHandle for Sender<'_, T> {
+ fn try_select(&self, token: &mut Token) -> bool {
+ self.0.start_send(token)
+ }
+
+ fn deadline(&self) -> Option<Instant> {
+ None
+ }
+
+ fn register(&self, oper: Operation, cx: &Context) -> bool {
+ self.0.senders.register(oper, cx);
+ self.is_ready()
+ }
+
+ fn unregister(&self, oper: Operation) {
+ self.0.senders.unregister(oper);
+ }
+
+ fn accept(&self, token: &mut Token, _cx: &Context) -> bool {
+ self.try_select(token)
+ }
+
+ fn is_ready(&self) -> bool {
+ !self.0.is_full() || self.0.is_disconnected()
+ }
+
+ fn watch(&self, oper: Operation, cx: &Context) -> bool {
+ self.0.senders.watch(oper, cx);
+ self.is_ready()
+ }
+
+ fn unwatch(&self, oper: Operation) {
+ self.0.senders.unwatch(oper);
+ }
+}
diff --git a/src/flavors/at.rs b/src/flavors/at.rs
new file mode 100644
index 0000000..a2b1b57
--- /dev/null
+++ b/src/flavors/at.rs
@@ -0,0 +1,202 @@
+//! Channel that delivers a message at a certain moment in time.
+//!
+//! Messages cannot be sent into this kind of channel; they are materialized on demand.
+
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::thread;
+use std::time::{Duration, Instant};
+
+use crate::context::Context;
+use crate::err::{RecvTimeoutError, TryRecvError};
+use crate::select::{Operation, SelectHandle, Token};
+use crate::utils;
+
+/// Result of a receive operation.
+pub type AtToken = Option<Instant>;
+
+/// Channel that delivers a message at a certain moment in time
+pub struct Channel {
+ /// The instant at which the message will be delivered.
+ delivery_time: Instant,
+
+ /// `true` if the message has been received.
+ received: AtomicBool,
+}
+
+impl Channel {
+ /// Creates a channel that delivers a message at a certain instant in time.
+ #[inline]
+ pub fn new_deadline(when: Instant) -> Self {
+ Channel {
+ delivery_time: when,
+ received: AtomicBool::new(false),
+ }
+ }
+ /// Creates a channel that delivers a message after a certain duration of time.
+ #[inline]
+ pub fn new_timeout(dur: Duration) -> Self {
+ Self::new_deadline(Instant::now() + dur)
+ }
+
+ /// Attempts to receive a message without blocking.
+ #[inline]
+ pub fn try_recv(&self) -> Result<Instant, TryRecvError> {
+ // We use relaxed ordering because this is just an optional optimistic check.
+ if self.received.load(Ordering::Relaxed) {
+ // The message has already been received.
+ return Err(TryRecvError::Empty);
+ }
+
+ if Instant::now() < self.delivery_time {
+ // The message was not delivered yet.
+ return Err(TryRecvError::Empty);
+ }
+
+ // Try receiving the message if it is still available.
+ if !self.received.swap(true, Ordering::SeqCst) {
+ // Success! Return delivery time as the message.
+ Ok(self.delivery_time)
+ } else {
+ // The message was already received.
+ Err(TryRecvError::Empty)
+ }
+ }
+
+ /// Receives a message from the channel.
+ #[inline]
+ pub fn recv(&self, deadline: Option<Instant>) -> Result<Instant, RecvTimeoutError> {
+ // We use relaxed ordering because this is just an optional optimistic check.
+ if self.received.load(Ordering::Relaxed) {
+ // The message has already been received.
+ utils::sleep_until(deadline);
+ return Err(RecvTimeoutError::Timeout);
+ }
+
+ // Wait until the message is received or the deadline is reached.
+ loop {
+ let now = Instant::now();
+
+ let deadline = match deadline {
+ // Check if we can receive the next message.
+ _ if now >= self.delivery_time => break,
+ // Check if the timeout deadline has been reached.
+ Some(d) if now >= d => return Err(RecvTimeoutError::Timeout),
+
+ // Sleep until one of the above happens
+ Some(d) if d < self.delivery_time => d,
+ _ => self.delivery_time,
+ };
+
+ thread::sleep(deadline - now);
+ }
+
+ // Try receiving the message if it is still available.
+ if !self.received.swap(true, Ordering::SeqCst) {
+ // Success! Return the message, which is the instant at which it was delivered.
+ Ok(self.delivery_time)
+ } else {
+ // The message was already received. Block forever.
+ utils::sleep_until(None);
+ unreachable!()
+ }
+ }
+
+ /// Reads a message from the channel.
+ #[inline]
+ pub unsafe fn read(&self, token: &mut Token) -> Result<Instant, ()> {
+ token.at.ok_or(())
+ }
+
+ /// Returns `true` if the channel is empty.
+ #[inline]
+ pub fn is_empty(&self) -> bool {
+ // We use relaxed ordering because this is just an optional optimistic check.
+ if self.received.load(Ordering::Relaxed) {
+ return true;
+ }
+
+ // If the delivery time hasn't been reached yet, the channel is empty.
+ if Instant::now() < self.delivery_time {
+ return true;
+ }
+
+ // The delivery time has been reached. The channel is empty only if the message has already
+ // been received.
+ self.received.load(Ordering::SeqCst)
+ }
+
+ /// Returns `true` if the channel is full.
+ #[inline]
+ pub fn is_full(&self) -> bool {
+ !self.is_empty()
+ }
+
+ /// Returns the number of messages in the channel.
+ #[inline]
+ pub fn len(&self) -> usize {
+ if self.is_empty() {
+ 0
+ } else {
+ 1
+ }
+ }
+
+ /// Returns the capacity of the channel.
+ #[inline]
+ pub fn capacity(&self) -> Option<usize> {
+ Some(1)
+ }
+}
+
+impl SelectHandle for Channel {
+ #[inline]
+ fn try_select(&self, token: &mut Token) -> bool {
+ match self.try_recv() {
+ Ok(msg) => {
+ token.at = Some(msg);
+ true
+ }
+ Err(TryRecvError::Disconnected) => {
+ token.at = None;
+ true
+ }
+ Err(TryRecvError::Empty) => false,
+ }
+ }
+
+ #[inline]
+ fn deadline(&self) -> Option<Instant> {
+ // We use relaxed ordering because this is just an optional optimistic check.
+ if self.received.load(Ordering::Relaxed) {
+ None
+ } else {
+ Some(self.delivery_time)
+ }
+ }
+
+ #[inline]
+ fn register(&self, _oper: Operation, _cx: &Context) -> bool {
+ self.is_ready()
+ }
+
+ #[inline]
+ fn unregister(&self, _oper: Operation) {}
+
+ #[inline]
+ fn accept(&self, token: &mut Token, _cx: &Context) -> bool {
+ self.try_select(token)
+ }
+
+ #[inline]
+ fn is_ready(&self) -> bool {
+ !self.is_empty()
+ }
+
+ #[inline]
+ fn watch(&self, _oper: Operation, _cx: &Context) -> bool {
+ self.is_ready()
+ }
+
+ #[inline]
+ fn unwatch(&self, _oper: Operation) {}
+}
diff --git a/src/flavors/list.rs b/src/flavors/list.rs
new file mode 100644
index 0000000..532e8b6
--- /dev/null
+++ b/src/flavors/list.rs
@@ -0,0 +1,669 @@
+//! Unbounded channel implemented as a linked list.
+
+use std::cell::UnsafeCell;
+use std::marker::PhantomData;
+use std::mem::MaybeUninit;
+use std::ptr;
+use std::sync::atomic::{self, AtomicPtr, AtomicUsize, Ordering};
+use std::time::Instant;
+
+use crossbeam_utils::{Backoff, CachePadded};
+
+use crate::context::Context;
+use crate::err::{RecvTimeoutError, SendTimeoutError, TryRecvError, TrySendError};
+use crate::select::{Operation, SelectHandle, Selected, Token};
+use crate::waker::SyncWaker;
+
+// TODO(stjepang): Once we bump the minimum required Rust version to 1.28 or newer, re-apply the
+// following changes by @kleimkuhler:
+//
+// 1. https://github.com/crossbeam-rs/crossbeam-channel/pull/100
+// 2. https://github.com/crossbeam-rs/crossbeam-channel/pull/101
+
+// Bits indicating the state of a slot:
+// * If a message has been written into the slot, `WRITE` is set.
+// * If a message has been read from the slot, `READ` is set.
+// * If the block is being destroyed, `DESTROY` is set.
+const WRITE: usize = 1;
+const READ: usize = 2;
+const DESTROY: usize = 4;
+
+// Each block covers one "lap" of indices.
+const LAP: usize = 32;
+// The maximum number of messages a block can hold.
+const BLOCK_CAP: usize = LAP - 1;
+// How many lower bits are reserved for metadata.
+const SHIFT: usize = 1;
+// Has two different purposes:
+// * If set in head, indicates that the block is not the last one.
+// * If set in tail, indicates that the channel is disconnected.
+const MARK_BIT: usize = 1;
+
+/// A slot in a block.
+struct Slot<T> {
+ /// The message.
+ msg: UnsafeCell<MaybeUninit<T>>,
+
+ /// The state of the slot.
+ state: AtomicUsize,
+}
+
+impl<T> Slot<T> {
+ /// Waits until a message is written into the slot.
+ fn wait_write(&self) {
+ let backoff = Backoff::new();
+ while self.state.load(Ordering::Acquire) & WRITE == 0 {
+ backoff.snooze();
+ }
+ }
+}
+
+/// A block in a linked list.
+///
+/// Each block in the list can hold up to `BLOCK_CAP` messages.
+struct Block<T> {
+ /// The next block in the linked list.
+ next: AtomicPtr<Block<T>>,
+
+ /// Slots for messages.
+ slots: [Slot<T>; BLOCK_CAP],
+}
+
+impl<T> Block<T> {
+ /// Creates an empty block.
+ fn new() -> Block<T> {
+ // SAFETY: This is safe because:
+ // [1] `Block::next` (AtomicPtr) may be safely zero initialized.
+ // [2] `Block::slots` (Array) may be safely zero initialized because of [3, 4].
+ // [3] `Slot::msg` (UnsafeCell) may be safely zero initialized because it
+ // holds a MaybeUninit.
+ // [4] `Slot::state` (AtomicUsize) may be safely zero initialized.
+ unsafe { MaybeUninit::zeroed().assume_init() }
+ }
+
+ /// Waits until the next pointer is set.
+ fn wait_next(&self) -> *mut Block<T> {
+ let backoff = Backoff::new();
+ loop {
+ let next = self.next.load(Ordering::Acquire);
+ if !next.is_null() {
+ return next;
+ }
+ backoff.snooze();
+ }
+ }
+
+ /// Sets the `DESTROY` bit in slots starting from `start` and destroys the block.
+ unsafe fn destroy(this: *mut Block<T>, start: usize) {
+ // It is not necessary to set the `DESTROY` bit in the last slot because that slot has
+ // begun destruction of the block.
+ for i in start..BLOCK_CAP - 1 {
+ let slot = (*this).slots.get_unchecked(i);
+
+ // Mark the `DESTROY` bit if a thread is still using the slot.
+ if slot.state.load(Ordering::Acquire) & READ == 0
+ && slot.state.fetch_or(DESTROY, Ordering::AcqRel) & READ == 0
+ {
+ // If a thread is still using the slot, it will continue destruction of the block.
+ return;
+ }
+ }
+
+ // No thread is using the block, now it is safe to destroy it.
+ drop(Box::from_raw(this));
+ }
+}
+
+/// A position in a channel.
+#[derive(Debug)]
+struct Position<T> {
+ /// The index in the channel.
+ index: AtomicUsize,
+
+ /// The block in the linked list.
+ block: AtomicPtr<Block<T>>,
+}
+
+/// The token type for the list flavor.
+#[derive(Debug)]
+pub struct ListToken {
+ /// The block of slots.
+ block: *const u8,
+
+ /// The offset into the block.
+ offset: usize,
+}
+
+impl Default for ListToken {
+ #[inline]
+ fn default() -> Self {
+ ListToken {
+ block: ptr::null(),
+ offset: 0,
+ }
+ }
+}
+
+/// Unbounded channel implemented as a linked list.
+///
+/// Each message sent into the channel is assigned a sequence number, i.e. an index. Indices are
+/// represented as numbers of type `usize` and wrap on overflow.
+///
+/// Consecutive messages are grouped into blocks in order to put less pressure on the allocator and
+/// improve cache efficiency.
+pub struct Channel<T> {
+ /// The head of the channel.
+ head: CachePadded<Position<T>>,
+
+ /// The tail of the channel.
+ tail: CachePadded<Position<T>>,
+
+ /// Receivers waiting while the channel is empty and not disconnected.
+ receivers: SyncWaker,
+
+ /// Indicates that dropping a `Channel<T>` may drop messages of type `T`.
+ _marker: PhantomData<T>,
+}
+
+impl<T> Channel<T> {
+ /// Creates a new unbounded channel.
+ pub fn new() -> Self {
+ Channel {
+ head: CachePadded::new(Position {
+ block: AtomicPtr::new(ptr::null_mut()),
+ index: AtomicUsize::new(0),
+ }),
+ tail: CachePadded::new(Position {
+ block: AtomicPtr::new(ptr::null_mut()),
+ index: AtomicUsize::new(0),
+ }),
+ receivers: SyncWaker::new(),
+ _marker: PhantomData,
+ }
+ }
+
+ /// Returns a receiver handle to the channel.
+ pub fn receiver(&self) -> Receiver<'_, T> {
+ Receiver(self)
+ }
+
+ /// Returns a sender handle to the channel.
+ pub fn sender(&self) -> Sender<'_, T> {
+ Sender(self)
+ }
+
+ /// Attempts to reserve a slot for sending a message.
+ fn start_send(&self, token: &mut Token) -> bool {
+ let backoff = Backoff::new();
+ let mut tail = self.tail.index.load(Ordering::Acquire);
+ let mut block = self.tail.block.load(Ordering::Acquire);
+ let mut next_block = None;
+
+ loop {
+ // Check if the channel is disconnected.
+ if tail & MARK_BIT != 0 {
+ token.list.block = ptr::null();
+ return true;
+ }
+
+ // Calculate the offset of the index into the block.
+ let offset = (tail >> SHIFT) % LAP;
+
+ // If we reached the end of the block, wait until the next one is installed.
+ if offset == BLOCK_CAP {
+ backoff.snooze();
+ tail = self.tail.index.load(Ordering::Acquire);
+ block = self.tail.block.load(Ordering::Acquire);
+ continue;
+ }
+
+ // If we're going to have to install the next block, allocate it in advance in order to
+ // make the wait for other threads as short as possible.
+ if offset + 1 == BLOCK_CAP && next_block.is_none() {
+ next_block = Some(Box::new(Block::<T>::new()));
+ }
+
+ // If this is the first message to be sent into the channel, we need to allocate the
+ // first block and install it.
+ if block.is_null() {
+ let new = Box::into_raw(Box::new(Block::<T>::new()));
+
+ if self
+ .tail
+ .block
+ .compare_and_swap(block, new, Ordering::Release)
+ == block
+ {
+ self.head.block.store(new, Ordering::Release);
+ block = new;
+ } else {
+ next_block = unsafe { Some(Box::from_raw(new)) };
+ tail = self.tail.index.load(Ordering::Acquire);
+ block = self.tail.block.load(Ordering::Acquire);
+ continue;
+ }
+ }
+
+ let new_tail = tail + (1 << SHIFT);
+
+ // Try advancing the tail forward.
+ match self.tail.index.compare_exchange_weak(
+ tail,
+ new_tail,
+ Ordering::SeqCst,
+ Ordering::Acquire,
+ ) {
+ Ok(_) => unsafe {
+ // If we've reached the end of the block, install the next one.
+ if offset + 1 == BLOCK_CAP {
+ let next_block = Box::into_raw(next_block.unwrap());
+ self.tail.block.store(next_block, Ordering::Release);
+ self.tail.index.fetch_add(1 << SHIFT, Ordering::Release);
+ (*block).next.store(next_block, Ordering::Release);
+ }
+
+ token.list.block = block as *const u8;
+ token.list.offset = offset;
+ return true;
+ },
+ Err(t) => {
+ tail = t;
+ block = self.tail.block.load(Ordering::Acquire);
+ backoff.spin();
+ }
+ }
+ }
+ }
+
+ /// Writes a message into the channel.
+ pub unsafe fn write(&self, token: &mut Token, msg: T) -> Result<(), T> {
+ // If there is no slot, the channel is disconnected.
+ if token.list.block.is_null() {
+ return Err(msg);
+ }
+
+ // Write the message into the slot.
+ let block = token.list.block as *mut Block<T>;
+ let offset = token.list.offset;
+ let slot = (*block).slots.get_unchecked(offset);
+ slot.msg.get().write(MaybeUninit::new(msg));
+ slot.state.fetch_or(WRITE, Ordering::Release);
+
+ // Wake a sleeping receiver.
+ self.receivers.notify();
+ Ok(())
+ }
+
+ /// Attempts to reserve a slot for receiving a message.
+ fn start_recv(&self, token: &mut Token) -> bool {
+ let backoff = Backoff::new();
+ let mut head = self.head.index.load(Ordering::Acquire);
+ let mut block = self.head.block.load(Ordering::Acquire);
+
+ loop {
+ // Calculate the offset of the index into the block.
+ let offset = (head >> SHIFT) % LAP;
+
+ // If we reached the end of the block, wait until the next one is installed.
+ if offset == BLOCK_CAP {
+ backoff.snooze();
+ head = self.head.index.load(Ordering::Acquire);
+ block = self.head.block.load(Ordering::Acquire);
+ continue;
+ }
+
+ let mut new_head = head + (1 << SHIFT);
+
+ if new_head & MARK_BIT == 0 {
+ atomic::fence(Ordering::SeqCst);
+ let tail = self.tail.index.load(Ordering::Relaxed);
+
+ // If the tail equals the head, that means the channel is empty.
+ if head >> SHIFT == tail >> SHIFT {
+ // If the channel is disconnected...
+ if tail & MARK_BIT != 0 {
+ // ...then receive an error.
+ token.list.block = ptr::null();
+ return true;
+ } else {
+ // Otherwise, the receive operation is not ready.
+ return false;
+ }
+ }
+
+ // If head and tail are not in the same block, set `MARK_BIT` in head.
+ if (head >> SHIFT) / LAP != (tail >> SHIFT) / LAP {
+ new_head |= MARK_BIT;
+ }
+ }
+
+ // The block can be null here only if the first message is being sent into the channel.
+ // In that case, just wait until it gets initialized.
+ if block.is_null() {
+ backoff.snooze();
+ head = self.head.index.load(Ordering::Acquire);
+ block = self.head.block.load(Ordering::Acquire);
+ continue;
+ }
+
+ // Try moving the head index forward.
+ match self.head.index.compare_exchange_weak(
+ head,
+ new_head,
+ Ordering::SeqCst,
+ Ordering::Acquire,
+ ) {
+ Ok(_) => unsafe {
+ // If we've reached the end of the block, move to the next one.
+ if offset + 1 == BLOCK_CAP {
+ let next = (*block).wait_next();
+ let mut next_index = (new_head & !MARK_BIT).wrapping_add(1 << SHIFT);
+ if !(*next).next.load(Ordering::Relaxed).is_null() {
+ next_index |= MARK_BIT;
+ }
+
+ self.head.block.store(next, Ordering::Release);
+ self.head.index.store(next_index, Ordering::Release);
+ }
+
+ token.list.block = block as *const u8;
+ token.list.offset = offset;
+ return true;
+ },
+ Err(h) => {
+ head = h;
+ block = self.head.block.load(Ordering::Acquire);
+ backoff.spin();
+ }
+ }
+ }
+ }
+
+ /// Reads a message from the channel.
+ pub unsafe fn read(&self, token: &mut Token) -> Result<T, ()> {
+ if token.list.block.is_null() {
+ // The channel is disconnected.
+ return Err(());
+ }
+
+ // Read the message.
+ let block = token.list.block as *mut Block<T>;
+ let offset = token.list.offset;
+ let slot = (*block).slots.get_unchecked(offset);
+ slot.wait_write();
+ let msg = slot.msg.get().read().assume_init();
+
+ // Destroy the block if we've reached the end, or if another thread wanted to destroy but
+ // couldn't because we were busy reading from the slot.
+ if offset + 1 == BLOCK_CAP {
+ Block::destroy(block, 0);
+ } else if slot.state.fetch_or(READ, Ordering::AcqRel) & DESTROY != 0 {
+ Block::destroy(block, offset + 1);
+ }
+
+ Ok(msg)
+ }
+
+ /// Attempts to send a message into the channel.
+ pub fn try_send(&self, msg: T) -> Result<(), TrySendError<T>> {
+ self.send(msg, None).map_err(|err| match err {
+ SendTimeoutError::Disconnected(msg) => TrySendError::Disconnected(msg),
+ SendTimeoutError::Timeout(_) => unreachable!(),
+ })
+ }
+
+ /// Sends a message into the channel.
+ pub fn send(&self, msg: T, _deadline: Option<Instant>) -> Result<(), SendTimeoutError<T>> {
+ let token = &mut Token::default();
+ assert!(self.start_send(token));
+ unsafe {
+ self.write(token, msg)
+ .map_err(SendTimeoutError::Disconnected)
+ }
+ }
+
+ /// Attempts to receive a message without blocking.
+ pub fn try_recv(&self) -> Result<T, TryRecvError> {
+ let token = &mut Token::default();
+
+ if self.start_recv(token) {
+ unsafe { self.read(token).map_err(|_| TryRecvError::Disconnected) }
+ } else {
+ Err(TryRecvError::Empty)
+ }
+ }
+
+ /// Receives a message from the channel.
+ pub fn recv(&self, deadline: Option<Instant>) -> Result<T, RecvTimeoutError> {
+ let token = &mut Token::default();
+ loop {
+ // Try receiving a message several times.
+ let backoff = Backoff::new();
+ loop {
+ if self.start_recv(token) {
+ unsafe {
+ return self.read(token).map_err(|_| RecvTimeoutError::Disconnected);
+ }
+ }
+
+ if backoff.is_completed() {
+ break;
+ } else {
+ backoff.snooze();
+ }
+ }
+
+ if let Some(d) = deadline {
+ if Instant::now() >= d {
+ return Err(RecvTimeoutError::Timeout);
+ }
+ }
+
+ // Prepare for blocking until a sender wakes us up.
+ Context::with(|cx| {
+ let oper = Operation::hook(token);
+ self.receivers.register(oper, cx);
+
+ // Has the channel become ready just now?
+ if !self.is_empty() || self.is_disconnected() {
+ let _ = cx.try_select(Selected::Aborted);
+ }
+
+ // Block the current thread.
+ let sel = cx.wait_until(deadline);
+
+ match sel {
+ Selected::Waiting => unreachable!(),
+ Selected::Aborted | Selected::Disconnected => {
+ self.receivers.unregister(oper).unwrap();
+ // If the channel was disconnected, we still have to check for remaining
+ // messages.
+ }
+ Selected::Operation(_) => {}
+ }
+ });
+ }
+ }
+
+ /// Returns the current number of messages inside the channel.
+ pub fn len(&self) -> usize {
+ loop {
+ // Load the tail index, then load the head index.
+ let mut tail = self.tail.index.load(Ordering::SeqCst);
+ let mut head = self.head.index.load(Ordering::SeqCst);
+
+ // If the tail index didn't change, we've got consistent indices to work with.
+ if self.tail.index.load(Ordering::SeqCst) == tail {
+ // Erase the lower bits.
+ tail &= !((1 << SHIFT) - 1);
+ head &= !((1 << SHIFT) - 1);
+
+ // Fix up indices if they fall onto block ends.
+ if (tail >> SHIFT) & (LAP - 1) == LAP - 1 {
+ tail = tail.wrapping_add(1 << SHIFT);
+ }
+ if (head >> SHIFT) & (LAP - 1) == LAP - 1 {
+ head = head.wrapping_add(1 << SHIFT);
+ }
+
+ // Rotate indices so that head falls into the first block.
+ let lap = (head >> SHIFT) / LAP;
+ tail = tail.wrapping_sub((lap * LAP) << SHIFT);
+ head = head.wrapping_sub((lap * LAP) << SHIFT);
+
+ // Remove the lower bits.
+ tail >>= SHIFT;
+ head >>= SHIFT;
+
+ // Return the difference minus the number of blocks between tail and head.
+ return tail - head - tail / LAP;
+ }
+ }
+ }
+
+ /// Returns the capacity of the channel.
+ pub fn capacity(&self) -> Option<usize> {
+ None
+ }
+
+ /// Disconnects the channel and wakes up all blocked receivers.
+ ///
+ /// Returns `true` if this call disconnected the channel.
+ pub fn disconnect(&self) -> bool {
+ let tail = self.tail.index.fetch_or(MARK_BIT, Ordering::SeqCst);
+
+ if tail & MARK_BIT == 0 {
+ self.receivers.disconnect();
+ true
+ } else {
+ false
+ }
+ }
+
+ /// Returns `true` if the channel is disconnected.
+ pub fn is_disconnected(&self) -> bool {
+ self.tail.index.load(Ordering::SeqCst) & MARK_BIT != 0
+ }
+
+ /// Returns `true` if the channel is empty.
+ pub fn is_empty(&self) -> bool {
+ let head = self.head.index.load(Ordering::SeqCst);
+ let tail = self.tail.index.load(Ordering::SeqCst);
+ head >> SHIFT == tail >> SHIFT
+ }
+
+ /// Returns `true` if the channel is full.
+ pub fn is_full(&self) -> bool {
+ false
+ }
+}
+
+impl<T> Drop for Channel<T> {
+ fn drop(&mut self) {
+ let mut head = self.head.index.load(Ordering::Relaxed);
+ let mut tail = self.tail.index.load(Ordering::Relaxed);
+ let mut block = self.head.block.load(Ordering::Relaxed);
+
+ // Erase the lower bits.
+ head &= !((1 << SHIFT) - 1);
+ tail &= !((1 << SHIFT) - 1);
+
+ unsafe {
+ // Drop all messages between head and tail and deallocate the heap-allocated blocks.
+ while head != tail {
+ let offset = (head >> SHIFT) % LAP;
+
+ if offset < BLOCK_CAP {
+ // Drop the message in the slot.
+ let slot = (*block).slots.get_unchecked(offset);
+ let p = &mut *slot.msg.get();
+ p.as_mut_ptr().drop_in_place();
+ } else {
+ // Deallocate the block and move to the next one.
+ let next = (*block).next.load(Ordering::Relaxed);
+ drop(Box::from_raw(block));
+ block = next;
+ }
+
+ head = head.wrapping_add(1 << SHIFT);
+ }
+
+ // Deallocate the last remaining block.
+ if !block.is_null() {
+ drop(Box::from_raw(block));
+ }
+ }
+ }
+}
+
+/// Receiver handle to a channel.
+pub struct Receiver<'a, T>(&'a Channel<T>);
+
+/// Sender handle to a channel.
+pub struct Sender<'a, T>(&'a Channel<T>);
+
+impl<T> SelectHandle for Receiver<'_, T> {
+ fn try_select(&self, token: &mut Token) -> bool {
+ self.0.start_recv(token)
+ }
+
+ fn deadline(&self) -> Option<Instant> {
+ None
+ }
+
+ fn register(&self, oper: Operation, cx: &Context) -> bool {
+ self.0.receivers.register(oper, cx);
+ self.is_ready()
+ }
+
+ fn unregister(&self, oper: Operation) {
+ self.0.receivers.unregister(oper);
+ }
+
+ fn accept(&self, token: &mut Token, _cx: &Context) -> bool {
+ self.try_select(token)
+ }
+
+ fn is_ready(&self) -> bool {
+ !self.0.is_empty() || self.0.is_disconnected()
+ }
+
+ fn watch(&self, oper: Operation, cx: &Context) -> bool {
+ self.0.receivers.watch(oper, cx);
+ self.is_ready()
+ }
+
+ fn unwatch(&self, oper: Operation) {
+ self.0.receivers.unwatch(oper);
+ }
+}
+
+impl<T> SelectHandle for Sender<'_, T> {
+ fn try_select(&self, token: &mut Token) -> bool {
+ self.0.start_send(token)
+ }
+
+ fn deadline(&self) -> Option<Instant> {
+ None
+ }
+
+ fn register(&self, _oper: Operation, _cx: &Context) -> bool {
+ self.is_ready()
+ }
+
+ fn unregister(&self, _oper: Operation) {}
+
+ fn accept(&self, token: &mut Token, _cx: &Context) -> bool {
+ self.try_select(token)
+ }
+
+ fn is_ready(&self) -> bool {
+ true
+ }
+
+ fn watch(&self, _oper: Operation, _cx: &Context) -> bool {
+ self.is_ready()
+ }
+
+ fn unwatch(&self, _oper: Operation) {}
+}
diff --git a/src/flavors/mod.rs b/src/flavors/mod.rs
new file mode 100644
index 0000000..299e78f
--- /dev/null
+++ b/src/flavors/mod.rs
@@ -0,0 +1,17 @@
+//! Channel flavors.
+//!
+//! There are six flavors:
+//!
+//! 1. `at` - Channel that delivers a message after a certain amount of time.
+//! 2. `array` - Bounded channel based on a preallocated array.
+//! 3. `list` - Unbounded channel implemented as a linked list.
+//! 4. `never` - Channel that never delivers messages.
+//! 5. `tick` - Channel that delivers messages periodically.
+//! 6. `zero` - Zero-capacity channel.
+
+pub mod array;
+pub mod at;
+pub mod list;
+pub mod never;
+pub mod tick;
+pub mod zero;
diff --git a/src/flavors/never.rs b/src/flavors/never.rs
new file mode 100644
index 0000000..e49d214
--- /dev/null
+++ b/src/flavors/never.rs
@@ -0,0 +1,110 @@
+//! Channel that never delivers messages.
+//!
+//! Messages cannot be sent into this kind of channel.
+
+use std::marker::PhantomData;
+use std::time::Instant;
+
+use crate::context::Context;
+use crate::err::{RecvTimeoutError, TryRecvError};
+use crate::select::{Operation, SelectHandle, Token};
+use crate::utils;
+
+/// This flavor doesn't need a token.
+pub type NeverToken = ();
+
+/// Channel that never delivers messages.
+pub struct Channel<T> {
+ _marker: PhantomData<T>,
+}
+
+impl<T> Channel<T> {
+ /// Creates a channel that never delivers messages.
+ #[inline]
+ pub fn new() -> Self {
+ Channel {
+ _marker: PhantomData,
+ }
+ }
+
+ /// Attempts to receive a message without blocking.
+ #[inline]
+ pub fn try_recv(&self) -> Result<T, TryRecvError> {
+ Err(TryRecvError::Empty)
+ }
+
+ /// Receives a message from the channel.
+ #[inline]
+ pub fn recv(&self, deadline: Option<Instant>) -> Result<T, RecvTimeoutError> {
+ utils::sleep_until(deadline);
+ Err(RecvTimeoutError::Timeout)
+ }
+
+ /// Reads a message from the channel.
+ #[inline]
+ pub unsafe fn read(&self, _token: &mut Token) -> Result<T, ()> {
+ Err(())
+ }
+
+ /// Returns `true` if the channel is empty.
+ #[inline]
+ pub fn is_empty(&self) -> bool {
+ true
+ }
+
+ /// Returns `true` if the channel is full.
+ #[inline]
+ pub fn is_full(&self) -> bool {
+ true
+ }
+
+ /// Returns the number of messages in the channel.
+ #[inline]
+ pub fn len(&self) -> usize {
+ 0
+ }
+
+ /// Returns the capacity of the channel.
+ #[inline]
+ pub fn capacity(&self) -> Option<usize> {
+ Some(0)
+ }
+}
+
+impl<T> SelectHandle for Channel<T> {
+ #[inline]
+ fn try_select(&self, _token: &mut Token) -> bool {
+ false
+ }
+
+ #[inline]
+ fn deadline(&self) -> Option<Instant> {
+ None
+ }
+
+ #[inline]
+ fn register(&self, _oper: Operation, _cx: &Context) -> bool {
+ self.is_ready()
+ }
+
+ #[inline]
+ fn unregister(&self, _oper: Operation) {}
+
+ #[inline]
+ fn accept(&self, token: &mut Token, _cx: &Context) -> bool {
+ self.try_select(token)
+ }
+
+ #[inline]
+ fn is_ready(&self) -> bool {
+ false
+ }
+
+ #[inline]
+ fn watch(&self, _oper: Operation, _cx: &Context) -> bool {
+ self.is_ready()
+ }
+
+ #[inline]
+ fn unwatch(&self, _oper: Operation) {}
+}
diff --git a/src/flavors/tick.rs b/src/flavors/tick.rs
new file mode 100644
index 0000000..e8e7020
--- /dev/null
+++ b/src/flavors/tick.rs
@@ -0,0 +1,167 @@
+//! Channel that delivers messages periodically.
+//!
+//! Messages cannot be sent into this kind of channel; they are materialized on demand.
+
+use std::thread;
+use std::time::{Duration, Instant};
+
+use crossbeam_utils::atomic::AtomicCell;
+
+use crate::context::Context;
+use crate::err::{RecvTimeoutError, TryRecvError};
+use crate::select::{Operation, SelectHandle, Token};
+
+/// Result of a receive operation.
+pub type TickToken = Option<Instant>;
+
+/// Channel that delivers messages periodically.
+pub struct Channel {
+ /// The instant at which the next message will be delivered.
+ delivery_time: AtomicCell<Instant>,
+
+ /// The time interval in which messages get delivered.
+ duration: Duration,
+}
+
+impl Channel {
+ /// Creates a channel that delivers messages periodically.
+ #[inline]
+ pub fn new(dur: Duration) -> Self {
+ Channel {
+ delivery_time: AtomicCell::new(Instant::now() + dur),
+ duration: dur,
+ }
+ }
+
+ /// Attempts to receive a message without blocking.
+ #[inline]
+ pub fn try_recv(&self) -> Result<Instant, TryRecvError> {
+ loop {
+ let now = Instant::now();
+ let delivery_time = self.delivery_time.load();
+
+ if now < delivery_time {
+ return Err(TryRecvError::Empty);
+ }
+
+ if self
+ .delivery_time
+ .compare_exchange(delivery_time, now + self.duration)
+ .is_ok()
+ {
+ return Ok(delivery_time);
+ }
+ }
+ }
+
+ /// Receives a message from the channel.
+ #[inline]
+ pub fn recv(&self, deadline: Option<Instant>) -> Result<Instant, RecvTimeoutError> {
+ loop {
+ let delivery_time = self.delivery_time.load();
+ let now = Instant::now();
+
+ if let Some(d) = deadline {
+ if d < delivery_time {
+ if now < d {
+ thread::sleep(d - now);
+ }
+ return Err(RecvTimeoutError::Timeout);
+ }
+ }
+
+ if self
+ .delivery_time
+ .compare_exchange(delivery_time, delivery_time.max(now) + self.duration)
+ .is_ok()
+ {
+ if now < delivery_time {
+ thread::sleep(delivery_time - now);
+ }
+ return Ok(delivery_time);
+ }
+ }
+ }
+
+ /// Reads a message from the channel.
+ #[inline]
+ pub unsafe fn read(&self, token: &mut Token) -> Result<Instant, ()> {
+ token.tick.ok_or(())
+ }
+
+ /// Returns `true` if the channel is empty.
+ #[inline]
+ pub fn is_empty(&self) -> bool {
+ Instant::now() < self.delivery_time.load()
+ }
+
+ /// Returns `true` if the channel is full.
+ #[inline]
+ pub fn is_full(&self) -> bool {
+ !self.is_empty()
+ }
+
+ /// Returns the number of messages in the channel.
+ #[inline]
+ pub fn len(&self) -> usize {
+ if self.is_empty() {
+ 0
+ } else {
+ 1
+ }
+ }
+
+ /// Returns the capacity of the channel.
+ #[inline]
+ pub fn capacity(&self) -> Option<usize> {
+ Some(1)
+ }
+}
+
+impl SelectHandle for Channel {
+ #[inline]
+ fn try_select(&self, token: &mut Token) -> bool {
+ match self.try_recv() {
+ Ok(msg) => {
+ token.tick = Some(msg);
+ true
+ }
+ Err(TryRecvError::Disconnected) => {
+ token.tick = None;
+ true
+ }
+ Err(TryRecvError::Empty) => false,
+ }
+ }
+
+ #[inline]
+ fn deadline(&self) -> Option<Instant> {
+ Some(self.delivery_time.load())
+ }
+
+ #[inline]
+ fn register(&self, _oper: Operation, _cx: &Context) -> bool {
+ self.is_ready()
+ }
+
+ #[inline]
+ fn unregister(&self, _oper: Operation) {}
+
+ #[inline]
+ fn accept(&self, token: &mut Token, _cx: &Context) -> bool {
+ self.try_select(token)
+ }
+
+ #[inline]
+ fn is_ready(&self) -> bool {
+ !self.is_empty()
+ }
+
+ #[inline]
+ fn watch(&self, _oper: Operation, _cx: &Context) -> bool {
+ self.is_ready()
+ }
+
+ #[inline]
+ fn unwatch(&self, _oper: Operation) {}
+}
diff --git a/src/flavors/zero.rs b/src/flavors/zero.rs
new file mode 100644
index 0000000..be647b5
--- /dev/null
+++ b/src/flavors/zero.rs
@@ -0,0 +1,466 @@
+//! Zero-capacity channel.
+//!
+//! This kind of channel is also known as *rendezvous* channel.
+
+use std::cell::UnsafeCell;
+use std::marker::PhantomData;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::time::Instant;
+
+use crossbeam_utils::Backoff;
+
+use crate::context::Context;
+use crate::err::{RecvTimeoutError, SendTimeoutError, TryRecvError, TrySendError};
+use crate::select::{Operation, SelectHandle, Selected, Token};
+use crate::utils::Spinlock;
+use crate::waker::Waker;
+
+/// A pointer to a packet.
+pub type ZeroToken = usize;
+
+/// A slot for passing one message from a sender to a receiver.
+struct Packet<T> {
+ /// Equals `true` if the packet is allocated on the stack.
+ on_stack: bool,
+
+ /// Equals `true` once the packet is ready for reading or writing.
+ ready: AtomicBool,
+
+ /// The message.
+ msg: UnsafeCell<Option<T>>,
+}
+
+impl<T> Packet<T> {
+ /// Creates an empty packet on the stack.
+ fn empty_on_stack() -> Packet<T> {
+ Packet {
+ on_stack: true,
+ ready: AtomicBool::new(false),
+ msg: UnsafeCell::new(None),
+ }
+ }
+
+ /// Creates an empty packet on the heap.
+ fn empty_on_heap() -> Box<Packet<T>> {
+ Box::new(Packet {
+ on_stack: false,
+ ready: AtomicBool::new(false),
+ msg: UnsafeCell::new(None),
+ })
+ }
+
+ /// Creates a packet on the stack, containing a message.
+ fn message_on_stack(msg: T) -> Packet<T> {
+ Packet {
+ on_stack: true,
+ ready: AtomicBool::new(false),
+ msg: UnsafeCell::new(Some(msg)),
+ }
+ }
+
+ /// Waits until the packet becomes ready for reading or writing.
+ fn wait_ready(&self) {
+ let backoff = Backoff::new();
+ while !self.ready.load(Ordering::Acquire) {
+ backoff.snooze();
+ }
+ }
+}
+
+/// Inner representation of a zero-capacity channel.
+struct Inner {
+ /// Senders waiting to pair up with a receive operation.
+ senders: Waker,
+
+ /// Receivers waiting to pair up with a send operation.
+ receivers: Waker,
+
+ /// Equals `true` when the channel is disconnected.
+ is_disconnected: bool,
+}
+
+/// Zero-capacity channel.
+pub struct Channel<T> {
+ /// Inner representation of the channel.
+ inner: Spinlock<Inner>,
+
+ /// Indicates that dropping a `Channel<T>` may drop values of type `T`.
+ _marker: PhantomData<T>,
+}
+
+impl<T> Channel<T> {
+ /// Constructs a new zero-capacity channel.
+ pub fn new() -> Self {
+ Channel {
+ inner: Spinlock::new(Inner {
+ senders: Waker::new(),
+ receivers: Waker::new(),
+ is_disconnected: false,
+ }),
+ _marker: PhantomData,
+ }
+ }
+
+ /// Returns a receiver handle to the channel.
+ pub fn receiver(&self) -> Receiver<'_, T> {
+ Receiver(self)
+ }
+
+ /// Returns a sender handle to the channel.
+ pub fn sender(&self) -> Sender<'_, T> {
+ Sender(self)
+ }
+
+ /// Attempts to reserve a slot for sending a message.
+ fn start_send(&self, token: &mut Token) -> bool {
+ let mut inner = self.inner.lock();
+
+ // If there's a waiting receiver, pair up with it.
+ if let Some(operation) = inner.receivers.try_select() {
+ token.zero = operation.packet;
+ true
+ } else if inner.is_disconnected {
+ token.zero = 0;
+ true
+ } else {
+ false
+ }
+ }
+
+ /// Writes a message into the packet.
+ pub unsafe fn write(&self, token: &mut Token, msg: T) -> Result<(), T> {
+ // If there is no packet, the channel is disconnected.
+ if token.zero == 0 {
+ return Err(msg);
+ }
+
+ let packet = &*(token.zero as *const Packet<T>);
+ packet.msg.get().write(Some(msg));
+ packet.ready.store(true, Ordering::Release);
+ Ok(())
+ }
+
+ /// Attempts to pair up with a sender.
+ fn start_recv(&self, token: &mut Token) -> bool {
+ let mut inner = self.inner.lock();
+
+ // If there's a waiting sender, pair up with it.
+ if let Some(operation) = inner.senders.try_select() {
+ token.zero = operation.packet;
+ true
+ } else if inner.is_disconnected {
+ token.zero = 0;
+ true
+ } else {
+ false
+ }
+ }
+
+ /// Reads a message from the packet.
+ pub unsafe fn read(&self, token: &mut Token) -> Result<T, ()> {
+ // If there is no packet, the channel is disconnected.
+ if token.zero == 0 {
+ return Err(());
+ }
+
+ let packet = &*(token.zero as *const Packet<T>);
+
+ if packet.on_stack {
+ // The message has been in the packet from the beginning, so there is no need to wait
+ // for it. However, after reading the message, we need to set `ready` to `true` in
+ // order to signal that the packet can be destroyed.
+ let msg = packet.msg.get().replace(None).unwrap();
+ packet.ready.store(true, Ordering::Release);
+ Ok(msg)
+ } else {
+ // Wait until the message becomes available, then read it and destroy the
+ // heap-allocated packet.
+ packet.wait_ready();
+ let msg = packet.msg.get().replace(None).unwrap();
+ drop(Box::from_raw(packet as *const Packet<T> as *mut Packet<T>));
+ Ok(msg)
+ }
+ }
+
+ /// Attempts to send a message into the channel.
+ pub fn try_send(&self, msg: T) -> Result<(), TrySendError<T>> {
+ let token = &mut Token::default();
+ let mut inner = self.inner.lock();
+
+ // If there's a waiting receiver, pair up with it.
+ if let Some(operation) = inner.receivers.try_select() {
+ token.zero = operation.packet;
+ drop(inner);
+ unsafe {
+ self.write(token, msg).ok().unwrap();
+ }
+ Ok(())
+ } else if inner.is_disconnected {
+ Err(TrySendError::Disconnected(msg))
+ } else {
+ Err(TrySendError::Full(msg))
+ }
+ }
+
+ /// Sends a message into the channel.
+ pub fn send(&self, msg: T, deadline: Option<Instant>) -> Result<(), SendTimeoutError<T>> {
+ let token = &mut Token::default();
+ let mut inner = self.inner.lock();
+
+ // If there's a waiting receiver, pair up with it.
+ if let Some(operation) = inner.receivers.try_select() {
+ token.zero = operation.packet;
+ drop(inner);
+ unsafe {
+ self.write(token, msg).ok().unwrap();
+ }
+ return Ok(());
+ }
+
+ if inner.is_disconnected {
+ return Err(SendTimeoutError::Disconnected(msg));
+ }
+
+ Context::with(|cx| {
+ // Prepare for blocking until a receiver wakes us up.
+ let oper = Operation::hook(token);
+ let packet = Packet::<T>::message_on_stack(msg);
+ inner
+ .senders
+ .register_with_packet(oper, &packet as *const Packet<T> as usize, cx);
+ inner.receivers.notify();
+ drop(inner);
+
+ // Block the current thread.
+ let sel = cx.wait_until(deadline);
+
+ match sel {
+ Selected::Waiting => unreachable!(),
+ Selected::Aborted => {
+ self.inner.lock().senders.unregister(oper).unwrap();
+ let msg = unsafe { packet.msg.get().replace(None).unwrap() };
+ Err(SendTimeoutError::Timeout(msg))
+ }
+ Selected::Disconnected => {
+ self.inner.lock().senders.unregister(oper).unwrap();
+ let msg = unsafe { packet.msg.get().replace(None).unwrap() };
+ Err(SendTimeoutError::Disconnected(msg))
+ }
+ Selected::Operation(_) => {
+ // Wait until the message is read, then drop the packet.
+ packet.wait_ready();
+ Ok(())
+ }
+ }
+ })
+ }
+
+ /// Attempts to receive a message without blocking.
+ pub fn try_recv(&self) -> Result<T, TryRecvError> {
+ let token = &mut Token::default();
+ let mut inner = self.inner.lock();
+
+ // If there's a waiting sender, pair up with it.
+ if let Some(operation) = inner.senders.try_select() {
+ token.zero = operation.packet;
+ drop(inner);
+ unsafe { self.read(token).map_err(|_| TryRecvError::Disconnected) }
+ } else if inner.is_disconnected {
+ Err(TryRecvError::Disconnected)
+ } else {
+ Err(TryRecvError::Empty)
+ }
+ }
+
+ /// Receives a message from the channel.
+ pub fn recv(&self, deadline: Option<Instant>) -> Result<T, RecvTimeoutError> {
+ let token = &mut Token::default();
+ let mut inner = self.inner.lock();
+
+ // If there's a waiting sender, pair up with it.
+ if let Some(operation) = inner.senders.try_select() {
+ token.zero = operation.packet;
+ drop(inner);
+ unsafe {
+ return self.read(token).map_err(|_| RecvTimeoutError::Disconnected);
+ }
+ }
+
+ if inner.is_disconnected {
+ return Err(RecvTimeoutError::Disconnected);
+ }
+
+ Context::with(|cx| {
+ // Prepare for blocking until a sender wakes us up.
+ let oper = Operation::hook(token);
+ let packet = Packet::<T>::empty_on_stack();
+ inner
+ .receivers
+ .register_with_packet(oper, &packet as *const Packet<T> as usize, cx);
+ inner.senders.notify();
+ drop(inner);
+
+ // Block the current thread.
+ let sel = cx.wait_until(deadline);
+
+ match sel {
+ Selected::Waiting => unreachable!(),
+ Selected::Aborted => {
+ self.inner.lock().receivers.unregister(oper).unwrap();
+ Err(RecvTimeoutError::Timeout)
+ }
+ Selected::Disconnected => {
+ self.inner.lock().receivers.unregister(oper).unwrap();
+ Err(RecvTimeoutError::Disconnected)
+ }
+ Selected::Operation(_) => {
+ // Wait until the message is provided, then read it.
+ packet.wait_ready();
+ unsafe { Ok(packet.msg.get().replace(None).unwrap()) }
+ }
+ }
+ })
+ }
+
+ /// Disconnects the channel and wakes up all blocked senders and receivers.
+ ///
+ /// Returns `true` if this call disconnected the channel.
+ pub fn disconnect(&self) -> bool {
+ let mut inner = self.inner.lock();
+
+ if !inner.is_disconnected {
+ inner.is_disconnected = true;
+ inner.senders.disconnect();
+ inner.receivers.disconnect();
+ true
+ } else {
+ false
+ }
+ }
+
+ /// Returns the current number of messages inside the channel.
+ pub fn len(&self) -> usize {
+ 0
+ }
+
+ /// Returns the capacity of the channel.
+ pub fn capacity(&self) -> Option<usize> {
+ Some(0)
+ }
+
+ /// Returns `true` if the channel is empty.
+ pub fn is_empty(&self) -> bool {
+ true
+ }
+
+ /// Returns `true` if the channel is full.
+ pub fn is_full(&self) -> bool {
+ true
+ }
+}
+
+/// Receiver handle to a channel.
+pub struct Receiver<'a, T>(&'a Channel<T>);
+
+/// Sender handle to a channel.
+pub struct Sender<'a, T>(&'a Channel<T>);
+
+impl<T> SelectHandle for Receiver<'_, T> {
+ fn try_select(&self, token: &mut Token) -> bool {
+ self.0.start_recv(token)
+ }
+
+ fn deadline(&self) -> Option<Instant> {
+ None
+ }
+
+ fn register(&self, oper: Operation, cx: &Context) -> bool {
+ let packet = Box::into_raw(Packet::<T>::empty_on_heap());
+
+ let mut inner = self.0.inner.lock();
+ inner
+ .receivers
+ .register_with_packet(oper, packet as usize, cx);
+ inner.senders.notify();
+ inner.senders.can_select() || inner.is_disconnected
+ }
+
+ fn unregister(&self, oper: Operation) {
+ if let Some(operation) = self.0.inner.lock().receivers.unregister(oper) {
+ unsafe {
+ drop(Box::from_raw(operation.packet as *mut Packet<T>));
+ }
+ }
+ }
+
+ fn accept(&self, token: &mut Token, cx: &Context) -> bool {
+ token.zero = cx.wait_packet();
+ true
+ }
+
+ fn is_ready(&self) -> bool {
+ let inner = self.0.inner.lock();
+ inner.senders.can_select() || inner.is_disconnected
+ }
+
+ fn watch(&self, oper: Operation, cx: &Context) -> bool {
+ let mut inner = self.0.inner.lock();
+ inner.receivers.watch(oper, cx);
+ inner.senders.can_select() || inner.is_disconnected
+ }
+
+ fn unwatch(&self, oper: Operation) {
+ let mut inner = self.0.inner.lock();
+ inner.receivers.unwatch(oper);
+ }
+}
+
+impl<T> SelectHandle for Sender<'_, T> {
+ fn try_select(&self, token: &mut Token) -> bool {
+ self.0.start_send(token)
+ }
+
+ fn deadline(&self) -> Option<Instant> {
+ None
+ }
+
+ fn register(&self, oper: Operation, cx: &Context) -> bool {
+ let packet = Box::into_raw(Packet::<T>::empty_on_heap());
+
+ let mut inner = self.0.inner.lock();
+ inner
+ .senders
+ .register_with_packet(oper, packet as usize, cx);
+ inner.receivers.notify();
+ inner.receivers.can_select() || inner.is_disconnected
+ }
+
+ fn unregister(&self, oper: Operation) {
+ if let Some(operation) = self.0.inner.lock().senders.unregister(oper) {
+ unsafe {
+ drop(Box::from_raw(operation.packet as *mut Packet<T>));
+ }
+ }
+ }
+
+ fn accept(&self, token: &mut Token, cx: &Context) -> bool {
+ token.zero = cx.wait_packet();
+ true
+ }
+
+ fn is_ready(&self) -> bool {
+ let inner = self.0.inner.lock();
+ inner.receivers.can_select() || inner.is_disconnected
+ }
+
+ fn watch(&self, oper: Operation, cx: &Context) -> bool {
+ let mut inner = self.0.inner.lock();
+ inner.senders.watch(oper, cx);
+ inner.receivers.can_select() || inner.is_disconnected
+ }
+
+ fn unwatch(&self, oper: Operation) {
+ let mut inner = self.0.inner.lock();
+ inner.senders.unwatch(oper);
+ }
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..e08ac08
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,368 @@
+//! Multi-producer multi-consumer channels for message passing.
+//!
+//! This crate is an alternative to [`std::sync::mpsc`] with more features and better performance.
+//!
+//! # Hello, world!
+//!
+//! ```
+//! use crossbeam_channel::unbounded;
+//!
+//! // Create a channel of unbounded capacity.
+//! let (s, r) = unbounded();
+//!
+//! // Send a message into the channel.
+//! s.send("Hello, world!").unwrap();
+//!
+//! // Receive the message from the channel.
+//! assert_eq!(r.recv(), Ok("Hello, world!"));
+//! ```
+//!
+//! # Channel types
+//!
+//! Channels can be created using two functions:
+//!
+//! * [`bounded`] creates a channel of bounded capacity, i.e. there is a limit to how many messages
+//! it can hold at a time.
+//!
+//! * [`unbounded`] creates a channel of unbounded capacity, i.e. it can hold any number of
+//! messages at a time.
+//!
+//! Both functions return a [`Sender`] and a [`Receiver`], which represent the two opposite sides
+//! of a channel.
+//!
+//! Creating a bounded channel:
+//!
+//! ```
+//! use crossbeam_channel::bounded;
+//!
+//! // Create a channel that can hold at most 5 messages at a time.
+//! let (s, r) = bounded(5);
+//!
+//! // Can send only 5 messages without blocking.
+//! for i in 0..5 {
+//! s.send(i).unwrap();
+//! }
+//!
+//! // Another call to `send` would block because the channel is full.
+//! // s.send(5).unwrap();
+//! ```
+//!
+//! Creating an unbounded channel:
+//!
+//! ```
+//! use crossbeam_channel::unbounded;
+//!
+//! // Create an unbounded channel.
+//! let (s, r) = unbounded();
+//!
+//! // Can send any number of messages into the channel without blocking.
+//! for i in 0..1000 {
+//! s.send(i).unwrap();
+//! }
+//! ```
+//!
+//! A special case is zero-capacity channel, which cannot hold any messages. Instead, send and
+//! receive operations must appear at the same time in order to pair up and pass the message over:
+//!
+//! ```
+//! use std::thread;
+//! use crossbeam_channel::bounded;
+//!
+//! // Create a zero-capacity channel.
+//! let (s, r) = bounded(0);
+//!
+//! // Sending blocks until a receive operation appears on the other side.
+//! thread::spawn(move || s.send("Hi!").unwrap());
+//!
+//! // Receiving blocks until a send operation appears on the other side.
+//! assert_eq!(r.recv(), Ok("Hi!"));
+//! ```
+//!
+//! # Sharing channels
+//!
+//! Senders and receivers can be cloned and sent to other threads:
+//!
+//! ```
+//! use std::thread;
+//! use crossbeam_channel::bounded;
+//!
+//! let (s1, r1) = bounded(0);
+//! let (s2, r2) = (s1.clone(), r1.clone());
+//!
+//! // Spawn a thread that receives a message and then sends one.
+//! thread::spawn(move || {
+//! r2.recv().unwrap();
+//! s2.send(2).unwrap();
+//! });
+//!
+//! // Send a message and then receive one.
+//! s1.send(1).unwrap();
+//! r1.recv().unwrap();
+//! ```
+//!
+//! Note that cloning only creates a new handle to the same sending or receiving side. It does not
+//! create a separate stream of messages in any way:
+//!
+//! ```
+//! use crossbeam_channel::unbounded;
+//!
+//! let (s1, r1) = unbounded();
+//! let (s2, r2) = (s1.clone(), r1.clone());
+//! let (s3, r3) = (s2.clone(), r2.clone());
+//!
+//! s1.send(10).unwrap();
+//! s2.send(20).unwrap();
+//! s3.send(30).unwrap();
+//!
+//! assert_eq!(r3.recv(), Ok(10));
+//! assert_eq!(r1.recv(), Ok(20));
+//! assert_eq!(r2.recv(), Ok(30));
+//! ```
+//!
+//! It's also possible to share senders and receivers by reference:
+//!
+//! ```
+//! use crossbeam_channel::bounded;
+//! use crossbeam_utils::thread::scope;
+//!
+//! let (s, r) = bounded(0);
+//!
+//! scope(|scope| {
+//! // Spawn a thread that receives a message and then sends one.
+//! scope.spawn(|_| {
+//! r.recv().unwrap();
+//! s.send(2).unwrap();
+//! });
+//!
+//! // Send a message and then receive one.
+//! s.send(1).unwrap();
+//! r.recv().unwrap();
+//! }).unwrap();
+//! ```
+//!
+//! # Disconnection
+//!
+//! When all senders or all receivers associated with a channel get dropped, the channel becomes
+//! disconnected. No more messages can be sent, but any remaining messages can still be received.
+//! Send and receive operations on a disconnected channel never block.
+//!
+//! ```
+//! use crossbeam_channel::{unbounded, RecvError};
+//!
+//! let (s, r) = unbounded();
+//! s.send(1).unwrap();
+//! s.send(2).unwrap();
+//! s.send(3).unwrap();
+//!
+//! // The only sender is dropped, disconnecting the channel.
+//! drop(s);
+//!
+//! // The remaining messages can be received.
+//! assert_eq!(r.recv(), Ok(1));
+//! assert_eq!(r.recv(), Ok(2));
+//! assert_eq!(r.recv(), Ok(3));
+//!
+//! // There are no more messages in the channel.
+//! assert!(r.is_empty());
+//!
+//! // Note that calling `r.recv()` does not block.
+//! // Instead, `Err(RecvError)` is returned immediately.
+//! assert_eq!(r.recv(), Err(RecvError));
+//! ```
+//!
+//! # Blocking operations
+//!
+//! Send and receive operations come in three flavors:
+//!
+//! * Non-blocking (returns immediately with success or failure).
+//! * Blocking (waits until the operation succeeds or the channel becomes disconnected).
+//! * Blocking with a timeout (blocks only for a certain duration of time).
+//!
+//! A simple example showing the difference between non-blocking and blocking operations:
+//!
+//! ```
+//! use crossbeam_channel::{bounded, RecvError, TryRecvError};
+//!
+//! let (s, r) = bounded(1);
+//!
+//! // Send a message into the channel.
+//! s.send("foo").unwrap();
+//!
+//! // This call would block because the channel is full.
+//! // s.send("bar").unwrap();
+//!
+//! // Receive the message.
+//! assert_eq!(r.recv(), Ok("foo"));
+//!
+//! // This call would block because the channel is empty.
+//! // r.recv();
+//!
+//! // Try receiving a message without blocking.
+//! assert_eq!(r.try_recv(), Err(TryRecvError::Empty));
+//!
+//! // Disconnect the channel.
+//! drop(s);
+//!
+//! // This call doesn't block because the channel is now disconnected.
+//! assert_eq!(r.recv(), Err(RecvError));
+//! ```
+//!
+//! # Iteration
+//!
+//! Receivers can be used as iterators. For example, method [`iter`] creates an iterator that
+//! receives messages until the channel becomes empty and disconnected. Note that iteration may
+//! block waiting for next message to arrive.
+//!
+//! ```
+//! use std::thread;
+//! use crossbeam_channel::unbounded;
+//!
+//! let (s, r) = unbounded();
+//!
+//! thread::spawn(move || {
+//! s.send(1).unwrap();
+//! s.send(2).unwrap();
+//! s.send(3).unwrap();
+//! drop(s); // Disconnect the channel.
+//! });
+//!
+//! // Collect all messages from the channel.
+//! // Note that the call to `collect` blocks until the sender is dropped.
+//! let v: Vec<_> = r.iter().collect();
+//!
+//! assert_eq!(v, [1, 2, 3]);
+//! ```
+//!
+//! A non-blocking iterator can be created using [`try_iter`], which receives all available
+//! messages without blocking:
+//!
+//! ```
+//! use crossbeam_channel::unbounded;
+//!
+//! let (s, r) = unbounded();
+//! s.send(1).unwrap();
+//! s.send(2).unwrap();
+//! s.send(3).unwrap();
+//! // No need to drop the sender.
+//!
+//! // Receive all messages currently in the channel.
+//! let v: Vec<_> = r.try_iter().collect();
+//!
+//! assert_eq!(v, [1, 2, 3]);
+//! ```
+//!
+//! # Selection
+//!
+//! The [`select!`] macro allows you to define a set of channel operations, wait until any one of
+//! them becomes ready, and finally execute it. If multiple operations are ready at the same time,
+//! a random one among them is selected.
+//!
+//! It is also possible to define a `default` case that gets executed if none of the operations are
+//! ready, either right away or for a certain duration of time.
+//!
+//! An operation is considered to be ready if it doesn't have to block. Note that it is ready even
+//! when it will simply return an error because the channel is disconnected.
+//!
+//! An example of receiving a message from two channels:
+//!
+//! ```
+//! use std::thread;
+//! use std::time::Duration;
+//! use crossbeam_channel::{select, unbounded};
+//!
+//! let (s1, r1) = unbounded();
+//! let (s2, r2) = unbounded();
+//!
+//! thread::spawn(move || s1.send(10).unwrap());
+//! thread::spawn(move || s2.send(20).unwrap());
+//!
+//! // At most one of these two receive operations will be executed.
+//! select! {
+//! recv(r1) -> msg => assert_eq!(msg, Ok(10)),
+//! recv(r2) -> msg => assert_eq!(msg, Ok(20)),
+//! default(Duration::from_secs(1)) => println!("timed out"),
+//! }
+//! ```
+//!
+//! If you need to select over a dynamically created list of channel operations, use [`Select`]
+//! instead. The [`select!`] macro is just a convenience wrapper around [`Select`].
+//!
+//! # Extra channels
+//!
+//! Three functions can create special kinds of channels, all of which return just a [`Receiver`]
+//! handle:
+//!
+//! * [`after`] creates a channel that delivers a single message after a certain duration of time.
+//! * [`tick`] creates a channel that delivers messages periodically.
+//! * [`never`] creates a channel that never delivers messages.
+//!
+//! These channels are very efficient because messages get lazily generated on receive operations.
+//!
+//! An example that prints elapsed time every 50 milliseconds for the duration of 1 second:
+//!
+//! ```
+//! use std::time::{Duration, Instant};
+//! use crossbeam_channel::{after, select, tick};
+//!
+//! let start = Instant::now();
+//! let ticker = tick(Duration::from_millis(50));
+//! let timeout = after(Duration::from_secs(1));
+//!
+//! loop {
+//! select! {
+//! recv(ticker) -> _ => println!("elapsed: {:?}", start.elapsed()),
+//! recv(timeout) -> _ => break,
+//! }
+//! }
+//! ```
+//!
+//! [`send`]: Sender::send
+//! [`recv`]: Receiver::recv
+//! [`iter`]: Receiver::iter
+//! [`try_iter`]: Receiver::try_iter
+
+#![doc(test(
+ no_crate_inject,
+ attr(
+ deny(warnings, rust_2018_idioms),
+ allow(dead_code, unused_assignments, unused_variables)
+ )
+))]
+#![warn(missing_docs, missing_debug_implementations, rust_2018_idioms)]
+#![cfg_attr(not(feature = "std"), no_std)]
+// matches! requires Rust 1.42
+#![allow(clippy::match_like_matches_macro)]
+
+use cfg_if::cfg_if;
+
+cfg_if! {
+ if #[cfg(feature = "std")] {
+ mod channel;
+ mod context;
+ mod counter;
+ mod err;
+ mod flavors;
+ mod select;
+ mod select_macro;
+ mod utils;
+ mod waker;
+
+ /// Crate internals used by the `select!` macro.
+ #[doc(hidden)]
+ pub mod internal {
+ pub use crate::select::SelectHandle;
+ pub use crate::select::{select, select_timeout, try_select};
+ }
+
+ pub use crate::channel::{after, at, never, tick};
+ pub use crate::channel::{bounded, unbounded};
+ pub use crate::channel::{IntoIter, Iter, TryIter};
+ pub use crate::channel::{Receiver, Sender};
+
+ pub use crate::select::{Select, SelectedOperation};
+
+ pub use crate::err::{ReadyTimeoutError, SelectTimeoutError, TryReadyError, TrySelectError};
+ pub use crate::err::{RecvError, RecvTimeoutError, TryRecvError};
+ pub use crate::err::{SendError, SendTimeoutError, TrySendError};
+ }
+}
diff --git a/src/select.rs b/src/select.rs
new file mode 100644
index 0000000..1488f80
--- /dev/null
+++ b/src/select.rs
@@ -0,0 +1,1251 @@
+//! Interface to the select mechanism.
+
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem;
+use std::time::{Duration, Instant};
+
+use crossbeam_utils::Backoff;
+
+use crate::channel::{self, Receiver, Sender};
+use crate::context::Context;
+use crate::err::{ReadyTimeoutError, TryReadyError};
+use crate::err::{RecvError, SendError};
+use crate::err::{SelectTimeoutError, TrySelectError};
+use crate::flavors;
+use crate::utils;
+
+/// Temporary data that gets initialized during select or a blocking operation, and is consumed by
+/// `read` or `write`.
+///
+/// Each field contains data associated with a specific channel flavor.
+#[derive(Debug, Default)]
+pub struct Token {
+ pub at: flavors::at::AtToken,
+ pub array: flavors::array::ArrayToken,
+ pub list: flavors::list::ListToken,
+ pub never: flavors::never::NeverToken,
+ pub tick: flavors::tick::TickToken,
+ pub zero: flavors::zero::ZeroToken,
+}
+
+/// Identifier associated with an operation by a specific thread on a specific channel.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Operation(usize);
+
+impl Operation {
+ /// Creates an operation identifier from a mutable reference.
+ ///
+ /// This function essentially just turns the address of the reference into a number. The
+ /// reference should point to a variable that is specific to the thread and the operation,
+ /// and is alive for the entire duration of select or blocking operation.
+ #[inline]
+ pub fn hook<T>(r: &mut T) -> Operation {
+ let val = r as *mut T as usize;
+ // Make sure that the pointer address doesn't equal the numerical representation of
+ // `Selected::{Waiting, Aborted, Disconnected}`.
+ assert!(val > 2);
+ Operation(val)
+ }
+}
+
+/// Current state of a select or a blocking operation.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Selected {
+ /// Still waiting for an operation.
+ Waiting,
+
+ /// The attempt to block the current thread has been aborted.
+ Aborted,
+
+ /// An operation became ready because a channel is disconnected.
+ Disconnected,
+
+ /// An operation became ready because a message can be sent or received.
+ Operation(Operation),
+}
+
+impl From<usize> for Selected {
+ #[inline]
+ fn from(val: usize) -> Selected {
+ match val {
+ 0 => Selected::Waiting,
+ 1 => Selected::Aborted,
+ 2 => Selected::Disconnected,
+ oper => Selected::Operation(Operation(oper)),
+ }
+ }
+}
+
+impl Into<usize> for Selected {
+ #[inline]
+ fn into(self) -> usize {
+ match self {
+ Selected::Waiting => 0,
+ Selected::Aborted => 1,
+ Selected::Disconnected => 2,
+ Selected::Operation(Operation(val)) => val,
+ }
+ }
+}
+
+/// A receiver or a sender that can participate in select.
+///
+/// This is a handle that assists select in executing an operation, registration, deciding on the
+/// appropriate deadline for blocking, etc.
+pub trait SelectHandle {
+ /// Attempts to select an operation and returns `true` on success.
+ fn try_select(&self, token: &mut Token) -> bool;
+
+ /// Returns a deadline for an operation, if there is one.
+ fn deadline(&self) -> Option<Instant>;
+
+ /// Registers an operation for execution and returns `true` if it is now ready.
+ fn register(&self, oper: Operation, cx: &Context) -> bool;
+
+ /// Unregisters an operation for execution.
+ fn unregister(&self, oper: Operation);
+
+ /// Attempts to select an operation the thread got woken up for and returns `true` on success.
+ fn accept(&self, token: &mut Token, cx: &Context) -> bool;
+
+ /// Returns `true` if an operation can be executed without blocking.
+ fn is_ready(&self) -> bool;
+
+ /// Registers an operation for readiness notification and returns `true` if it is now ready.
+ fn watch(&self, oper: Operation, cx: &Context) -> bool;
+
+ /// Unregisters an operation for readiness notification.
+ fn unwatch(&self, oper: Operation);
+}
+
+impl<T: SelectHandle> SelectHandle for &T {
+ fn try_select(&self, token: &mut Token) -> bool {
+ (**self).try_select(token)
+ }
+
+ fn deadline(&self) -> Option<Instant> {
+ (**self).deadline()
+ }
+
+ fn register(&self, oper: Operation, cx: &Context) -> bool {
+ (**self).register(oper, cx)
+ }
+
+ fn unregister(&self, oper: Operation) {
+ (**self).unregister(oper);
+ }
+
+ fn accept(&self, token: &mut Token, cx: &Context) -> bool {
+ (**self).accept(token, cx)
+ }
+
+ fn is_ready(&self) -> bool {
+ (**self).is_ready()
+ }
+
+ fn watch(&self, oper: Operation, cx: &Context) -> bool {
+ (**self).watch(oper, cx)
+ }
+
+ fn unwatch(&self, oper: Operation) {
+ (**self).unwatch(oper)
+ }
+}
+
+/// Determines when a select operation should time out.
+#[derive(Clone, Copy, Eq, PartialEq)]
+enum Timeout {
+ /// No blocking.
+ Now,
+
+ /// Block forever.
+ Never,
+
+ /// Time out after the time instant.
+ At(Instant),
+}
+
+/// Runs until one of the operations is selected, potentially blocking the current thread.
+///
+/// Successful receive operations will have to be followed up by `channel::read()` and successful
+/// send operations by `channel::write()`.
+fn run_select(
+ handles: &mut [(&dyn SelectHandle, usize, *const u8)],
+ timeout: Timeout,
+) -> Option<(Token, usize, *const u8)> {
+ if handles.is_empty() {
+ // Wait until the timeout and return.
+ match timeout {
+ Timeout::Now => return None,
+ Timeout::Never => {
+ utils::sleep_until(None);
+ unreachable!();
+ }
+ Timeout::At(when) => {
+ utils::sleep_until(Some(when));
+ return None;
+ }
+ }
+ }
+
+ // Shuffle the operations for fairness.
+ utils::shuffle(handles);
+
+ // Create a token, which serves as a temporary variable that gets initialized in this function
+ // and is later used by a call to `channel::read()` or `channel::write()` that completes the
+ // selected operation.
+ let mut token = Token::default();
+
+ // Try selecting one of the operations without blocking.
+ for &(handle, i, ptr) in handles.iter() {
+ if handle.try_select(&mut token) {
+ return Some((token, i, ptr));
+ }
+ }
+
+ loop {
+ // Prepare for blocking.
+ let res = Context::with(|cx| {
+ let mut sel = Selected::Waiting;
+ let mut registered_count = 0;
+ let mut index_ready = None;
+
+ if let Timeout::Now = timeout {
+ cx.try_select(Selected::Aborted).unwrap();
+ }
+
+ // Register all operations.
+ for (handle, i, _) in handles.iter_mut() {
+ registered_count += 1;
+
+ // If registration returns `false`, that means the operation has just become ready.
+ if handle.register(Operation::hook::<&dyn SelectHandle>(handle), cx) {
+ // Try aborting select.
+ sel = match cx.try_select(Selected::Aborted) {
+ Ok(()) => {
+ index_ready = Some(*i);
+ Selected::Aborted
+ }
+ Err(s) => s,
+ };
+ break;
+ }
+
+ // If another thread has already selected one of the operations, stop registration.
+ sel = cx.selected();
+ if sel != Selected::Waiting {
+ break;
+ }
+ }
+
+ if sel == Selected::Waiting {
+ // Check with each operation for how long we're allowed to block, and compute the
+ // earliest deadline.
+ let mut deadline: Option<Instant> = match timeout {
+ Timeout::Now => return None,
+ Timeout::Never => None,
+ Timeout::At(when) => Some(when),
+ };
+ for &(handle, _, _) in handles.iter() {
+ if let Some(x) = handle.deadline() {
+ deadline = deadline.map(|y| x.min(y)).or(Some(x));
+ }
+ }
+
+ // Block the current thread.
+ sel = cx.wait_until(deadline);
+ }
+
+ // Unregister all registered operations.
+ for (handle, _, _) in handles.iter_mut().take(registered_count) {
+ handle.unregister(Operation::hook::<&dyn SelectHandle>(handle));
+ }
+
+ match sel {
+ Selected::Waiting => unreachable!(),
+ Selected::Aborted => {
+ // If an operation became ready during registration, try selecting it.
+ if let Some(index_ready) = index_ready {
+ for &(handle, i, ptr) in handles.iter() {
+ if i == index_ready && handle.try_select(&mut token) {
+ return Some((i, ptr));
+ }
+ }
+ }
+ }
+ Selected::Disconnected => {}
+ Selected::Operation(_) => {
+ // Find the selected operation.
+ for (handle, i, ptr) in handles.iter_mut() {
+ // Is this the selected operation?
+ if sel == Selected::Operation(Operation::hook::<&dyn SelectHandle>(handle))
+ {
+ // Try selecting this operation.
+ if handle.accept(&mut token, cx) {
+ return Some((*i, *ptr));
+ }
+ }
+ }
+ }
+ }
+
+ None
+ });
+
+ // Return if an operation was selected.
+ if let Some((i, ptr)) = res {
+ return Some((token, i, ptr));
+ }
+
+ // Try selecting one of the operations without blocking.
+ for &(handle, i, ptr) in handles.iter() {
+ if handle.try_select(&mut token) {
+ return Some((token, i, ptr));
+ }
+ }
+
+ match timeout {
+ Timeout::Now => return None,
+ Timeout::Never => {}
+ Timeout::At(when) => {
+ if Instant::now() >= when {
+ return None;
+ }
+ }
+ }
+ }
+}
+
+/// Runs until one of the operations becomes ready, potentially blocking the current thread.
+fn run_ready(
+ handles: &mut [(&dyn SelectHandle, usize, *const u8)],
+ timeout: Timeout,
+) -> Option<usize> {
+ if handles.is_empty() {
+ // Wait until the timeout and return.
+ match timeout {
+ Timeout::Now => return None,
+ Timeout::Never => {
+ utils::sleep_until(None);
+ unreachable!();
+ }
+ Timeout::At(when) => {
+ utils::sleep_until(Some(when));
+ return None;
+ }
+ }
+ }
+
+ // Shuffle the operations for fairness.
+ utils::shuffle(handles);
+
+ loop {
+ let backoff = Backoff::new();
+ loop {
+ // Check operations for readiness.
+ for &(handle, i, _) in handles.iter() {
+ if handle.is_ready() {
+ return Some(i);
+ }
+ }
+
+ if backoff.is_completed() {
+ break;
+ } else {
+ backoff.snooze();
+ }
+ }
+
+ // Check for timeout.
+ match timeout {
+ Timeout::Now => return None,
+ Timeout::Never => {}
+ Timeout::At(when) => {
+ if Instant::now() >= when {
+ return None;
+ }
+ }
+ }
+
+ // Prepare for blocking.
+ let res = Context::with(|cx| {
+ let mut sel = Selected::Waiting;
+ let mut registered_count = 0;
+
+ // Begin watching all operations.
+ for (handle, _, _) in handles.iter_mut() {
+ registered_count += 1;
+ let oper = Operation::hook::<&dyn SelectHandle>(handle);
+
+ // If registration returns `false`, that means the operation has just become ready.
+ if handle.watch(oper, cx) {
+ sel = match cx.try_select(Selected::Operation(oper)) {
+ Ok(()) => Selected::Operation(oper),
+ Err(s) => s,
+ };
+ break;
+ }
+
+ // If another thread has already chosen one of the operations, stop registration.
+ sel = cx.selected();
+ if sel != Selected::Waiting {
+ break;
+ }
+ }
+
+ if sel == Selected::Waiting {
+ // Check with each operation for how long we're allowed to block, and compute the
+ // earliest deadline.
+ let mut deadline: Option<Instant> = match timeout {
+ Timeout::Now => unreachable!(),
+ Timeout::Never => None,
+ Timeout::At(when) => Some(when),
+ };
+ for &(handle, _, _) in handles.iter() {
+ if let Some(x) = handle.deadline() {
+ deadline = deadline.map(|y| x.min(y)).or(Some(x));
+ }
+ }
+
+ // Block the current thread.
+ sel = cx.wait_until(deadline);
+ }
+
+ // Unwatch all operations.
+ for (handle, _, _) in handles.iter_mut().take(registered_count) {
+ handle.unwatch(Operation::hook::<&dyn SelectHandle>(handle));
+ }
+
+ match sel {
+ Selected::Waiting => unreachable!(),
+ Selected::Aborted => {}
+ Selected::Disconnected => {}
+ Selected::Operation(_) => {
+ for (handle, i, _) in handles.iter_mut() {
+ let oper = Operation::hook::<&dyn SelectHandle>(handle);
+ if sel == Selected::Operation(oper) {
+ return Some(*i);
+ }
+ }
+ }
+ }
+
+ None
+ });
+
+ // Return if an operation became ready.
+ if res.is_some() {
+ return res;
+ }
+ }
+}
+
+/// Attempts to select one of the operations without blocking.
+#[inline]
+pub fn try_select<'a>(
+ handles: &mut [(&'a dyn SelectHandle, usize, *const u8)],
+) -> Result<SelectedOperation<'a>, TrySelectError> {
+ match run_select(handles, Timeout::Now) {
+ None => Err(TrySelectError),
+ Some((token, index, ptr)) => Ok(SelectedOperation {
+ token,
+ index,
+ ptr,
+ _marker: PhantomData,
+ }),
+ }
+}
+
+/// Blocks until one of the operations becomes ready and selects it.
+#[inline]
+pub fn select<'a>(
+ handles: &mut [(&'a dyn SelectHandle, usize, *const u8)],
+) -> SelectedOperation<'a> {
+ if handles.is_empty() {
+ panic!("no operations have been added to `Select`");
+ }
+
+ let (token, index, ptr) = run_select(handles, Timeout::Never).unwrap();
+ SelectedOperation {
+ token,
+ index,
+ ptr,
+ _marker: PhantomData,
+ }
+}
+
+/// Blocks for a limited time until one of the operations becomes ready and selects it.
+#[inline]
+pub fn select_timeout<'a>(
+ handles: &mut [(&'a dyn SelectHandle, usize, *const u8)],
+ timeout: Duration,
+) -> Result<SelectedOperation<'a>, SelectTimeoutError> {
+ select_deadline(handles, Instant::now() + timeout)
+}
+
+/// Blocks until a given deadline, or until one of the operations becomes ready and selects it.
+#[inline]
+pub fn select_deadline<'a>(
+ handles: &mut [(&'a dyn SelectHandle, usize, *const u8)],
+ deadline: Instant,
+) -> Result<SelectedOperation<'a>, SelectTimeoutError> {
+ match run_select(handles, Timeout::At(deadline)) {
+ None => Err(SelectTimeoutError),
+ Some((token, index, ptr)) => Ok(SelectedOperation {
+ token,
+ index,
+ ptr,
+ _marker: PhantomData,
+ }),
+ }
+}
+
+/// Selects from a set of channel operations.
+///
+/// `Select` allows you to define a set of channel operations, wait until any one of them becomes
+/// ready, and finally execute it. If multiple operations are ready at the same time, a random one
+/// among them is selected.
+///
+/// An operation is considered to be ready if it doesn't have to block. Note that it is ready even
+/// when it will simply return an error because the channel is disconnected.
+///
+/// The [`select!`] macro is a convenience wrapper around `Select`. However, it cannot select over a
+/// dynamically created list of channel operations.
+///
+/// Once a list of operations has been built with `Select`, there are two different ways of
+/// proceeding:
+///
+/// * Select an operation with [`try_select`], [`select`], or [`select_timeout`]. If successful,
+/// the returned selected operation has already begun and **must** be completed. If we don't
+/// complete it, a panic will occur.
+///
+/// * Wait for an operation to become ready with [`try_ready`], [`ready`], or [`ready_timeout`]. If
+/// successful, we may attempt to execute the operation, but are not obliged to. In fact, it's
+/// possible for another thread to make the operation not ready just before we try executing it,
+/// so it's wise to use a retry loop. However, note that these methods might return with success
+/// spuriously, so it's a good idea to always double check if the operation is really ready.
+///
+/// # Examples
+///
+/// Use [`select`] to receive a message from a list of receivers:
+///
+/// ```
+/// use crossbeam_channel::{Receiver, RecvError, Select};
+///
+/// fn recv_multiple<T>(rs: &[Receiver<T>]) -> Result<T, RecvError> {
+/// // Build a list of operations.
+/// let mut sel = Select::new();
+/// for r in rs {
+/// sel.recv(r);
+/// }
+///
+/// // Complete the selected operation.
+/// let oper = sel.select();
+/// let index = oper.index();
+/// oper.recv(&rs[index])
+/// }
+/// ```
+///
+/// Use [`ready`] to receive a message from a list of receivers:
+///
+/// ```
+/// use crossbeam_channel::{Receiver, RecvError, Select};
+///
+/// fn recv_multiple<T>(rs: &[Receiver<T>]) -> Result<T, RecvError> {
+/// // Build a list of operations.
+/// let mut sel = Select::new();
+/// for r in rs {
+/// sel.recv(r);
+/// }
+///
+/// loop {
+/// // Wait until a receive operation becomes ready and try executing it.
+/// let index = sel.ready();
+/// let res = rs[index].try_recv();
+///
+/// // If the operation turns out not to be ready, retry.
+/// if let Err(e) = res {
+/// if e.is_empty() {
+/// continue;
+/// }
+/// }
+///
+/// // Success!
+/// return res.map_err(|_| RecvError);
+/// }
+/// }
+/// ```
+///
+/// [`try_select`]: Select::try_select
+/// [`select`]: Select::select
+/// [`select_timeout`]: Select::select_timeout
+/// [`try_ready`]: Select::try_ready
+/// [`ready`]: Select::ready
+/// [`ready_timeout`]: Select::ready_timeout
+pub struct Select<'a> {
+ /// A list of senders and receivers participating in selection.
+ handles: Vec<(&'a dyn SelectHandle, usize, *const u8)>,
+
+ /// The next index to assign to an operation.
+ next_index: usize,
+}
+
+unsafe impl Send for Select<'_> {}
+unsafe impl Sync for Select<'_> {}
+
+impl<'a> Select<'a> {
+ /// Creates an empty list of channel operations for selection.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::Select;
+ ///
+ /// let mut sel = Select::new();
+ ///
+ /// // The list of operations is empty, which means no operation can be selected.
+ /// assert!(sel.try_select().is_err());
+ /// ```
+ pub fn new() -> Select<'a> {
+ Select {
+ handles: Vec::with_capacity(4),
+ next_index: 0,
+ }
+ }
+
+ /// Adds a send operation.
+ ///
+ /// Returns the index of the added operation.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::{unbounded, Select};
+ ///
+ /// let (s, r) = unbounded::<i32>();
+ ///
+ /// let mut sel = Select::new();
+ /// let index = sel.send(&s);
+ /// ```
+ pub fn send<T>(&mut self, s: &'a Sender<T>) -> usize {
+ let i = self.next_index;
+ let ptr = s as *const Sender<_> as *const u8;
+ self.handles.push((s, i, ptr));
+ self.next_index += 1;
+ i
+ }
+
+ /// Adds a receive operation.
+ ///
+ /// Returns the index of the added operation.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::{unbounded, Select};
+ ///
+ /// let (s, r) = unbounded::<i32>();
+ ///
+ /// let mut sel = Select::new();
+ /// let index = sel.recv(&r);
+ /// ```
+ pub fn recv<T>(&mut self, r: &'a Receiver<T>) -> usize {
+ let i = self.next_index;
+ let ptr = r as *const Receiver<_> as *const u8;
+ self.handles.push((r, i, ptr));
+ self.next_index += 1;
+ i
+ }
+
+ /// Removes a previously added operation.
+ ///
+ /// This is useful when an operation is selected because the channel got disconnected and we
+ /// want to try again to select a different operation instead.
+ ///
+ /// If new operations are added after removing some, the indices of removed operations will not
+ /// be reused.
+ ///
+ /// # Panics
+ ///
+ /// An attempt to remove a non-existing or already removed operation will panic.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::{unbounded, Select};
+ ///
+ /// let (s1, r1) = unbounded::<i32>();
+ /// let (_, r2) = unbounded::<i32>();
+ ///
+ /// let mut sel = Select::new();
+ /// let oper1 = sel.recv(&r1);
+ /// let oper2 = sel.recv(&r2);
+ ///
+ /// // Both operations are initially ready, so a random one will be executed.
+ /// let oper = sel.select();
+ /// assert_eq!(oper.index(), oper2);
+ /// assert!(oper.recv(&r2).is_err());
+ /// sel.remove(oper2);
+ ///
+ /// s1.send(10).unwrap();
+ ///
+ /// let oper = sel.select();
+ /// assert_eq!(oper.index(), oper1);
+ /// assert_eq!(oper.recv(&r1), Ok(10));
+ /// ```
+ pub fn remove(&mut self, index: usize) {
+ assert!(
+ index < self.next_index,
+ "index out of bounds; {} >= {}",
+ index,
+ self.next_index,
+ );
+
+ let i = self
+ .handles
+ .iter()
+ .enumerate()
+ .find(|(_, (_, i, _))| *i == index)
+ .expect("no operation with this index")
+ .0;
+
+ self.handles.swap_remove(i);
+ }
+
+ /// Attempts to select one of the operations without blocking.
+ ///
+ /// If an operation is ready, it is selected and returned. If multiple operations are ready at
+ /// the same time, a random one among them is selected. If none of the operations are ready, an
+ /// error is returned.
+ ///
+ /// An operation is considered to be ready if it doesn't have to block. Note that it is ready
+ /// even when it will simply return an error because the channel is disconnected.
+ ///
+ /// The selected operation must be completed with [`SelectedOperation::send`]
+ /// or [`SelectedOperation::recv`].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::{unbounded, Select};
+ ///
+ /// let (s1, r1) = unbounded();
+ /// let (s2, r2) = unbounded();
+ ///
+ /// s1.send(10).unwrap();
+ /// s2.send(20).unwrap();
+ ///
+ /// let mut sel = Select::new();
+ /// let oper1 = sel.recv(&r1);
+ /// let oper2 = sel.recv(&r2);
+ ///
+ /// // Both operations are initially ready, so a random one will be executed.
+ /// let oper = sel.try_select();
+ /// match oper {
+ /// Err(_) => panic!("both operations should be ready"),
+ /// Ok(oper) => match oper.index() {
+ /// i if i == oper1 => assert_eq!(oper.recv(&r1), Ok(10)),
+ /// i if i == oper2 => assert_eq!(oper.recv(&r2), Ok(20)),
+ /// _ => unreachable!(),
+ /// }
+ /// }
+ /// ```
+ pub fn try_select(&mut self) -> Result<SelectedOperation<'a>, TrySelectError> {
+ try_select(&mut self.handles)
+ }
+
+ /// Blocks until one of the operations becomes ready and selects it.
+ ///
+ /// Once an operation becomes ready, it is selected and returned. If multiple operations are
+ /// ready at the same time, a random one among them is selected.
+ ///
+ /// An operation is considered to be ready if it doesn't have to block. Note that it is ready
+ /// even when it will simply return an error because the channel is disconnected.
+ ///
+ /// The selected operation must be completed with [`SelectedOperation::send`]
+ /// or [`SelectedOperation::recv`].
+ ///
+ /// # Panics
+ ///
+ /// Panics if no operations have been added to `Select`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::Duration;
+ /// use crossbeam_channel::{unbounded, Select};
+ ///
+ /// let (s1, r1) = unbounded();
+ /// let (s2, r2) = unbounded();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_secs(1));
+ /// s1.send(10).unwrap();
+ /// });
+ /// thread::spawn(move || s2.send(20).unwrap());
+ ///
+ /// let mut sel = Select::new();
+ /// let oper1 = sel.recv(&r1);
+ /// let oper2 = sel.recv(&r2);
+ ///
+ /// // The second operation will be selected because it becomes ready first.
+ /// let oper = sel.select();
+ /// match oper.index() {
+ /// i if i == oper1 => assert_eq!(oper.recv(&r1), Ok(10)),
+ /// i if i == oper2 => assert_eq!(oper.recv(&r2), Ok(20)),
+ /// _ => unreachable!(),
+ /// }
+ /// ```
+ pub fn select(&mut self) -> SelectedOperation<'a> {
+ select(&mut self.handles)
+ }
+
+ /// Blocks for a limited time until one of the operations becomes ready and selects it.
+ ///
+ /// If an operation becomes ready, it is selected and returned. If multiple operations are
+ /// ready at the same time, a random one among them is selected. If none of the operations
+ /// become ready for the specified duration, an error is returned.
+ ///
+ /// An operation is considered to be ready if it doesn't have to block. Note that it is ready
+ /// even when it will simply return an error because the channel is disconnected.
+ ///
+ /// The selected operation must be completed with [`SelectedOperation::send`]
+ /// or [`SelectedOperation::recv`].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::Duration;
+ /// use crossbeam_channel::{unbounded, Select};
+ ///
+ /// let (s1, r1) = unbounded();
+ /// let (s2, r2) = unbounded();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_secs(1));
+ /// s1.send(10).unwrap();
+ /// });
+ /// thread::spawn(move || s2.send(20).unwrap());
+ ///
+ /// let mut sel = Select::new();
+ /// let oper1 = sel.recv(&r1);
+ /// let oper2 = sel.recv(&r2);
+ ///
+ /// // The second operation will be selected because it becomes ready first.
+ /// let oper = sel.select_timeout(Duration::from_millis(500));
+ /// match oper {
+ /// Err(_) => panic!("should not have timed out"),
+ /// Ok(oper) => match oper.index() {
+ /// i if i == oper1 => assert_eq!(oper.recv(&r1), Ok(10)),
+ /// i if i == oper2 => assert_eq!(oper.recv(&r2), Ok(20)),
+ /// _ => unreachable!(),
+ /// }
+ /// }
+ /// ```
+ pub fn select_timeout(
+ &mut self,
+ timeout: Duration,
+ ) -> Result<SelectedOperation<'a>, SelectTimeoutError> {
+ select_timeout(&mut self.handles, timeout)
+ }
+
+ /// Blocks until a given deadline, or until one of the operations becomes ready and selects it.
+ ///
+ /// If an operation becomes ready, it is selected and returned. If multiple operations are
+ /// ready at the same time, a random one among them is selected. If none of the operations
+ /// become ready before the given deadline, an error is returned.
+ ///
+ /// An operation is considered to be ready if it doesn't have to block. Note that it is ready
+ /// even when it will simply return an error because the channel is disconnected.
+ ///
+ /// The selected operation must be completed with [`SelectedOperation::send`]
+ /// or [`SelectedOperation::recv`].
+ ///
+ /// [`SelectedOperation::send`]: struct.SelectedOperation.html#method.send
+ /// [`SelectedOperation::recv`]: struct.SelectedOperation.html#method.recv
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::{Instant, Duration};
+ /// use crossbeam_channel::{unbounded, Select};
+ ///
+ /// let (s1, r1) = unbounded();
+ /// let (s2, r2) = unbounded();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_secs(1));
+ /// s1.send(10).unwrap();
+ /// });
+ /// thread::spawn(move || s2.send(20).unwrap());
+ ///
+ /// let mut sel = Select::new();
+ /// let oper1 = sel.recv(&r1);
+ /// let oper2 = sel.recv(&r2);
+ ///
+ /// let deadline = Instant::now() + Duration::from_millis(500);
+ ///
+ /// // The second operation will be selected because it becomes ready first.
+ /// let oper = sel.select_deadline(deadline);
+ /// match oper {
+ /// Err(_) => panic!("should not have timed out"),
+ /// Ok(oper) => match oper.index() {
+ /// i if i == oper1 => assert_eq!(oper.recv(&r1), Ok(10)),
+ /// i if i == oper2 => assert_eq!(oper.recv(&r2), Ok(20)),
+ /// _ => unreachable!(),
+ /// }
+ /// }
+ /// ```
+ pub fn select_deadline(
+ &mut self,
+ deadline: Instant,
+ ) -> Result<SelectedOperation<'a>, SelectTimeoutError> {
+ select_deadline(&mut self.handles, deadline)
+ }
+
+ /// Attempts to find a ready operation without blocking.
+ ///
+ /// If an operation is ready, its index is returned. If multiple operations are ready at the
+ /// same time, a random one among them is chosen. If none of the operations are ready, an error
+ /// is returned.
+ ///
+ /// An operation is considered to be ready if it doesn't have to block. Note that it is ready
+ /// even when it will simply return an error because the channel is disconnected.
+ ///
+ /// Note that this method might return with success spuriously, so it's a good idea to always
+ /// double check if the operation is really ready.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::{unbounded, Select};
+ ///
+ /// let (s1, r1) = unbounded();
+ /// let (s2, r2) = unbounded();
+ ///
+ /// s1.send(10).unwrap();
+ /// s2.send(20).unwrap();
+ ///
+ /// let mut sel = Select::new();
+ /// let oper1 = sel.recv(&r1);
+ /// let oper2 = sel.recv(&r2);
+ ///
+ /// // Both operations are initially ready, so a random one will be chosen.
+ /// match sel.try_ready() {
+ /// Err(_) => panic!("both operations should be ready"),
+ /// Ok(i) if i == oper1 => assert_eq!(r1.try_recv(), Ok(10)),
+ /// Ok(i) if i == oper2 => assert_eq!(r2.try_recv(), Ok(20)),
+ /// Ok(_) => unreachable!(),
+ /// }
+ /// ```
+ pub fn try_ready(&mut self) -> Result<usize, TryReadyError> {
+ match run_ready(&mut self.handles, Timeout::Now) {
+ None => Err(TryReadyError),
+ Some(index) => Ok(index),
+ }
+ }
+
+ /// Blocks until one of the operations becomes ready.
+ ///
+ /// Once an operation becomes ready, its index is returned. If multiple operations are ready at
+ /// the same time, a random one among them is chosen.
+ ///
+ /// An operation is considered to be ready if it doesn't have to block. Note that it is ready
+ /// even when it will simply return an error because the channel is disconnected.
+ ///
+ /// Note that this method might return with success spuriously, so it's a good idea to always
+ /// double check if the operation is really ready.
+ ///
+ /// # Panics
+ ///
+ /// Panics if no operations have been added to `Select`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::Duration;
+ /// use crossbeam_channel::{unbounded, Select};
+ ///
+ /// let (s1, r1) = unbounded();
+ /// let (s2, r2) = unbounded();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_secs(1));
+ /// s1.send(10).unwrap();
+ /// });
+ /// thread::spawn(move || s2.send(20).unwrap());
+ ///
+ /// let mut sel = Select::new();
+ /// let oper1 = sel.recv(&r1);
+ /// let oper2 = sel.recv(&r2);
+ ///
+ /// // The second operation will be selected because it becomes ready first.
+ /// match sel.ready() {
+ /// i if i == oper1 => assert_eq!(r1.try_recv(), Ok(10)),
+ /// i if i == oper2 => assert_eq!(r2.try_recv(), Ok(20)),
+ /// _ => unreachable!(),
+ /// }
+ /// ```
+ pub fn ready(&mut self) -> usize {
+ if self.handles.is_empty() {
+ panic!("no operations have been added to `Select`");
+ }
+
+ run_ready(&mut self.handles, Timeout::Never).unwrap()
+ }
+
+ /// Blocks for a limited time until one of the operations becomes ready.
+ ///
+ /// If an operation becomes ready, its index is returned. If multiple operations are ready at
+ /// the same time, a random one among them is chosen. If none of the operations become ready
+ /// for the specified duration, an error is returned.
+ ///
+ /// An operation is considered to be ready if it doesn't have to block. Note that it is ready
+ /// even when it will simply return an error because the channel is disconnected.
+ ///
+ /// Note that this method might return with success spuriously, so it's a good idea to double
+ /// check if the operation is really ready.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::Duration;
+ /// use crossbeam_channel::{unbounded, Select};
+ ///
+ /// let (s1, r1) = unbounded();
+ /// let (s2, r2) = unbounded();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_secs(1));
+ /// s1.send(10).unwrap();
+ /// });
+ /// thread::spawn(move || s2.send(20).unwrap());
+ ///
+ /// let mut sel = Select::new();
+ /// let oper1 = sel.recv(&r1);
+ /// let oper2 = sel.recv(&r2);
+ ///
+ /// // The second operation will be selected because it becomes ready first.
+ /// match sel.ready_timeout(Duration::from_millis(500)) {
+ /// Err(_) => panic!("should not have timed out"),
+ /// Ok(i) if i == oper1 => assert_eq!(r1.try_recv(), Ok(10)),
+ /// Ok(i) if i == oper2 => assert_eq!(r2.try_recv(), Ok(20)),
+ /// Ok(_) => unreachable!(),
+ /// }
+ /// ```
+ pub fn ready_timeout(&mut self, timeout: Duration) -> Result<usize, ReadyTimeoutError> {
+ self.ready_deadline(Instant::now() + timeout)
+ }
+
+ /// Blocks until a given deadline, or until one of the operations becomes ready.
+ ///
+ /// If an operation becomes ready, its index is returned. If multiple operations are ready at
+ /// the same time, a random one among them is chosen. If none of the operations become ready
+ /// before the deadline, an error is returned.
+ ///
+ /// An operation is considered to be ready if it doesn't have to block. Note that it is ready
+ /// even when it will simply return an error because the channel is disconnected.
+ ///
+ /// Note that this method might return with success spuriously, so it's a good idea to double
+ /// check if the operation is really ready.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::{Duration, Instant};
+ /// use crossbeam_channel::{unbounded, Select};
+ ///
+ /// let deadline = Instant::now() + Duration::from_millis(500);
+ ///
+ /// let (s1, r1) = unbounded();
+ /// let (s2, r2) = unbounded();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_secs(1));
+ /// s1.send(10).unwrap();
+ /// });
+ /// thread::spawn(move || s2.send(20).unwrap());
+ ///
+ /// let mut sel = Select::new();
+ /// let oper1 = sel.recv(&r1);
+ /// let oper2 = sel.recv(&r2);
+ ///
+ /// // The second operation will be selected because it becomes ready first.
+ /// match sel.ready_deadline(deadline) {
+ /// Err(_) => panic!("should not have timed out"),
+ /// Ok(i) if i == oper1 => assert_eq!(r1.try_recv(), Ok(10)),
+ /// Ok(i) if i == oper2 => assert_eq!(r2.try_recv(), Ok(20)),
+ /// Ok(_) => unreachable!(),
+ /// }
+ /// ```
+ pub fn ready_deadline(&mut self, deadline: Instant) -> Result<usize, ReadyTimeoutError> {
+ match run_ready(&mut self.handles, Timeout::At(deadline)) {
+ None => Err(ReadyTimeoutError),
+ Some(index) => Ok(index),
+ }
+ }
+}
+
+impl<'a> Clone for Select<'a> {
+ fn clone(&self) -> Select<'a> {
+ Select {
+ handles: self.handles.clone(),
+ next_index: self.next_index,
+ }
+ }
+}
+
+impl<'a> Default for Select<'a> {
+ fn default() -> Select<'a> {
+ Select::new()
+ }
+}
+
+impl fmt::Debug for Select<'_> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.pad("Select { .. }")
+ }
+}
+
+/// A selected operation that needs to be completed.
+///
+/// To complete the operation, call [`send`] or [`recv`].
+///
+/// # Panics
+///
+/// Forgetting to complete the operation is an error and might lead to deadlocks. If a
+/// `SelectedOperation` is dropped without completion, a panic occurs.
+///
+/// [`send`]: SelectedOperation::send
+/// [`recv`]: SelectedOperation::recv
+#[must_use]
+pub struct SelectedOperation<'a> {
+ /// Token needed to complete the operation.
+ token: Token,
+
+ /// The index of the selected operation.
+ index: usize,
+
+ /// The address of the selected `Sender` or `Receiver`.
+ ptr: *const u8,
+
+ /// Indicates that `Sender`s and `Receiver`s are borrowed.
+ _marker: PhantomData<&'a ()>,
+}
+
+impl SelectedOperation<'_> {
+ /// Returns the index of the selected operation.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::{bounded, Select};
+ ///
+ /// let (s1, r1) = bounded::<()>(0);
+ /// let (s2, r2) = bounded::<()>(0);
+ /// let (s3, r3) = bounded::<()>(1);
+ ///
+ /// let mut sel = Select::new();
+ /// let oper1 = sel.send(&s1);
+ /// let oper2 = sel.recv(&r2);
+ /// let oper3 = sel.send(&s3);
+ ///
+ /// // Only the last operation is ready.
+ /// let oper = sel.select();
+ /// assert_eq!(oper.index(), 2);
+ /// assert_eq!(oper.index(), oper3);
+ ///
+ /// // Complete the operation.
+ /// oper.send(&s3, ()).unwrap();
+ /// ```
+ pub fn index(&self) -> usize {
+ self.index
+ }
+
+ /// Completes the send operation.
+ ///
+ /// The passed [`Sender`] reference must be the same one that was used in [`Select::send`]
+ /// when the operation was added.
+ ///
+ /// # Panics
+ ///
+ /// Panics if an incorrect [`Sender`] reference is passed.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::{bounded, Select, SendError};
+ ///
+ /// let (s, r) = bounded::<i32>(0);
+ /// drop(r);
+ ///
+ /// let mut sel = Select::new();
+ /// let oper1 = sel.send(&s);
+ ///
+ /// let oper = sel.select();
+ /// assert_eq!(oper.index(), oper1);
+ /// assert_eq!(oper.send(&s, 10), Err(SendError(10)));
+ /// ```
+ pub fn send<T>(mut self, s: &Sender<T>, msg: T) -> Result<(), SendError<T>> {
+ assert!(
+ s as *const Sender<T> as *const u8 == self.ptr,
+ "passed a sender that wasn't selected",
+ );
+ let res = unsafe { channel::write(s, &mut self.token, msg) };
+ mem::forget(self);
+ res.map_err(SendError)
+ }
+
+ /// Completes the receive operation.
+ ///
+ /// The passed [`Receiver`] reference must be the same one that was used in [`Select::recv`]
+ /// when the operation was added.
+ ///
+ /// # Panics
+ ///
+ /// Panics if an incorrect [`Receiver`] reference is passed.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_channel::{bounded, Select, RecvError};
+ ///
+ /// let (s, r) = bounded::<i32>(0);
+ /// drop(s);
+ ///
+ /// let mut sel = Select::new();
+ /// let oper1 = sel.recv(&r);
+ ///
+ /// let oper = sel.select();
+ /// assert_eq!(oper.index(), oper1);
+ /// assert_eq!(oper.recv(&r), Err(RecvError));
+ /// ```
+ pub fn recv<T>(mut self, r: &Receiver<T>) -> Result<T, RecvError> {
+ assert!(
+ r as *const Receiver<T> as *const u8 == self.ptr,
+ "passed a receiver that wasn't selected",
+ );
+ let res = unsafe { channel::read(r, &mut self.token) };
+ mem::forget(self);
+ res.map_err(|_| RecvError)
+ }
+}
+
+impl fmt::Debug for SelectedOperation<'_> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.pad("SelectedOperation { .. }")
+ }
+}
+
+impl Drop for SelectedOperation<'_> {
+ fn drop(&mut self) {
+ panic!("dropped `SelectedOperation` without completing the operation");
+ }
+}
diff --git a/src/select_macro.rs b/src/select_macro.rs
new file mode 100644
index 0000000..f8b247e
--- /dev/null
+++ b/src/select_macro.rs
@@ -0,0 +1,1166 @@
+//! The `select!` macro.
+
+/// A helper macro for `select!` to hide the long list of macro patterns from the documentation.
+///
+/// The macro consists of two stages:
+/// 1. Parsing
+/// 2. Code generation
+///
+/// The parsing stage consists of these subparts:
+/// 1. `@list`: Turns a list of tokens into a list of cases.
+/// 2. `@list_errorN`: Diagnoses the syntax error.
+/// 3. `@case`: Parses a single case and verifies its argument list.
+///
+/// The codegen stage consists of these subparts:
+/// 1. `@init`: Attempts to optimize `select!` away and initializes the list of handles.
+/// 1. `@count`: Counts the listed cases.
+/// 3. `@add`: Adds send/receive operations to the list of handles and starts selection.
+/// 4. `@complete`: Completes the selected send/receive operation.
+///
+/// If the parsing stage encounters a syntax error or the codegen stage ends up with too many
+/// cases to process, the macro fails with a compile-time error.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! crossbeam_channel_internal {
+ // The list is empty. Now check the arguments of each processed case.
+ (@list
+ ()
+ ($($head:tt)*)
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @case
+ ($($head)*)
+ ()
+ ()
+ )
+ };
+ // If necessary, insert an empty argument list after `default`.
+ (@list
+ (default => $($tail:tt)*)
+ ($($head:tt)*)
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @list
+ (default() => $($tail)*)
+ ($($head)*)
+ )
+ };
+ // But print an error if `default` is followed by a `->`.
+ (@list
+ (default -> $($tail:tt)*)
+ ($($head:tt)*)
+ ) => {
+ compile_error!(
+ "expected `=>` after `default` case, found `->`"
+ )
+ };
+ // Print an error if there's an `->` after the argument list in the default case.
+ (@list
+ (default $args:tt -> $($tail:tt)*)
+ ($($head:tt)*)
+ ) => {
+ compile_error!(
+ "expected `=>` after `default` case, found `->`"
+ )
+ };
+ // Print an error if there is a missing result in a recv case.
+ (@list
+ (recv($($args:tt)*) => $($tail:tt)*)
+ ($($head:tt)*)
+ ) => {
+ compile_error!(
+ "expected `->` after `recv` case, found `=>`"
+ )
+ };
+ // Print an error if there is a missing result in a send case.
+ (@list
+ (send($($args:tt)*) => $($tail:tt)*)
+ ($($head:tt)*)
+ ) => {
+ compile_error!(
+ "expected `->` after `send` operation, found `=>`"
+ )
+ };
+ // Make sure the arrow and the result are not repeated.
+ (@list
+ ($case:ident $args:tt -> $res:tt -> $($tail:tt)*)
+ ($($head:tt)*)
+ ) => {
+ compile_error!("expected `=>`, found `->`")
+ };
+ // Print an error if there is a semicolon after the block.
+ (@list
+ ($case:ident $args:tt $(-> $res:pat)* => $body:block; $($tail:tt)*)
+ ($($head:tt)*)
+ ) => {
+ compile_error!(
+ "did you mean to put a comma instead of the semicolon after `}`?"
+ )
+ };
+ // The first case is separated by a comma.
+ (@list
+ ($case:ident ($($args:tt)*) $(-> $res:pat)* => $body:expr, $($tail:tt)*)
+ ($($head:tt)*)
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @list
+ ($($tail)*)
+ ($($head)* $case ($($args)*) $(-> $res)* => { $body },)
+ )
+ };
+ // Don't require a comma after the case if it has a proper block.
+ (@list
+ ($case:ident ($($args:tt)*) $(-> $res:pat)* => $body:block $($tail:tt)*)
+ ($($head:tt)*)
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @list
+ ($($tail)*)
+ ($($head)* $case ($($args)*) $(-> $res)* => { $body },)
+ )
+ };
+ // Only one case remains.
+ (@list
+ ($case:ident ($($args:tt)*) $(-> $res:pat)* => $body:expr)
+ ($($head:tt)*)
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @list
+ ()
+ ($($head)* $case ($($args)*) $(-> $res)* => { $body },)
+ )
+ };
+ // Accept a trailing comma at the end of the list.
+ (@list
+ ($case:ident ($($args:tt)*) $(-> $res:pat)* => $body:expr,)
+ ($($head:tt)*)
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @list
+ ()
+ ($($head)* $case ($($args)*) $(-> $res)* => { $body },)
+ )
+ };
+ // Diagnose and print an error.
+ (@list
+ ($($tail:tt)*)
+ ($($head:tt)*)
+ ) => {
+ $crate::crossbeam_channel_internal!(@list_error1 $($tail)*)
+ };
+ // Stage 1: check the case type.
+ (@list_error1 recv $($tail:tt)*) => {
+ $crate::crossbeam_channel_internal!(@list_error2 recv $($tail)*)
+ };
+ (@list_error1 send $($tail:tt)*) => {
+ $crate::crossbeam_channel_internal!(@list_error2 send $($tail)*)
+ };
+ (@list_error1 default $($tail:tt)*) => {
+ $crate::crossbeam_channel_internal!(@list_error2 default $($tail)*)
+ };
+ (@list_error1 $t:tt $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "expected one of `recv`, `send`, or `default`, found `",
+ stringify!($t),
+ "`",
+ )
+ )
+ };
+ (@list_error1 $($tail:tt)*) => {
+ $crate::crossbeam_channel_internal!(@list_error2 $($tail)*);
+ };
+ // Stage 2: check the argument list.
+ (@list_error2 $case:ident) => {
+ compile_error!(
+ concat!(
+ "missing argument list after `",
+ stringify!($case),
+ "`",
+ )
+ )
+ };
+ (@list_error2 $case:ident => $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "missing argument list after `",
+ stringify!($case),
+ "`",
+ )
+ )
+ };
+ (@list_error2 $($tail:tt)*) => {
+ $crate::crossbeam_channel_internal!(@list_error3 $($tail)*)
+ };
+ // Stage 3: check the `=>` and what comes after it.
+ (@list_error3 $case:ident($($args:tt)*) $(-> $r:pat)*) => {
+ compile_error!(
+ concat!(
+ "missing `=>` after `",
+ stringify!($case),
+ "` case",
+ )
+ )
+ };
+ (@list_error3 $case:ident($($args:tt)*) $(-> $r:pat)* =>) => {
+ compile_error!(
+ "expected expression after `=>`"
+ )
+ };
+ (@list_error3 $case:ident($($args:tt)*) $(-> $r:pat)* => $body:expr; $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "did you mean to put a comma instead of the semicolon after `",
+ stringify!($body),
+ "`?",
+ )
+ )
+ };
+ (@list_error3 $case:ident($($args:tt)*) $(-> $r:pat)* => recv($($a:tt)*) $($tail:tt)*) => {
+ compile_error!(
+ "expected an expression after `=>`"
+ )
+ };
+ (@list_error3 $case:ident($($args:tt)*) $(-> $r:pat)* => send($($a:tt)*) $($tail:tt)*) => {
+ compile_error!(
+ "expected an expression after `=>`"
+ )
+ };
+ (@list_error3 $case:ident($($args:tt)*) $(-> $r:pat)* => default($($a:tt)*) $($tail:tt)*) => {
+ compile_error!(
+ "expected an expression after `=>`"
+ )
+ };
+ (@list_error3 $case:ident($($args:tt)*) $(-> $r:pat)* => $f:ident($($a:tt)*) $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "did you mean to put a comma after `",
+ stringify!($f),
+ "(",
+ stringify!($($a)*),
+ ")`?",
+ )
+ )
+ };
+ (@list_error3 $case:ident($($args:tt)*) $(-> $r:pat)* => $f:ident!($($a:tt)*) $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "did you mean to put a comma after `",
+ stringify!($f),
+ "!(",
+ stringify!($($a)*),
+ ")`?",
+ )
+ )
+ };
+ (@list_error3 $case:ident($($args:tt)*) $(-> $r:pat)* => $f:ident![$($a:tt)*] $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "did you mean to put a comma after `",
+ stringify!($f),
+ "![",
+ stringify!($($a)*),
+ "]`?",
+ )
+ )
+ };
+ (@list_error3 $case:ident($($args:tt)*) $(-> $r:pat)* => $f:ident!{$($a:tt)*} $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "did you mean to put a comma after `",
+ stringify!($f),
+ "!{",
+ stringify!($($a)*),
+ "}`?",
+ )
+ )
+ };
+ (@list_error3 $case:ident($($args:tt)*) $(-> $r:pat)* => $body:tt $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "did you mean to put a comma after `",
+ stringify!($body),
+ "`?",
+ )
+ )
+ };
+ (@list_error3 $case:ident($($args:tt)*) -> => $($tail:tt)*) => {
+ compile_error!("missing pattern after `->`")
+ };
+ (@list_error3 $case:ident($($args:tt)*) $t:tt $(-> $r:pat)* => $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "expected `->`, found `",
+ stringify!($t),
+ "`",
+ )
+ )
+ };
+ (@list_error3 $case:ident($($args:tt)*) -> $t:tt $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "expected a pattern, found `",
+ stringify!($t),
+ "`",
+ )
+ )
+ };
+ (@list_error3 recv($($args:tt)*) $t:tt $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "expected `->`, found `",
+ stringify!($t),
+ "`",
+ )
+ )
+ };
+ (@list_error3 send($($args:tt)*) $t:tt $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "expected `->`, found `",
+ stringify!($t),
+ "`",
+ )
+ )
+ };
+ (@list_error3 recv $args:tt $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "expected an argument list after `recv`, found `",
+ stringify!($args),
+ "`",
+ )
+ )
+ };
+ (@list_error3 send $args:tt $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "expected an argument list after `send`, found `",
+ stringify!($args),
+ "`",
+ )
+ )
+ };
+ (@list_error3 default $args:tt $($tail:tt)*) => {
+ compile_error!(
+ concat!(
+ "expected an argument list or `=>` after `default`, found `",
+ stringify!($args),
+ "`",
+ )
+ )
+ };
+ (@list_error3 $($tail:tt)*) => {
+ $crate::crossbeam_channel_internal!(@list_error4 $($tail)*)
+ };
+ // Stage 4: fail with a generic error message.
+ (@list_error4 $($tail:tt)*) => {
+ compile_error!("invalid syntax")
+ };
+
+ // Success! All cases were parsed.
+ (@case
+ ()
+ $cases:tt
+ $default:tt
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @init
+ $cases
+ $default
+ )
+ };
+
+ // Check the format of a recv case.
+ (@case
+ (recv($r:expr) -> $res:pat => $body:tt, $($tail:tt)*)
+ ($($cases:tt)*)
+ $default:tt
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @case
+ ($($tail)*)
+ ($($cases)* recv($r) -> $res => $body,)
+ $default
+ )
+ };
+ // Allow trailing comma...
+ (@case
+ (recv($r:expr,) -> $res:pat => $body:tt, $($tail:tt)*)
+ ($($cases:tt)*)
+ $default:tt
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @case
+ ($($tail)*)
+ ($($cases)* recv($r) -> $res => $body,)
+ $default
+ )
+ };
+ // Print an error if the argument list is invalid.
+ (@case
+ (recv($($args:tt)*) -> $res:pat => $body:tt, $($tail:tt)*)
+ ($($cases:tt)*)
+ $default:tt
+ ) => {
+ compile_error!(
+ concat!(
+ "invalid argument list in `recv(",
+ stringify!($($args)*),
+ ")`",
+ )
+ )
+ };
+ // Print an error if there is no argument list.
+ (@case
+ (recv $t:tt $($tail:tt)*)
+ ($($cases:tt)*)
+ $default:tt
+ ) => {
+ compile_error!(
+ concat!(
+ "expected an argument list after `recv`, found `",
+ stringify!($t),
+ "`",
+ )
+ )
+ };
+
+ // Check the format of a send case.
+ (@case
+ (send($s:expr, $m:expr) -> $res:pat => $body:tt, $($tail:tt)*)
+ ($($cases:tt)*)
+ $default:tt
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @case
+ ($($tail)*)
+ ($($cases)* send($s, $m) -> $res => $body,)
+ $default
+ )
+ };
+ // Allow trailing comma...
+ (@case
+ (send($s:expr, $m:expr,) -> $res:pat => $body:tt, $($tail:tt)*)
+ ($($cases:tt)*)
+ $default:tt
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @case
+ ($($tail)*)
+ ($($cases)* send($s, $m) -> $res => $body,)
+ $default
+ )
+ };
+ // Print an error if the argument list is invalid.
+ (@case
+ (send($($args:tt)*) -> $res:pat => $body:tt, $($tail:tt)*)
+ ($($cases:tt)*)
+ $default:tt
+ ) => {
+ compile_error!(
+ concat!(
+ "invalid argument list in `send(",
+ stringify!($($args)*),
+ ")`",
+ )
+ )
+ };
+ // Print an error if there is no argument list.
+ (@case
+ (send $t:tt $($tail:tt)*)
+ ($($cases:tt)*)
+ $default:tt
+ ) => {
+ compile_error!(
+ concat!(
+ "expected an argument list after `send`, found `",
+ stringify!($t),
+ "`",
+ )
+ )
+ };
+
+ // Check the format of a default case.
+ (@case
+ (default() => $body:tt, $($tail:tt)*)
+ $cases:tt
+ ()
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @case
+ ($($tail)*)
+ $cases
+ (default() => $body,)
+ )
+ };
+ // Check the format of a default case with timeout.
+ (@case
+ (default($timeout:expr) => $body:tt, $($tail:tt)*)
+ $cases:tt
+ ()
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @case
+ ($($tail)*)
+ $cases
+ (default($timeout) => $body,)
+ )
+ };
+ // Allow trailing comma...
+ (@case
+ (default($timeout:expr,) => $body:tt, $($tail:tt)*)
+ $cases:tt
+ ()
+ ) => {
+ $crate::crossbeam_channel_internal!(
+ @case
+ ($($tail)*)
+ $cases
+ (default($timeout) => $body,)
+ )
+ };
+ // Check for duplicate default cases...
+ (@case
+ (default $($tail:tt)*)
+ $cases:tt
+ ($($def:tt)+)
+ ) => {
+ compile_error!(
+ "there can be only one `default` case in a `select!` block"
+ )
+ };
+ // Print an error if the argument list is invalid.
+ (@case
+ (default($($args:tt)*) => $body:tt, $($tail:tt)*)
+ $cases:tt
+ $default:tt
+ ) => {
+ compile_error!(
+ concat!(
+ "invalid argument list in `default(",
+ stringify!($($args)*),
+ ")`",
+ )
+ )
+ };
+ // Print an error if there is an unexpected token after `default`.
+ (@case
+ (default $t:tt $($tail:tt)*)
+ $cases:tt
+ $default:tt
+ ) => {
+ compile_error!(
+ concat!(
+ "expected an argument list or `=>` after `default`, found `",
+ stringify!($t),
+ "`",
+ )
+ )
+ };
+
+ // The case was not consumed, therefore it must be invalid.
+ (@case
+ ($case:ident $($tail:tt)*)
+ $cases:tt
+ $default:tt
+ ) => {
+ compile_error!(
+ concat!(
+ "expected one of `recv`, `send`, or `default`, found `",
+ stringify!($case),
+ "`",
+ )
+ )
+ };
+
+ // Optimize `select!` into `try_recv()`.
+ (@init
+ (recv($r:expr) -> $res:pat => $recv_body:tt,)
+ (default() => $default_body:tt,)
+ ) => {{
+ match $r {
+ ref _r => {
+ let _r: &$crate::Receiver<_> = _r;
+ match _r.try_recv() {
+ ::std::result::Result::Err($crate::TryRecvError::Empty) => {
+ $default_body
+ }
+ _res => {
+ let _res = _res.map_err(|_| $crate::RecvError);
+ let $res = _res;
+ $recv_body
+ }
+ }
+ }
+ }
+ }};
+ // Optimize `select!` into `recv()`.
+ (@init
+ (recv($r:expr) -> $res:pat => $body:tt,)
+ ()
+ ) => {{
+ match $r {
+ ref _r => {
+ let _r: &$crate::Receiver<_> = _r;
+ let _res = _r.recv();
+ let $res = _res;
+ $body
+ }
+ }
+ }};
+ // Optimize `select!` into `recv_timeout()`.
+ (@init
+ (recv($r:expr) -> $res:pat => $recv_body:tt,)
+ (default($timeout:expr) => $default_body:tt,)
+ ) => {{
+ match $r {
+ ref _r => {
+ let _r: &$crate::Receiver<_> = _r;
+ match _r.recv_timeout($timeout) {
+ ::std::result::Result::Err($crate::RecvTimeoutError::Timeout) => {
+ $default_body
+ }
+ _res => {
+ let _res = _res.map_err(|_| $crate::RecvError);
+ let $res = _res;
+ $recv_body
+ }
+ }
+ }
+ }
+ }};
+
+ // // Optimize the non-blocking case with two receive operations.
+ // (@init
+ // (recv($r1:expr) -> $res1:pat => $recv_body1:tt,)
+ // (recv($r2:expr) -> $res2:pat => $recv_body2:tt,)
+ // (default() => $default_body:tt,)
+ // ) => {{
+ // match $r1 {
+ // ref _r1 => {
+ // let _r1: &$crate::Receiver<_> = _r1;
+ //
+ // match $r2 {
+ // ref _r2 => {
+ // let _r2: &$crate::Receiver<_> = _r2;
+ //
+ // // TODO(stjepang): Implement this optimization.
+ // }
+ // }
+ // }
+ // }
+ // }};
+ // // Optimize the blocking case with two receive operations.
+ // (@init
+ // (recv($r1:expr) -> $res1:pat => $body1:tt,)
+ // (recv($r2:expr) -> $res2:pat => $body2:tt,)
+ // ()
+ // ) => {{
+ // match $r1 {
+ // ref _r1 => {
+ // let _r1: &$crate::Receiver<_> = _r1;
+ //
+ // match $r2 {
+ // ref _r2 => {
+ // let _r2: &$crate::Receiver<_> = _r2;
+ //
+ // // TODO(stjepang): Implement this optimization.
+ // }
+ // }
+ // }
+ // }
+ // }};
+ // // Optimize the case with two receive operations and a timeout.
+ // (@init
+ // (recv($r1:expr) -> $res1:pat => $recv_body1:tt,)
+ // (recv($r2:expr) -> $res2:pat => $recv_body2:tt,)
+ // (default($timeout:expr) => $default_body:tt,)
+ // ) => {{
+ // match $r1 {
+ // ref _r1 => {
+ // let _r1: &$crate::Receiver<_> = _r1;
+ //
+ // match $r2 {
+ // ref _r2 => {
+ // let _r2: &$crate::Receiver<_> = _r2;
+ //
+ // // TODO(stjepang): Implement this optimization.
+ // }
+ // }
+ // }
+ // }
+ // }};
+
+ // // Optimize `select!` into `try_send()`.
+ // (@init
+ // (send($s:expr, $m:expr) -> $res:pat => $send_body:tt,)
+ // (default() => $default_body:tt,)
+ // ) => {{
+ // match $s {
+ // ref _s => {
+ // let _s: &$crate::Sender<_> = _s;
+ // // TODO(stjepang): Implement this optimization.
+ // }
+ // }
+ // }};
+ // // Optimize `select!` into `send()`.
+ // (@init
+ // (send($s:expr, $m:expr) -> $res:pat => $body:tt,)
+ // ()
+ // ) => {{
+ // match $s {
+ // ref _s => {
+ // let _s: &$crate::Sender<_> = _s;
+ // // TODO(stjepang): Implement this optimization.
+ // }
+ // }
+ // }};
+ // // Optimize `select!` into `send_timeout()`.
+ // (@init
+ // (send($s:expr, $m:expr) -> $res:pat => $body:tt,)
+ // (default($timeout:expr) => $body:tt,)
+ // ) => {{
+ // match $s {
+ // ref _s => {
+ // let _s: &$crate::Sender<_> = _s;
+ // // TODO(stjepang): Implement this optimization.
+ // }
+ // }
+ // }};
+
+ // Create the list of handles and add operations to it.
+ (@init
+ ($($cases:tt)*)
+ $default:tt
+ ) => {{
+ const _LEN: usize = $crate::crossbeam_channel_internal!(@count ($($cases)*));
+ let _handle: &$crate::internal::SelectHandle = &$crate::never::<()>();
+
+ #[allow(unused_mut)]
+ let mut _sel = [(_handle, 0, ::std::ptr::null()); _LEN];
+
+ $crate::crossbeam_channel_internal!(
+ @add
+ _sel
+ ($($cases)*)
+ $default
+ (
+ (0usize _oper0)
+ (1usize _oper1)
+ (2usize _oper2)
+ (3usize _oper3)
+ (4usize _oper4)
+ (5usize _oper5)
+ (6usize _oper6)
+ (7usize _oper7)
+ (8usize _oper8)
+ (9usize _oper9)
+ (10usize _oper10)
+ (11usize _oper11)
+ (12usize _oper12)
+ (13usize _oper13)
+ (14usize _oper14)
+ (15usize _oper15)
+ (16usize _oper16)
+ (17usize _oper17)
+ (18usize _oper18)
+ (19usize _oper19)
+ (20usize _oper20)
+ (21usize _oper21)
+ (22usize _oper22)
+ (23usize _oper23)
+ (24usize _oper24)
+ (25usize _oper25)
+ (26usize _oper26)
+ (27usize _oper27)
+ (28usize _oper28)
+ (29usize _oper29)
+ (30usize _oper30)
+ (31usize _oper31)
+ )
+ ()
+ )
+ }};
+
+ // Count the listed cases.
+ (@count ()) => {
+ 0
+ };
+ (@count ($oper:ident $args:tt -> $res:pat => $body:tt, $($cases:tt)*)) => {
+ 1 + $crate::crossbeam_channel_internal!(@count ($($cases)*))
+ };
+
+ // Run blocking selection.
+ (@add
+ $sel:ident
+ ()
+ ()
+ $labels:tt
+ $cases:tt
+ ) => {{
+ let _oper: $crate::SelectedOperation<'_> = {
+ let _oper = $crate::internal::select(&mut $sel);
+
+ // Erase the lifetime so that `sel` can be dropped early even without NLL.
+ unsafe { ::std::mem::transmute(_oper) }
+ };
+
+ $crate::crossbeam_channel_internal! {
+ @complete
+ $sel
+ _oper
+ $cases
+ }
+ }};
+ // Run non-blocking selection.
+ (@add
+ $sel:ident
+ ()
+ (default() => $body:tt,)
+ $labels:tt
+ $cases:tt
+ ) => {{
+ let _oper: ::std::option::Option<$crate::SelectedOperation<'_>> = {
+ let _oper = $crate::internal::try_select(&mut $sel);
+
+ // Erase the lifetime so that `sel` can be dropped early even without NLL.
+ unsafe { ::std::mem::transmute(_oper) }
+ };
+
+ match _oper {
+ None => {
+ { $sel };
+ $body
+ }
+ Some(_oper) => {
+ $crate::crossbeam_channel_internal! {
+ @complete
+ $sel
+ _oper
+ $cases
+ }
+ }
+ }
+ }};
+ // Run selection with a timeout.
+ (@add
+ $sel:ident
+ ()
+ (default($timeout:expr) => $body:tt,)
+ $labels:tt
+ $cases:tt
+ ) => {{
+ let _oper: ::std::option::Option<$crate::SelectedOperation<'_>> = {
+ let _oper = $crate::internal::select_timeout(&mut $sel, $timeout);
+
+ // Erase the lifetime so that `sel` can be dropped early even without NLL.
+ unsafe { ::std::mem::transmute(_oper) }
+ };
+
+ match _oper {
+ ::std::option::Option::None => {
+ { $sel };
+ $body
+ }
+ ::std::option::Option::Some(_oper) => {
+ $crate::crossbeam_channel_internal! {
+ @complete
+ $sel
+ _oper
+ $cases
+ }
+ }
+ }
+ }};
+ // Have we used up all labels?
+ (@add
+ $sel:ident
+ $input:tt
+ $default:tt
+ ()
+ $cases:tt
+ ) => {
+ compile_error!("too many operations in a `select!` block")
+ };
+ // Add a receive operation to `sel`.
+ (@add
+ $sel:ident
+ (recv($r:expr) -> $res:pat => $body:tt, $($tail:tt)*)
+ $default:tt
+ (($i:tt $var:ident) $($labels:tt)*)
+ ($($cases:tt)*)
+ ) => {{
+ match $r {
+ ref _r => {
+ let $var: &$crate::Receiver<_> = unsafe {
+ let _r: &$crate::Receiver<_> = _r;
+
+ // Erase the lifetime so that `sel` can be dropped early even without NLL.
+ unsafe fn unbind<'a, T>(x: &T) -> &'a T {
+ ::std::mem::transmute(x)
+ }
+ unbind(_r)
+ };
+ $sel[$i] = ($var, $i, $var as *const $crate::Receiver<_> as *const u8);
+
+ $crate::crossbeam_channel_internal!(
+ @add
+ $sel
+ ($($tail)*)
+ $default
+ ($($labels)*)
+ ($($cases)* [$i] recv($var) -> $res => $body,)
+ )
+ }
+ }
+ }};
+ // Add a send operation to `sel`.
+ (@add
+ $sel:ident
+ (send($s:expr, $m:expr) -> $res:pat => $body:tt, $($tail:tt)*)
+ $default:tt
+ (($i:tt $var:ident) $($labels:tt)*)
+ ($($cases:tt)*)
+ ) => {{
+ match $s {
+ ref _s => {
+ let $var: &$crate::Sender<_> = unsafe {
+ let _s: &$crate::Sender<_> = _s;
+
+ // Erase the lifetime so that `sel` can be dropped early even without NLL.
+ unsafe fn unbind<'a, T>(x: &T) -> &'a T {
+ ::std::mem::transmute(x)
+ }
+ unbind(_s)
+ };
+ $sel[$i] = ($var, $i, $var as *const $crate::Sender<_> as *const u8);
+
+ $crate::crossbeam_channel_internal!(
+ @add
+ $sel
+ ($($tail)*)
+ $default
+ ($($labels)*)
+ ($($cases)* [$i] send($var, $m) -> $res => $body,)
+ )
+ }
+ }
+ }};
+
+ // Complete a receive operation.
+ (@complete
+ $sel:ident
+ $oper:ident
+ ([$i:tt] recv($r:ident) -> $res:pat => $body:tt, $($tail:tt)*)
+ ) => {{
+ if $oper.index() == $i {
+ let _res = $oper.recv($r);
+ { $sel };
+
+ let $res = _res;
+ $body
+ } else {
+ $crate::crossbeam_channel_internal! {
+ @complete
+ $sel
+ $oper
+ ($($tail)*)
+ }
+ }
+ }};
+ // Complete a send operation.
+ (@complete
+ $sel:ident
+ $oper:ident
+ ([$i:tt] send($s:ident, $m:expr) -> $res:pat => $body:tt, $($tail:tt)*)
+ ) => {{
+ if $oper.index() == $i {
+ let _res = $oper.send($s, $m);
+ { $sel };
+
+ let $res = _res;
+ $body
+ } else {
+ $crate::crossbeam_channel_internal! {
+ @complete
+ $sel
+ $oper
+ ($($tail)*)
+ }
+ }
+ }};
+ // Panic if we don't identify the selected case, but this should never happen.
+ (@complete
+ $sel:ident
+ $oper:ident
+ ()
+ ) => {{
+ unreachable!(
+ "internal error in crossbeam-channel: invalid case"
+ )
+ }};
+
+ // Catches a bug within this macro (should not happen).
+ (@$($tokens:tt)*) => {
+ compile_error!(
+ concat!(
+ "internal error in crossbeam-channel: ",
+ stringify!(@$($tokens)*),
+ )
+ )
+ };
+
+ // The entry points.
+ () => {
+ compile_error!("empty `select!` block")
+ };
+ ($($case:ident $(($($args:tt)*))* => $body:expr $(,)*)*) => {
+ $crate::crossbeam_channel_internal!(
+ @list
+ ($($case $(($($args)*))* => { $body },)*)
+ ()
+ )
+ };
+ ($($tokens:tt)*) => {
+ $crate::crossbeam_channel_internal!(
+ @list
+ ($($tokens)*)
+ ()
+ )
+ };
+}
+
+/// Selects from a set of channel operations.
+///
+/// This macro allows you to define a set of channel operations, wait until any one of them becomes
+/// ready, and finally execute it. If multiple operations are ready at the same time, a random one
+/// among them is selected.
+///
+/// It is also possible to define a `default` case that gets executed if none of the operations are
+/// ready, either right away or for a certain duration of time.
+///
+/// An operation is considered to be ready if it doesn't have to block. Note that it is ready even
+/// when it will simply return an error because the channel is disconnected.
+///
+/// The `select` macro is a convenience wrapper around [`Select`]. However, it cannot select over a
+/// dynamically created list of channel operations.
+///
+/// [`Select`]: super::Select
+///
+/// # Examples
+///
+/// Block until a send or a receive operation is selected:
+///
+/// ```
+/// use crossbeam_channel::{select, unbounded};
+///
+/// let (s1, r1) = unbounded();
+/// let (s2, r2) = unbounded();
+/// s1.send(10).unwrap();
+///
+/// // Since both operations are initially ready, a random one will be executed.
+/// select! {
+/// recv(r1) -> msg => assert_eq!(msg, Ok(10)),
+/// send(s2, 20) -> res => {
+/// assert_eq!(res, Ok(()));
+/// assert_eq!(r2.recv(), Ok(20));
+/// }
+/// }
+/// ```
+///
+/// Select from a set of operations without blocking:
+///
+/// ```
+/// use std::thread;
+/// use std::time::Duration;
+/// use crossbeam_channel::{select, unbounded};
+///
+/// let (s1, r1) = unbounded();
+/// let (s2, r2) = unbounded();
+///
+/// thread::spawn(move || {
+/// thread::sleep(Duration::from_secs(1));
+/// s1.send(10).unwrap();
+/// });
+/// thread::spawn(move || {
+/// thread::sleep(Duration::from_millis(500));
+/// s2.send(20).unwrap();
+/// });
+///
+/// // None of the operations are initially ready.
+/// select! {
+/// recv(r1) -> msg => panic!(),
+/// recv(r2) -> msg => panic!(),
+/// default => println!("not ready"),
+/// }
+/// ```
+///
+/// Select over a set of operations with a timeout:
+///
+/// ```
+/// use std::thread;
+/// use std::time::Duration;
+/// use crossbeam_channel::{select, unbounded};
+///
+/// let (s1, r1) = unbounded();
+/// let (s2, r2) = unbounded();
+///
+/// thread::spawn(move || {
+/// thread::sleep(Duration::from_secs(1));
+/// s1.send(10).unwrap();
+/// });
+/// thread::spawn(move || {
+/// thread::sleep(Duration::from_millis(500));
+/// s2.send(20).unwrap();
+/// });
+///
+/// // None of the two operations will become ready within 100 milliseconds.
+/// select! {
+/// recv(r1) -> msg => panic!(),
+/// recv(r2) -> msg => panic!(),
+/// default(Duration::from_millis(100)) => println!("timed out"),
+/// }
+/// ```
+///
+/// Optionally add a receive operation to `select!` using [`never`]:
+///
+/// ```
+/// use std::thread;
+/// use std::time::Duration;
+/// use crossbeam_channel::{select, never, unbounded};
+///
+/// let (s1, r1) = unbounded();
+/// let (s2, r2) = unbounded();
+///
+/// thread::spawn(move || {
+/// thread::sleep(Duration::from_secs(1));
+/// s1.send(10).unwrap();
+/// });
+/// thread::spawn(move || {
+/// thread::sleep(Duration::from_millis(500));
+/// s2.send(20).unwrap();
+/// });
+///
+/// // This receiver can be a `Some` or a `None`.
+/// let r2 = Some(&r2);
+///
+/// // None of the two operations will become ready within 100 milliseconds.
+/// select! {
+/// recv(r1) -> msg => panic!(),
+/// recv(r2.unwrap_or(&never())) -> msg => assert_eq!(msg, Ok(20)),
+/// }
+/// ```
+///
+/// To optionally add a timeout to `select!`, see the [example] for [`never`].
+///
+/// [`never`]: super::never
+/// [example]: super::never#examples
+#[macro_export]
+macro_rules! select {
+ ($($tokens:tt)*) => {
+ $crate::crossbeam_channel_internal!(
+ $($tokens)*
+ )
+ };
+}
diff --git a/src/utils.rs b/src/utils.rs
new file mode 100644
index 0000000..3fe171b
--- /dev/null
+++ b/src/utils.rs
@@ -0,0 +1,112 @@
+//! Miscellaneous utilities.
+
+use std::cell::{Cell, UnsafeCell};
+use std::num::Wrapping;
+use std::ops::{Deref, DerefMut};
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::thread;
+use std::time::{Duration, Instant};
+
+use crossbeam_utils::Backoff;
+
+/// Randomly shuffles a slice.
+pub fn shuffle<T>(v: &mut [T]) {
+ let len = v.len();
+ if len <= 1 {
+ return;
+ }
+
+ thread_local! {
+ static RNG: Cell<Wrapping<u32>> = Cell::new(Wrapping(1_406_868_647));
+ }
+
+ let _ = RNG.try_with(|rng| {
+ for i in 1..len {
+ // This is the 32-bit variant of Xorshift.
+ //
+ // Source: https://en.wikipedia.org/wiki/Xorshift
+ let mut x = rng.get();
+ x ^= x << 13;
+ x ^= x >> 17;
+ x ^= x << 5;
+ rng.set(x);
+
+ let x = x.0;
+ let n = i + 1;
+
+ // This is a fast alternative to `let j = x % n`.
+ //
+ // Author: Daniel Lemire
+ // Source: https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
+ let j = ((x as u64).wrapping_mul(n as u64) >> 32) as u32 as usize;
+
+ v.swap(i, j);
+ }
+ });
+}
+
+/// Sleeps until the deadline, or forever if the deadline isn't specified.
+pub fn sleep_until(deadline: Option<Instant>) {
+ loop {
+ match deadline {
+ None => thread::sleep(Duration::from_secs(1000)),
+ Some(d) => {
+ let now = Instant::now();
+ if now >= d {
+ break;
+ }
+ thread::sleep(d - now);
+ }
+ }
+ }
+}
+
+/// A simple spinlock.
+pub struct Spinlock<T> {
+ flag: AtomicBool,
+ value: UnsafeCell<T>,
+}
+
+impl<T> Spinlock<T> {
+ /// Returns a new spinlock initialized with `value`.
+ pub fn new(value: T) -> Spinlock<T> {
+ Spinlock {
+ flag: AtomicBool::new(false),
+ value: UnsafeCell::new(value),
+ }
+ }
+
+ /// Locks the spinlock.
+ pub fn lock(&self) -> SpinlockGuard<'_, T> {
+ let backoff = Backoff::new();
+ while self.flag.swap(true, Ordering::Acquire) {
+ backoff.snooze();
+ }
+ SpinlockGuard { parent: self }
+ }
+}
+
+/// A guard holding a spinlock locked.
+pub struct SpinlockGuard<'a, T> {
+ parent: &'a Spinlock<T>,
+}
+
+impl<T> Drop for SpinlockGuard<'_, T> {
+ fn drop(&mut self) {
+ self.parent.flag.store(false, Ordering::Release);
+ }
+}
+
+impl<T> Deref for SpinlockGuard<'_, T> {
+ type Target = T;
+
+ fn deref(&self) -> &T {
+ unsafe { &*self.parent.value.get() }
+ }
+}
+
+impl<T> DerefMut for SpinlockGuard<'_, T> {
+ fn deref_mut(&mut self) -> &mut T {
+ unsafe { &mut *self.parent.value.get() }
+ }
+}
diff --git a/src/waker.rs b/src/waker.rs
new file mode 100644
index 0000000..3d0af26
--- /dev/null
+++ b/src/waker.rs
@@ -0,0 +1,287 @@
+//! Waking mechanism for threads blocked on channel operations.
+
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::thread::{self, ThreadId};
+
+use crate::context::Context;
+use crate::select::{Operation, Selected};
+use crate::utils::Spinlock;
+
+/// Represents a thread blocked on a specific channel operation.
+pub struct Entry {
+ /// The operation.
+ pub oper: Operation,
+
+ /// Optional packet.
+ pub packet: usize,
+
+ /// Context associated with the thread owning this operation.
+ pub cx: Context,
+}
+
+/// A queue of threads blocked on channel operations.
+///
+/// This data structure is used by threads to register blocking operations and get woken up once
+/// an operation becomes ready.
+pub struct Waker {
+ /// A list of select operations.
+ selectors: Vec<Entry>,
+
+ /// A list of operations waiting to be ready.
+ observers: Vec<Entry>,
+}
+
+impl Waker {
+ /// Creates a new `Waker`.
+ #[inline]
+ pub fn new() -> Self {
+ Waker {
+ selectors: Vec::new(),
+ observers: Vec::new(),
+ }
+ }
+
+ /// Registers a select operation.
+ #[inline]
+ pub fn register(&mut self, oper: Operation, cx: &Context) {
+ self.register_with_packet(oper, 0, cx);
+ }
+
+ /// Registers a select operation and a packet.
+ #[inline]
+ pub fn register_with_packet(&mut self, oper: Operation, packet: usize, cx: &Context) {
+ self.selectors.push(Entry {
+ oper,
+ packet,
+ cx: cx.clone(),
+ });
+ }
+
+ /// Unregisters a select operation.
+ #[inline]
+ pub fn unregister(&mut self, oper: Operation) -> Option<Entry> {
+ if let Some((i, _)) = self
+ .selectors
+ .iter()
+ .enumerate()
+ .find(|&(_, entry)| entry.oper == oper)
+ {
+ let entry = self.selectors.remove(i);
+ Some(entry)
+ } else {
+ None
+ }
+ }
+
+ /// Attempts to find another thread's entry, select the operation, and wake it up.
+ #[inline]
+ pub fn try_select(&mut self) -> Option<Entry> {
+ let mut entry = None;
+
+ if !self.selectors.is_empty() {
+ let thread_id = current_thread_id();
+
+ for i in 0..self.selectors.len() {
+ // Does the entry belong to a different thread?
+ if self.selectors[i].cx.thread_id() != thread_id {
+ // Try selecting this operation.
+ let sel = Selected::Operation(self.selectors[i].oper);
+ let res = self.selectors[i].cx.try_select(sel);
+
+ if res.is_ok() {
+ // Provide the packet.
+ self.selectors[i].cx.store_packet(self.selectors[i].packet);
+ // Wake the thread up.
+ self.selectors[i].cx.unpark();
+
+ // Remove the entry from the queue to keep it clean and improve
+ // performance.
+ entry = Some(self.selectors.remove(i));
+ break;
+ }
+ }
+ }
+ }
+
+ entry
+ }
+
+ /// Returns `true` if there is an entry which can be selected by the current thread.
+ #[inline]
+ pub fn can_select(&self) -> bool {
+ if self.selectors.is_empty() {
+ false
+ } else {
+ let thread_id = current_thread_id();
+
+ self.selectors.iter().any(|entry| {
+ entry.cx.thread_id() != thread_id && entry.cx.selected() == Selected::Waiting
+ })
+ }
+ }
+
+ /// Registers an operation waiting to be ready.
+ #[inline]
+ pub fn watch(&mut self, oper: Operation, cx: &Context) {
+ self.observers.push(Entry {
+ oper,
+ packet: 0,
+ cx: cx.clone(),
+ });
+ }
+
+ /// Unregisters an operation waiting to be ready.
+ #[inline]
+ pub fn unwatch(&mut self, oper: Operation) {
+ self.observers.retain(|e| e.oper != oper);
+ }
+
+ /// Notifies all operations waiting to be ready.
+ #[inline]
+ pub fn notify(&mut self) {
+ for entry in self.observers.drain(..) {
+ if entry.cx.try_select(Selected::Operation(entry.oper)).is_ok() {
+ entry.cx.unpark();
+ }
+ }
+ }
+
+ /// Notifies all registered operations that the channel is disconnected.
+ #[inline]
+ pub fn disconnect(&mut self) {
+ for entry in self.selectors.iter() {
+ if entry.cx.try_select(Selected::Disconnected).is_ok() {
+ // Wake the thread up.
+ //
+ // Here we don't remove the entry from the queue. Registered threads must
+ // unregister from the waker by themselves. They might also want to recover the
+ // packet value and destroy it, if necessary.
+ entry.cx.unpark();
+ }
+ }
+
+ self.notify();
+ }
+}
+
+impl Drop for Waker {
+ #[inline]
+ fn drop(&mut self) {
+ debug_assert_eq!(self.selectors.len(), 0);
+ debug_assert_eq!(self.observers.len(), 0);
+ }
+}
+
+/// A waker that can be shared among threads without locking.
+///
+/// This is a simple wrapper around `Waker` that internally uses a mutex for synchronization.
+pub struct SyncWaker {
+ /// The inner `Waker`.
+ inner: Spinlock<Waker>,
+
+ /// `true` if the waker is empty.
+ is_empty: AtomicBool,
+}
+
+impl SyncWaker {
+ /// Creates a new `SyncWaker`.
+ #[inline]
+ pub fn new() -> Self {
+ SyncWaker {
+ inner: Spinlock::new(Waker::new()),
+ is_empty: AtomicBool::new(true),
+ }
+ }
+
+ /// Registers the current thread with an operation.
+ #[inline]
+ pub fn register(&self, oper: Operation, cx: &Context) {
+ let mut inner = self.inner.lock();
+ inner.register(oper, cx);
+ self.is_empty.store(
+ inner.selectors.is_empty() && inner.observers.is_empty(),
+ Ordering::SeqCst,
+ );
+ }
+
+ /// Unregisters an operation previously registered by the current thread.
+ #[inline]
+ pub fn unregister(&self, oper: Operation) -> Option<Entry> {
+ let mut inner = self.inner.lock();
+ let entry = inner.unregister(oper);
+ self.is_empty.store(
+ inner.selectors.is_empty() && inner.observers.is_empty(),
+ Ordering::SeqCst,
+ );
+ entry
+ }
+
+ /// Attempts to find one thread (not the current one), select its operation, and wake it up.
+ #[inline]
+ pub fn notify(&self) {
+ if !self.is_empty.load(Ordering::SeqCst) {
+ let mut inner = self.inner.lock();
+ if !self.is_empty.load(Ordering::SeqCst) {
+ inner.try_select();
+ inner.notify();
+ self.is_empty.store(
+ inner.selectors.is_empty() && inner.observers.is_empty(),
+ Ordering::SeqCst,
+ );
+ }
+ }
+ }
+
+ /// Registers an operation waiting to be ready.
+ #[inline]
+ pub fn watch(&self, oper: Operation, cx: &Context) {
+ let mut inner = self.inner.lock();
+ inner.watch(oper, cx);
+ self.is_empty.store(
+ inner.selectors.is_empty() && inner.observers.is_empty(),
+ Ordering::SeqCst,
+ );
+ }
+
+ /// Unregisters an operation waiting to be ready.
+ #[inline]
+ pub fn unwatch(&self, oper: Operation) {
+ let mut inner = self.inner.lock();
+ inner.unwatch(oper);
+ self.is_empty.store(
+ inner.selectors.is_empty() && inner.observers.is_empty(),
+ Ordering::SeqCst,
+ );
+ }
+
+ /// Notifies all threads that the channel is disconnected.
+ #[inline]
+ pub fn disconnect(&self) {
+ let mut inner = self.inner.lock();
+ inner.disconnect();
+ self.is_empty.store(
+ inner.selectors.is_empty() && inner.observers.is_empty(),
+ Ordering::SeqCst,
+ );
+ }
+}
+
+impl Drop for SyncWaker {
+ #[inline]
+ fn drop(&mut self) {
+ debug_assert_eq!(self.is_empty.load(Ordering::SeqCst), true);
+ }
+}
+
+/// Returns the id of the current thread.
+#[inline]
+fn current_thread_id() -> ThreadId {
+ thread_local! {
+ /// Cached thread-local id.
+ static THREAD_ID: ThreadId = thread::current().id();
+ }
+
+ THREAD_ID
+ .try_with(|id| *id)
+ .unwrap_or_else(|_| thread::current().id())
+}
