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+//! # Flume
+//!
+//! A blazingly fast multi-producer, multi-consumer channel.
+//!
+//! *"Do not communicate by sharing memory; instead, share memory by communicating."*
+//!
+//! ## Why Flume?
+//!
+//! - **Featureful**: Unbounded, bounded and rendezvous queues
+//! - **Fast**: Always faster than `std::sync::mpsc` and sometimes `crossbeam-channel`
+//! - **Safe**: No `unsafe` code anywhere in the codebase!
+//! - **Flexible**: `Sender` and `Receiver` both implement `Send + Sync + Clone`
+//! - **Familiar**: Drop-in replacement for `std::sync::mpsc`
+//! - **Capable**: Additional features like MPMC support and send timeouts/deadlines
+//! - **Simple**: Few dependencies, minimal codebase, fast to compile
+//! - **Asynchronous**: `async` support, including mix 'n match with sync code
+//! - **Ergonomic**: Powerful `select`-like interface
+//!
+//! ## Example
+//!
+//! ```
+//! let (tx, rx) = flume::unbounded();
+//!
+//! tx.send(42).unwrap();
+//! assert_eq!(rx.recv().unwrap(), 42);
+//! ```
+
+#![deny(missing_docs)]
+
+#[cfg(feature = "select")]
+pub mod select;
+#[cfg(feature = "async")]
+pub mod r#async;
+
+mod signal;
+
+// Reexports
+#[cfg(feature = "select")]
+pub use select::Selector;
+
+use std::{
+ collections::VecDeque,
+ sync::{Arc, atomic::{AtomicUsize, AtomicBool, Ordering}, Weak},
+ time::{Duration, Instant},
+ marker::PhantomData,
+ thread,
+ fmt,
+};
+
+#[cfg(feature = "spin")]
+use spin1::{Mutex as Spinlock, MutexGuard as SpinlockGuard};
+use crate::signal::{Signal, SyncSignal};
+
+/// An error that may be emitted when attempting to send a value into a channel on a sender when
+/// all receivers are dropped.
+#[derive(Copy, Clone, PartialEq, Eq)]
+pub struct SendError<T>(pub T);
+
+impl<T> SendError<T> {
+ /// Consume the error, yielding the message that failed to send.
+ pub fn into_inner(self) -> T { self.0 }
+}
+
+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 closed channel".fmt(f)
+ }
+}
+
+impl<T> std::error::Error for SendError<T> {}
+
+/// An error that may be emitted when attempting to send a value into a channel on a sender when
+/// the channel is full or all receivers are dropped.
+#[derive(Copy, Clone, PartialEq, Eq)]
+pub enum TrySendError<T> {
+ /// The channel the message is sent on has a finite capacity and was full when the send was attempted.
+ Full(T),
+ /// All channel receivers were dropped and so the message has nobody to receive it.
+ Disconnected(T),
+}
+
+impl<T> TrySendError<T> {
+ /// Consume the error, yielding the message that failed to send.
+ pub fn into_inner(self) -> T {
+ match self {
+ Self::Full(msg) | Self::Disconnected(msg) => msg,
+ }
+ }
+}
+
+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 closed channel".fmt(f),
+ }
+ }
+}
+
+impl<T> std::error::Error for TrySendError<T> {}
+
+impl<T> From<SendError<T>> for TrySendError<T> {
+ fn from(err: SendError<T>) -> Self {
+ match err {
+ SendError(item) => Self::Disconnected(item),
+ }
+ }
+}
+
+/// An error that may be emitted when sending a value into a channel on a sender with a timeout when
+/// the send operation times out or all receivers are dropped.
+#[derive(Copy, Clone, PartialEq, Eq)]
+pub enum SendTimeoutError<T> {
+ /// A timeout occurred when attempting to send the message.
+ Timeout(T),
+ /// All channel receivers were dropped and so the message has nobody to receive it.
+ Disconnected(T),
+}
+
+impl<T> SendTimeoutError<T> {
+ /// Consume the error, yielding the message that failed to send.
+ pub fn into_inner(self) -> T {
+ match self {
+ Self::Timeout(msg) | Self::Disconnected(msg) => msg,
+ }
+ }
+}
+
+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 sending on a full channel".fmt(f),
+ SendTimeoutError::Disconnected(..) => "sending on a closed channel".fmt(f),
+ }
+ }
+}
+
+impl<T> std::error::Error for SendTimeoutError<T> {}
+
+impl<T> From<SendError<T>> for SendTimeoutError<T> {
+ fn from(err: SendError<T>) -> Self {
+ match err {
+ SendError(item) => Self::Disconnected(item),
+ }
+ }
+}
+
+enum TrySendTimeoutError<T> {
+ Full(T),
+ Disconnected(T),
+ Timeout(T),
+}
+
+/// An error that may be emitted when attempting to wait for a value on a receiver when all senders
+/// are dropped and there are no more messages in the channel.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum RecvError {
+ /// All senders were dropped and no messages are waiting in the channel, so no further messages can be received.
+ Disconnected,
+}
+
+impl fmt::Display for RecvError {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ match self {
+ RecvError::Disconnected => "receiving on a closed channel".fmt(f),
+ }
+ }
+}
+
+impl std::error::Error for RecvError {}
+
+/// An error that may be emitted when attempting to fetch a value on a receiver when there are no
+/// messages in the channel. If there are no messages in the channel and all senders are dropped,
+/// then `TryRecvError::Disconnected` will be returned.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum TryRecvError {
+ /// The channel was empty when the receive was attempted.
+ Empty,
+ /// All senders were dropped and no messages are waiting in the channel, so no further messages can be received.
+ Disconnected,
+}
+
+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 => "channel is empty and closed".fmt(f),
+ }
+ }
+}
+
+impl std::error::Error for TryRecvError {}
+
+impl From<RecvError> for TryRecvError {
+ fn from(err: RecvError) -> Self {
+ match err {
+ RecvError::Disconnected => Self::Disconnected,
+ }
+ }
+}
+
+/// An error that may be emitted when attempting to wait for a value on a receiver with a timeout
+/// when the receive operation times out or all senders are dropped and there are no values left
+/// in the channel.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum RecvTimeoutError {
+ /// A timeout occurred when attempting to receive a message.
+ Timeout,
+ /// All senders were dropped and no messages are waiting in the channel, so no further messages can be received.
+ Disconnected,
+}
+
+impl fmt::Display for RecvTimeoutError {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ match self {
+ RecvTimeoutError::Timeout => "timed out waiting on a channel".fmt(f),
+ RecvTimeoutError::Disconnected => "channel is empty and closed".fmt(f),
+ }
+ }
+}
+
+impl std::error::Error for RecvTimeoutError {}
+
+impl From<RecvError> for RecvTimeoutError {
+ fn from(err: RecvError) -> Self {
+ match err {
+ RecvError::Disconnected => Self::Disconnected,
+ }
+ }
+}
+
+enum TryRecvTimeoutError {
+ Empty,
+ Timeout,
+ Disconnected,
+}
+
+// TODO: Investigate some sort of invalidation flag for timeouts
+#[cfg(feature = "spin")]
+struct Hook<T, S: ?Sized>(Option<Spinlock<Option<T>>>, S);
+
+#[cfg(not(feature = "spin"))]
+struct Hook<T, S: ?Sized>(Option<Mutex<Option<T>>>, S);
+
+#[cfg(feature = "spin")]
+impl<T, S: ?Sized + Signal> Hook<T, S> {
+ pub fn slot(msg: Option<T>, signal: S) -> Arc<Self>
+ where
+ S: Sized,
+ {
+ Arc::new(Self(Some(Spinlock::new(msg)), signal))
+ }
+
+ fn lock(&self) -> Option<SpinlockGuard<'_, Option<T>>> {
+ self.0.as_ref().map(|s| s.lock())
+ }
+}
+
+#[cfg(not(feature = "spin"))]
+impl<T, S: ?Sized + Signal> Hook<T, S> {
+ pub fn slot(msg: Option<T>, signal: S) -> Arc<Self>
+ where
+ S: Sized,
+ {
+ Arc::new(Self(Some(Mutex::new(msg)), signal))
+ }
+
+ fn lock(&self) -> Option<MutexGuard<'_, Option<T>>> {
+ self.0.as_ref().map(|s| s.lock().unwrap())
+ }
+}
+
+impl<T, S: ?Sized + Signal> Hook<T, S> {
+ pub fn fire_recv(&self) -> (T, &S) {
+ let msg = self.lock().unwrap().take().unwrap();
+ (msg, self.signal())
+ }
+
+ pub fn fire_send(&self, msg: T) -> (Option<T>, &S) {
+ let ret = match self.lock() {
+ Some(mut lock) => {
+ *lock = Some(msg);
+ None
+ }
+ None => Some(msg),
+ };
+ (ret, self.signal())
+ }
+
+ pub fn is_empty(&self) -> bool {
+ self.lock().map(|s| s.is_none()).unwrap_or(true)
+ }
+
+ pub fn try_take(&self) -> Option<T> {
+ self.lock().unwrap().take()
+ }
+
+ pub fn trigger(signal: S) -> Arc<Self>
+ where
+ S: Sized,
+ {
+ Arc::new(Self(None, signal))
+ }
+
+ pub fn signal(&self) -> &S {
+ &self.1
+ }
+
+ pub fn fire_nothing(&self) -> bool {
+ self.signal().fire()
+ }
+}
+
+impl<T> Hook<T, SyncSignal> {
+ pub fn wait_recv(&self, abort: &AtomicBool) -> Option<T> {
+ loop {
+ let disconnected = abort.load(Ordering::SeqCst); // Check disconnect *before* msg
+ let msg = self.lock().unwrap().take();
+ if let Some(msg) = msg {
+ break Some(msg);
+ } else if disconnected {
+ break None;
+ } else {
+ self.signal().wait()
+ }
+ }
+ }
+
+ // Err(true) if timeout
+ pub fn wait_deadline_recv(&self, abort: &AtomicBool, deadline: Instant) -> Result<T, bool> {
+ loop {
+ let disconnected = abort.load(Ordering::SeqCst); // Check disconnect *before* msg
+ let msg = self.lock().unwrap().take();
+ if let Some(msg) = msg {
+ break Ok(msg);
+ } else if disconnected {
+ break Err(false);
+ } else if let Some(dur) = deadline.checked_duration_since(Instant::now()) {
+ self.signal().wait_timeout(dur);
+ } else {
+ break Err(true);
+ }
+ }
+ }
+
+ pub fn wait_send(&self, abort: &AtomicBool) {
+ loop {
+ let disconnected = abort.load(Ordering::SeqCst); // Check disconnect *before* msg
+ if disconnected || self.lock().unwrap().is_none() {
+ break;
+ }
+
+ self.signal().wait();
+ }
+ }
+
+ // Err(true) if timeout
+ pub fn wait_deadline_send(&self, abort: &AtomicBool, deadline: Instant) -> Result<(), bool> {
+ loop {
+ let disconnected = abort.load(Ordering::SeqCst); // Check disconnect *before* msg
+ if self.lock().unwrap().is_none() {
+ break Ok(());
+ } else if disconnected {
+ break Err(false);
+ } else if let Some(dur) = deadline.checked_duration_since(Instant::now()) {
+ self.signal().wait_timeout(dur);
+ } else {
+ break Err(true);
+ }
+ }
+ }
+}
+
+#[cfg(feature = "spin")]
+#[inline]
+fn wait_lock<T>(lock: &Spinlock<T>) -> SpinlockGuard<T> {
+ let mut i = 4;
+ loop {
+ for _ in 0..10 {
+ if let Some(guard) = lock.try_lock() {
+ return guard;
+ }
+ thread::yield_now();
+ }
+ // Sleep for at most ~1 ms
+ thread::sleep(Duration::from_nanos(1 << i.min(20)));
+ i += 1;
+ }
+}
+
+#[cfg(not(feature = "spin"))]
+#[inline]
+fn wait_lock<'a, T>(lock: &'a Mutex<T>) -> MutexGuard<'a, T> {
+ lock.lock().unwrap()
+}
+
+#[cfg(not(feature = "spin"))]
+use std::sync::{Mutex, MutexGuard};
+
+#[cfg(feature = "spin")]
+type ChanLock<T> = Spinlock<T>;
+#[cfg(not(feature = "spin"))]
+type ChanLock<T> = Mutex<T>;
+
+
+type SignalVec<T> = VecDeque<Arc<Hook<T, dyn signal::Signal>>>;
+struct Chan<T> {
+ sending: Option<(usize, SignalVec<T>)>,
+ queue: VecDeque<T>,
+ waiting: SignalVec<T>,
+}
+
+impl<T> Chan<T> {
+ fn pull_pending(&mut self, pull_extra: bool) {
+ if let Some((cap, sending)) = &mut self.sending {
+ let effective_cap = *cap + pull_extra as usize;
+
+ while self.queue.len() < effective_cap {
+ if let Some(s) = sending.pop_front() {
+ let (msg, signal) = s.fire_recv();
+ signal.fire();
+ self.queue.push_back(msg);
+ } else {
+ break;
+ }
+ }
+ }
+ }
+
+ fn try_wake_receiver_if_pending(&mut self) {
+ if !self.queue.is_empty() {
+ while Some(false) == self.waiting.pop_front().map(|s| s.fire_nothing()) {}
+ }
+ }
+}
+
+struct Shared<T> {
+ chan: ChanLock<Chan<T>>,
+ disconnected: AtomicBool,
+ sender_count: AtomicUsize,
+ receiver_count: AtomicUsize,
+}
+
+impl<T> Shared<T> {
+ fn new(cap: Option<usize>) -> Self {
+ Self {
+ chan: ChanLock::new(Chan {
+ sending: cap.map(|cap| (cap, VecDeque::new())),
+ queue: VecDeque::new(),
+ waiting: VecDeque::new(),
+ }),
+ disconnected: AtomicBool::new(false),
+ sender_count: AtomicUsize::new(1),
+ receiver_count: AtomicUsize::new(1),
+ }
+ }
+
+ fn send<S: Signal, R: From<Result<(), TrySendTimeoutError<T>>>>(
+ &self,
+ msg: T,
+ should_block: bool,
+ make_signal: impl FnOnce(T) -> Arc<Hook<T, S>>,
+ do_block: impl FnOnce(Arc<Hook<T, S>>) -> R,
+ ) -> R {
+ let mut chan = wait_lock(&self.chan);
+
+ if self.is_disconnected() {
+ Err(TrySendTimeoutError::Disconnected(msg)).into()
+ } else if !chan.waiting.is_empty() {
+ let mut msg = Some(msg);
+
+ loop {
+ let slot = chan.waiting.pop_front();
+ match slot.as_ref().map(|r| r.fire_send(msg.take().unwrap())) {
+ // No more waiting receivers and msg in queue, so break out of the loop
+ None if msg.is_none() => break,
+ // No more waiting receivers, so add msg to queue and break out of the loop
+ None => {
+ chan.queue.push_back(msg.unwrap());
+ break;
+ }
+ Some((Some(m), signal)) => {
+ if signal.fire() {
+ // Was async and a stream, so didn't acquire the message. Wake another
+ // receiver, and do not yet push the message.
+ msg.replace(m);
+ continue;
+ } else {
+ // Was async and not a stream, so it did acquire the message. Push the
+ // message to the queue for it to be received.
+ chan.queue.push_back(m);
+ drop(chan);
+ break;
+ }
+ },
+ Some((None, signal)) => {
+ drop(chan);
+ signal.fire();
+ break; // Was sync, so it has acquired the message
+ },
+ }
+ }
+
+ Ok(()).into()
+ } else if chan.sending.as_ref().map(|(cap, _)| chan.queue.len() < *cap).unwrap_or(true) {
+ chan.queue.push_back(msg);
+ Ok(()).into()
+ } else if should_block { // Only bounded from here on
+ let hook = make_signal(msg);
+ chan.sending.as_mut().unwrap().1.push_back(hook.clone());
+ drop(chan);
+
+ do_block(hook)
+ } else {
+ Err(TrySendTimeoutError::Full(msg)).into()
+ }
+ }
+
+ fn send_sync(
+ &self,
+ msg: T,
+ block: Option<Option<Instant>>,
+ ) -> Result<(), TrySendTimeoutError<T>> {
+ self.send(
+ // msg
+ msg,
+ // should_block
+ block.is_some(),
+ // make_signal
+ |msg| Hook::slot(Some(msg), SyncSignal::default()),
+ // do_block
+ |hook| if let Some(deadline) = block.unwrap() {
+ hook.wait_deadline_send(&self.disconnected, deadline)
+ .or_else(|timed_out| {
+ if timed_out { // Remove our signal
+ let hook: Arc<Hook<T, dyn signal::Signal>> = hook.clone();
+ wait_lock(&self.chan).sending
+ .as_mut()
+ .unwrap().1
+ .retain(|s| s.signal().as_ptr() != hook.signal().as_ptr());
+ }
+ hook.try_take().map(|msg| if self.is_disconnected() {
+ Err(TrySendTimeoutError::Disconnected(msg))
+ } else {
+ Err(TrySendTimeoutError::Timeout(msg))
+ })
+ .unwrap_or(Ok(()))
+ })
+ } else {
+ hook.wait_send(&self.disconnected);
+
+ match hook.try_take() {
+ Some(msg) => Err(TrySendTimeoutError::Disconnected(msg)),
+ None => Ok(()),
+ }
+ },
+ )
+ }
+
+ fn recv<S: Signal, R: From<Result<T, TryRecvTimeoutError>>>(
+ &self,
+ should_block: bool,
+ make_signal: impl FnOnce() -> Arc<Hook<T, S>>,
+ do_block: impl FnOnce(Arc<Hook<T, S>>) -> R,
+ ) -> R {
+ let mut chan = wait_lock(&self.chan);
+ chan.pull_pending(true);
+
+ if let Some(msg) = chan.queue.pop_front() {
+ drop(chan);
+ Ok(msg).into()
+ } else if self.is_disconnected() {
+ drop(chan);
+ Err(TryRecvTimeoutError::Disconnected).into()
+ } else if should_block {
+ let hook = make_signal();
+ chan.waiting.push_back(hook.clone());
+ drop(chan);
+
+ do_block(hook)
+ } else {
+ drop(chan);
+ Err(TryRecvTimeoutError::Empty).into()
+ }
+ }
+
+ fn recv_sync(&self, block: Option<Option<Instant>>) -> Result<T, TryRecvTimeoutError> {
+ self.recv(
+ // should_block
+ block.is_some(),
+ // make_signal
+ || Hook::slot(None, SyncSignal::default()),
+ // do_block
+ |hook| if let Some(deadline) = block.unwrap() {
+ hook.wait_deadline_recv(&self.disconnected, deadline)
+ .or_else(|timed_out| {
+ if timed_out { // Remove our signal
+ let hook: Arc<Hook<T, dyn Signal>> = hook.clone();
+ wait_lock(&self.chan).waiting
+ .retain(|s| s.signal().as_ptr() != hook.signal().as_ptr());
+ }
+ match hook.try_take() {
+ Some(msg) => Ok(msg),
+ None => {
+ let disconnected = self.is_disconnected(); // Check disconnect *before* msg
+ if let Some(msg) = wait_lock(&self.chan).queue.pop_front() {
+ Ok(msg)
+ } else if disconnected {
+ Err(TryRecvTimeoutError::Disconnected)
+ } else {
+ Err(TryRecvTimeoutError::Timeout)
+ }
+ },
+ }
+ })
+ } else {
+ hook.wait_recv(&self.disconnected)
+ .or_else(|| wait_lock(&self.chan).queue.pop_front())
+ .ok_or(TryRecvTimeoutError::Disconnected)
+ },
+ )
+ }
+
+ /// Disconnect anything listening on this channel (this will not prevent receivers receiving
+ /// msgs that have already been sent)
+ fn disconnect_all(&self) {
+ self.disconnected.store(true, Ordering::Relaxed);
+
+ let mut chan = wait_lock(&self.chan);
+ chan.pull_pending(false);
+ if let Some((_, sending)) = chan.sending.as_ref() {
+ sending.iter().for_each(|hook| {
+ hook.signal().fire();
+ })
+ }
+ chan.waiting.iter().for_each(|hook| {
+ hook.signal().fire();
+ });
+ }
+
+ fn is_disconnected(&self) -> bool {
+ self.disconnected.load(Ordering::SeqCst)
+ }
+
+ fn is_empty(&self) -> bool {
+ self.len() == 0
+ }
+
+ fn is_full(&self) -> bool {
+ self.capacity().map(|cap| cap == self.len()).unwrap_or(false)
+ }
+
+ fn len(&self) -> usize {
+ let mut chan = wait_lock(&self.chan);
+ chan.pull_pending(false);
+ chan.queue.len()
+ }
+
+ fn capacity(&self) -> Option<usize> {
+ wait_lock(&self.chan).sending.as_ref().map(|(cap, _)| *cap)
+ }
+
+ fn sender_count(&self) -> usize {
+ self.sender_count.load(Ordering::Relaxed)
+ }
+
+ fn receiver_count(&self) -> usize {
+ self.receiver_count.load(Ordering::Relaxed)
+ }
+}
+
+/// A transmitting end of a channel.
+pub struct Sender<T> {
+ shared: Arc<Shared<T>>,
+}
+
+impl<T> Sender<T> {
+ /// Attempt to send a value into the channel. If the channel is bounded and full, or all
+ /// receivers have been dropped, an error is returned. If the channel associated with this
+ /// sender is unbounded, this method has the same behaviour as [`Sender::send`].
+ pub fn try_send(&self, msg: T) -> Result<(), TrySendError<T>> {
+ self.shared.send_sync(msg, None).map_err(|err| match err {
+ TrySendTimeoutError::Full(msg) => TrySendError::Full(msg),
+ TrySendTimeoutError::Disconnected(msg) => TrySendError::Disconnected(msg),
+ _ => unreachable!(),
+ })
+ }
+
+ /// Send a value into the channel, returning an error if all receivers have been dropped.
+ /// If the channel is bounded and is full, this method will block until space is available
+ /// or all receivers have been dropped. If the channel is unbounded, this method will not
+ /// block.
+ pub fn send(&self, msg: T) -> Result<(), SendError<T>> {
+ self.shared.send_sync(msg, Some(None)).map_err(|err| match err {
+ TrySendTimeoutError::Disconnected(msg) => SendError(msg),
+ _ => unreachable!(),
+ })
+ }
+
+ /// Send a value into the channel, returning an error if all receivers have been dropped
+ /// or the deadline has passed. If the channel is bounded and is full, this method will
+ /// block until space is available, the deadline is reached, or all receivers have been
+ /// dropped.
+ pub fn send_deadline(&self, msg: T, deadline: Instant) -> Result<(), SendTimeoutError<T>> {
+ self.shared.send_sync(msg, Some(Some(deadline))).map_err(|err| match err {
+ TrySendTimeoutError::Disconnected(msg) => SendTimeoutError::Disconnected(msg),
+ TrySendTimeoutError::Timeout(msg) => SendTimeoutError::Timeout(msg),
+ _ => unreachable!(),
+ })
+ }
+
+ /// Send a value into the channel, returning an error if all receivers have been dropped
+ /// or the timeout has expired. If the channel is bounded and is full, this method will
+ /// block until space is available, the timeout has expired, or all receivers have been
+ /// dropped.
+ pub fn send_timeout(&self, msg: T, dur: Duration) -> Result<(), SendTimeoutError<T>> {
+ self.send_deadline(msg, Instant::now().checked_add(dur).unwrap())
+ }
+
+ /// Returns true if all receivers for this channel have been dropped.
+ pub fn is_disconnected(&self) -> bool {
+ self.shared.is_disconnected()
+ }
+
+ /// Returns true if the channel is empty.
+ /// Note: Zero-capacity channels are always empty.
+ pub fn is_empty(&self) -> bool {
+ self.shared.is_empty()
+ }
+
+ /// Returns true if the channel is full.
+ /// Note: Zero-capacity channels are always full.
+ pub fn is_full(&self) -> bool {
+ self.shared.is_full()
+ }
+
+ /// Returns the number of messages in the channel
+ pub fn len(&self) -> usize {
+ self.shared.len()
+ }
+
+ /// If the channel is bounded, returns its capacity.
+ pub fn capacity(&self) -> Option<usize> {
+ self.shared.capacity()
+ }
+
+ /// Get the number of senders that currently exist, including this one.
+ pub fn sender_count(&self) -> usize {
+ self.shared.sender_count()
+ }
+
+ /// Get the number of receivers that currently exist.
+ ///
+ /// Note that this method makes no guarantees that a subsequent send will succeed; it's
+ /// possible that between `receiver_count()` being called and a `send()`, all open receivers
+ /// could drop.
+ pub fn receiver_count(&self) -> usize {
+ self.shared.receiver_count()
+ }
+
+ /// Creates a [`WeakSender`] that does not keep the channel open.
+ ///
+ /// The channel is closed once all `Sender`s are dropped, even if there
+ /// are still active `WeakSender`s.
+ pub fn downgrade(&self) -> WeakSender<T> {
+ WeakSender {
+ shared: Arc::downgrade(&self.shared),
+ }
+ }
+
+ /// Returns whether the senders are belong to the same channel.
+ pub fn same_channel(&self, other: &Sender<T>) -> bool {
+ Arc::ptr_eq(&self.shared, &other.shared)
+ }
+}
+
+impl<T> Clone for Sender<T> {
+ /// Clone this sender. [`Sender`] acts as a handle to the ending a channel. Remaining channel
+ /// contents will only be cleaned up when all senders and the receiver have been dropped.
+ fn clone(&self) -> Self {
+ self.shared.sender_count.fetch_add(1, Ordering::Relaxed);
+ Self { shared: self.shared.clone() }
+ }
+}
+
+impl<T> fmt::Debug for Sender<T> {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ f.debug_struct("Sender").finish()
+ }
+}
+
+impl<T> Drop for Sender<T> {
+ fn drop(&mut self) {
+ // Notify receivers that all senders have been dropped if the number of senders drops to 0.
+ if self.shared.sender_count.fetch_sub(1, Ordering::Relaxed) == 1 {
+ self.shared.disconnect_all();
+ }
+ }
+}
+
+/// A sender that does not prevent the channel from being closed.
+///
+/// Weak senders do not count towards the number of active senders on the channel. As soon as
+/// all normal [`Sender`]s are dropped, the channel is closed, even if there is still a
+/// `WeakSender`.
+///
+/// To send messages, a `WeakSender` must first be upgraded to a `Sender` using the [`upgrade`]
+/// method.
+pub struct WeakSender<T> {
+ shared: Weak<Shared<T>>,
+}
+
+impl<T> WeakSender<T> {
+ /// Tries to upgrade the `WeakSender` to a [`Sender`], in order to send messages.
+ ///
+ /// Returns `None` if the channel was closed already. Note that a `Some` return value
+ /// does not guarantee that the channel is still open.
+ pub fn upgrade(&self) -> Option<Sender<T>> {
+ self.shared
+ .upgrade()
+ // check that there are still live senders
+ .filter(|shared| {
+ shared
+ .sender_count
+ .fetch_update(Ordering::Relaxed, Ordering::Relaxed, |count| {
+ if count == 0 {
+ // all senders are closed already -> don't increase the sender count
+ None
+ } else {
+ // there is still at least one active sender
+ Some(count + 1)
+ }
+ })
+ .is_ok()
+ })
+ .map(|shared| Sender { shared })
+ }
+}
+
+/// The receiving end of a channel.
+///
+/// Note: Cloning the receiver *does not* turn this channel into a broadcast channel.
+/// Each message will only be received by a single receiver. This is useful for
+/// implementing work stealing for concurrent programs.
+pub struct Receiver<T> {
+ shared: Arc<Shared<T>>,
+}
+
+impl<T> Receiver<T> {
+ /// Attempt to fetch an incoming value from the channel associated with this receiver,
+ /// returning an error if the channel is empty or if all senders have been dropped.
+ pub fn try_recv(&self) -> Result<T, TryRecvError> {
+ self.shared.recv_sync(None).map_err(|err| match err {
+ TryRecvTimeoutError::Disconnected => TryRecvError::Disconnected,
+ TryRecvTimeoutError::Empty => TryRecvError::Empty,
+ _ => unreachable!(),
+ })
+ }
+
+ /// Wait for an incoming value from the channel associated with this receiver, returning an
+ /// error if all senders have been dropped.
+ pub fn recv(&self) -> Result<T, RecvError> {
+ self.shared.recv_sync(Some(None)).map_err(|err| match err {
+ TryRecvTimeoutError::Disconnected => RecvError::Disconnected,
+ _ => unreachable!(),
+ })
+ }
+
+ /// Wait for an incoming value from the channel associated with this receiver, returning an
+ /// error if all senders have been dropped or the deadline has passed.
+ pub fn recv_deadline(&self, deadline: Instant) -> Result<T, RecvTimeoutError> {
+ self.shared.recv_sync(Some(Some(deadline))).map_err(|err| match err {
+ TryRecvTimeoutError::Disconnected => RecvTimeoutError::Disconnected,
+ TryRecvTimeoutError::Timeout => RecvTimeoutError::Timeout,
+ _ => unreachable!(),
+ })
+ }
+
+ /// Wait for an incoming value from the channel associated with this receiver, returning an
+ /// error if all senders have been dropped or the timeout has expired.
+ pub fn recv_timeout(&self, dur: Duration) -> Result<T, RecvTimeoutError> {
+ self.recv_deadline(Instant::now().checked_add(dur).unwrap())
+ }
+
+ /// Create a blocking iterator over the values received on the channel that finishes iteration
+ /// when all senders have been dropped.
+ ///
+ /// You can also create a self-owned iterator with [`Receiver::into_iter`].
+ pub fn iter(&self) -> Iter<T> {
+ Iter { receiver: &self }
+ }
+
+ /// A non-blocking iterator over the values received on the channel that finishes iteration
+ /// when all senders have been dropped or the channel is empty.
+ pub fn try_iter(&self) -> TryIter<T> {
+ TryIter { receiver: &self }
+ }
+
+ /// Take all msgs currently sitting in the channel and produce an iterator over them. Unlike
+ /// `try_iter`, the iterator will not attempt to fetch any more values from the channel once
+ /// the function has been called.
+ pub fn drain(&self) -> Drain<T> {
+ let mut chan = wait_lock(&self.shared.chan);
+ chan.pull_pending(false);
+ let queue = std::mem::take(&mut chan.queue);
+
+ Drain { queue, _phantom: PhantomData }
+ }
+
+ /// Returns true if all senders for this channel have been dropped.
+ pub fn is_disconnected(&self) -> bool {
+ self.shared.is_disconnected()
+ }
+
+ /// Returns true if the channel is empty.
+ /// Note: Zero-capacity channels are always empty.
+ pub fn is_empty(&self) -> bool {
+ self.shared.is_empty()
+ }
+
+ /// Returns true if the channel is full.
+ /// Note: Zero-capacity channels are always full.
+ pub fn is_full(&self) -> bool {
+ self.shared.is_full()
+ }
+
+ /// Returns the number of messages in the channel.
+ pub fn len(&self) -> usize {
+ self.shared.len()
+ }
+
+ /// If the channel is bounded, returns its capacity.
+ pub fn capacity(&self) -> Option<usize> {
+ self.shared.capacity()
+ }
+
+ /// Get the number of senders that currently exist.
+ pub fn sender_count(&self) -> usize {
+ self.shared.sender_count()
+ }
+
+ /// Get the number of receivers that currently exist, including this one.
+ pub fn receiver_count(&self) -> usize {
+ self.shared.receiver_count()
+ }
+
+ /// Returns whether the receivers are belong to the same channel.
+ pub fn same_channel(&self, other: &Receiver<T>) -> bool {
+ Arc::ptr_eq(&self.shared, &other.shared)
+ }
+}
+
+impl<T> Clone for Receiver<T> {
+ /// Clone this receiver. [`Receiver`] acts as a handle to the ending a channel. Remaining
+ /// channel contents will only be cleaned up when all senders and the receiver have been
+ /// dropped.
+ ///
+ /// Note: Cloning the receiver *does not* turn this channel into a broadcast channel.
+ /// Each message will only be received by a single receiver. This is useful for
+ /// implementing work stealing for concurrent programs.
+ fn clone(&self) -> Self {
+ self.shared.receiver_count.fetch_add(1, Ordering::Relaxed);
+ Self { shared: self.shared.clone() }
+ }
+}
+
+impl<T> fmt::Debug for Receiver<T> {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ f.debug_struct("Receiver").finish()
+ }
+}
+
+impl<T> Drop for Receiver<T> {
+ fn drop(&mut self) {
+ // Notify senders that all receivers have been dropped if the number of receivers drops
+ // to 0.
+ if self.shared.receiver_count.fetch_sub(1, Ordering::Relaxed) == 1 {
+ self.shared.disconnect_all();
+ }
+ }
+}
+
+/// This exists as a shorthand for [`Receiver::iter`].
+impl<'a, T> IntoIterator for &'a Receiver<T> {
+ type Item = T;
+ type IntoIter = Iter<'a, T>;
+
+ fn into_iter(self) -> Self::IntoIter {
+ Iter { receiver: self }
+ }
+}
+
+impl<T> IntoIterator for Receiver<T> {
+ type Item = T;
+ type IntoIter = IntoIter<T>;
+
+ /// Creates a self-owned but semantically equivalent alternative to [`Receiver::iter`].
+ fn into_iter(self) -> Self::IntoIter {
+ IntoIter { receiver: self }
+ }
+}
+
+/// An iterator over the msgs received from a channel.
+pub struct Iter<'a, T> {
+ receiver: &'a Receiver<T>,
+}
+
+impl<'a, T> Iterator for Iter<'a, T> {
+ type Item = T;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ self.receiver.recv().ok()
+ }
+}
+
+/// An non-blocking iterator over the msgs received from a channel.
+pub struct TryIter<'a, T> {
+ receiver: &'a Receiver<T>,
+}
+
+impl<'a, T> Iterator for TryIter<'a, T> {
+ type Item = T;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ self.receiver.try_recv().ok()
+ }
+}
+
+/// An fixed-sized iterator over the msgs drained from a channel.
+#[derive(Debug)]
+pub struct Drain<'a, T> {
+ queue: VecDeque<T>,
+ /// A phantom field used to constrain the lifetime of this iterator. We do this because the
+ /// implementation may change and we don't want to unintentionally constrain it. Removing this
+ /// lifetime later is a possibility.
+ _phantom: PhantomData<&'a ()>,
+}
+
+impl<'a, T> Iterator for Drain<'a, T> {
+ type Item = T;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ self.queue.pop_front()
+ }
+}
+
+impl<'a, T> ExactSizeIterator for Drain<'a, T> {
+ fn len(&self) -> usize {
+ self.queue.len()
+ }
+}
+
+/// An owned iterator over the msgs received from a channel.
+pub struct IntoIter<T> {
+ receiver: Receiver<T>,
+}
+
+impl<T> Iterator for IntoIter<T> {
+ type Item = T;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ self.receiver.recv().ok()
+ }
+}
+
+/// Create a channel with no maximum capacity.
+///
+/// Create an unbounded channel with a [`Sender`] and [`Receiver`] connected to each end respectively. Values sent in
+/// one end of the channel will be received on the other end. The channel is thread-safe, and both [`Sender`] and
+/// [`Receiver`] may be sent to or shared between threads as necessary. In addition, both [`Sender`] and [`Receiver`]
+/// may be cloned.
+///
+/// # Examples
+/// ```
+/// let (tx, rx) = flume::unbounded();
+///
+/// tx.send(42).unwrap();
+/// assert_eq!(rx.recv().unwrap(), 42);
+/// ```
+pub fn unbounded<T>() -> (Sender<T>, Receiver<T>) {
+ let shared = Arc::new(Shared::new(None));
+ (
+ Sender { shared: shared.clone() },
+ Receiver { shared },
+ )
+}
+
+/// Create a channel with a maximum capacity.
+///
+/// Create a bounded channel with a [`Sender`] and [`Receiver`] connected to each end respectively. Values sent in one
+/// end of the channel will be received on the other end. The channel is thread-safe, and both [`Sender`] and
+/// [`Receiver`] may be sent to or shared between threads as necessary. In addition, both [`Sender`] and [`Receiver`]
+/// may be cloned.
+///
+/// Unlike an [`unbounded`] channel, if there is no space left for new messages, calls to
+/// [`Sender::send`] will block (unblocking once a receiver has made space). If blocking behaviour
+/// is not desired, [`Sender::try_send`] may be used.
+///
+/// Like `std::sync::mpsc`, `flume` supports 'rendezvous' channels. A bounded queue with a maximum capacity of zero
+/// will block senders until a receiver is available to take the value. You can imagine a rendezvous channel as a
+/// ['Glienicke Bridge'](https://en.wikipedia.org/wiki/Glienicke_Bridge)-style location at which senders and receivers
+/// perform a handshake and transfer ownership of a value.
+///
+/// # Examples
+/// ```
+/// let (tx, rx) = flume::bounded(32);
+///
+/// for i in 1..33 {
+/// tx.send(i).unwrap();
+/// }
+/// assert!(tx.try_send(33).is_err());
+///
+/// assert_eq!(rx.try_iter().sum::<u32>(), (1..33).sum());
+/// ```
+pub fn bounded<T>(cap: usize) -> (Sender<T>, Receiver<T>) {
+ let shared = Arc::new(Shared::new(Some(cap)));
+ (
+ Sender { shared: shared.clone() },
+ Receiver { shared },
+ )
+}
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