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use crate::loom::sync::Arc;
use crate::sync::batch_semaphore::{self as semaphore, TryAcquireError};
use crate::sync::mpsc::chan;
use crate::sync::mpsc::error::{SendError, TryRecvError, TrySendError};
cfg_time! {
use crate::sync::mpsc::error::SendTimeoutError;
use crate::time::Duration;
}
use std::fmt;
use std::task::{Context, Poll};
/// Sends values to the associated `Receiver`.
///
/// Instances are created by the [`channel`] function.
///
/// To convert the `Sender` into a `Sink` or use it in a poll function, you can
/// use the [`PollSender`] utility.
///
pub struct Sender<T> {
chan: chan::Tx<T, Semaphore>,
}
/// A sender that does not prevent the channel from being closed.
///
/// If all [`Sender`] instances of a channel were dropped and only `WeakSender`
/// instances remain, the channel is closed.
///
/// In order to send messages, the `WeakSender` needs to be upgraded using
/// [`WeakSender::upgrade`], which returns `Option<Sender>`. It returns `None`
/// if all `Sender`s have been dropped, and otherwise it returns a `Sender`.
///
/// [`Sender`]: Sender
/// [`WeakSender::upgrade`]: WeakSender::upgrade
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc::channel;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, _rx) = channel::<i32>(15);
/// let tx_weak = tx.downgrade();
///
/// // Upgrading will succeed because `tx` still exists.
/// assert!(tx_weak.upgrade().is_some());
///
/// // If we drop `tx`, then it will fail.
/// drop(tx);
/// assert!(tx_weak.clone().upgrade().is_none());
/// }
/// ```
pub struct WeakSender<T> {
chan: Arc<chan::Chan<T, Semaphore>>,
}
/// Permits to send one value into the channel.
///
/// `Permit` values are returned by [`Sender::reserve()`] and [`Sender::try_reserve()`]
/// and are used to guarantee channel capacity before generating a message to send.
///
/// [`Sender::reserve()`]: Sender::reserve
/// [`Sender::try_reserve()`]: Sender::try_reserve
pub struct Permit<'a, T> {
chan: &'a chan::Tx<T, Semaphore>,
}
/// An [`Iterator`] of [`Permit`] that can be used to hold `n` slots in the channel.
///
/// `PermitIterator` values are returned by [`Sender::reserve_many()`] and [`Sender::try_reserve_many()`]
/// and are used to guarantee channel capacity before generating `n` messages to send.
///
/// [`Sender::reserve_many()`]: Sender::reserve_many
/// [`Sender::try_reserve_many()`]: Sender::try_reserve_many
pub struct PermitIterator<'a, T> {
chan: &'a chan::Tx<T, Semaphore>,
n: usize,
}
/// Owned permit to send one value into the channel.
///
/// This is identical to the [`Permit`] type, except that it moves the sender
/// rather than borrowing it.
///
/// `OwnedPermit` values are returned by [`Sender::reserve_owned()`] and
/// [`Sender::try_reserve_owned()`] and are used to guarantee channel capacity
/// before generating a message to send.
///
/// [`Permit`]: Permit
/// [`Sender::reserve_owned()`]: Sender::reserve_owned
/// [`Sender::try_reserve_owned()`]: Sender::try_reserve_owned
pub struct OwnedPermit<T> {
chan: Option<chan::Tx<T, Semaphore>>,
}
/// Receives values from the associated `Sender`.
///
/// Instances are created by the [`channel`] function.
///
/// This receiver can be turned into a `Stream` using [`ReceiverStream`].
///
/// [`ReceiverStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.ReceiverStream.html
pub struct Receiver<T> {
/// The channel receiver.
chan: chan::Rx<T, Semaphore>,
}
/// Creates a bounded mpsc channel for communicating between asynchronous tasks
/// with backpressure.
///
/// The channel will buffer up to the provided number of messages. Once the
/// buffer is full, attempts to send new messages will wait until a message is
/// received from the channel. The provided buffer capacity must be at least 1.
///
/// All data sent on `Sender` will become available on `Receiver` in the same
/// order as it was sent.
///
/// The `Sender` can be cloned to `send` to the same channel from multiple code
/// locations. Only one `Receiver` is supported.
///
/// If the `Receiver` is disconnected while trying to `send`, the `send` method
/// will return a `SendError`. Similarly, if `Sender` is disconnected while
/// trying to `recv`, the `recv` method will return `None`.
///
/// # Panics
///
/// Panics if the buffer capacity is 0.
///
/// # Examples
///
/// ```rust
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(100);
///
/// tokio::spawn(async move {
/// for i in 0..10 {
/// if let Err(_) = tx.send(i).await {
/// println!("receiver dropped");
/// return;
/// }
/// }
/// });
///
/// while let Some(i) = rx.recv().await {
/// println!("got = {}", i);
/// }
/// }
/// ```
#[track_caller]
pub fn channel<T>(buffer: usize) -> (Sender<T>, Receiver<T>) {
assert!(buffer > 0, "mpsc bounded channel requires buffer > 0");
let semaphore = Semaphore {
semaphore: semaphore::Semaphore::new(buffer),
bound: buffer,
};
let (tx, rx) = chan::channel(semaphore);
let tx = Sender::new(tx);
let rx = Receiver::new(rx);
(tx, rx)
}
/// Channel semaphore is a tuple of the semaphore implementation and a `usize`
/// representing the channel bound.
#[derive(Debug)]
pub(crate) struct Semaphore {
pub(crate) semaphore: semaphore::Semaphore,
pub(crate) bound: usize,
}
impl<T> Receiver<T> {
pub(crate) fn new(chan: chan::Rx<T, Semaphore>) -> Receiver<T> {
Receiver { chan }
}
/// Receives the next value for this receiver.
///
/// This method returns `None` if the channel has been closed and there are
/// no remaining messages in the channel's buffer. This indicates that no
/// further values can ever be received from this `Receiver`. The channel is
/// closed when all senders have been dropped, or when [`close`] is called.
///
/// If there are no messages in the channel's buffer, but the channel has
/// not yet been closed, this method will sleep until a message is sent or
/// the channel is closed. Note that if [`close`] is called, but there are
/// still outstanding [`Permits`] from before it was closed, the channel is
/// not considered closed by `recv` until the permits are released.
///
/// # Cancel safety
///
/// This method is cancel safe. If `recv` is used as the event in a
/// [`tokio::select!`](crate::select) statement and some other branch
/// completes first, it is guaranteed that no messages were received on this
/// channel.
///
/// [`close`]: Self::close
/// [`Permits`]: struct@crate::sync::mpsc::Permit
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(100);
///
/// tokio::spawn(async move {
/// tx.send("hello").await.unwrap();
/// });
///
/// assert_eq!(Some("hello"), rx.recv().await);
/// assert_eq!(None, rx.recv().await);
/// }
/// ```
///
/// Values are buffered:
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(100);
///
/// tx.send("hello").await.unwrap();
/// tx.send("world").await.unwrap();
///
/// assert_eq!(Some("hello"), rx.recv().await);
/// assert_eq!(Some("world"), rx.recv().await);
/// }
/// ```
pub async fn recv(&mut self) -> Option<T> {
use crate::future::poll_fn;
poll_fn(|cx| self.chan.recv(cx)).await
}
/// Receives the next values for this receiver and extends `buffer`.
///
/// This method extends `buffer` by no more than a fixed number of values
/// as specified by `limit`. If `limit` is zero, the function immediately
/// returns `0`. The return value is the number of values added to `buffer`.
///
/// For `limit > 0`, if there are no messages in the channel's queue, but
/// the channel has not yet been closed, this method will sleep until a
/// message is sent or the channel is closed. Note that if [`close`] is
/// called, but there are still outstanding [`Permits`] from before it was
/// closed, the channel is not considered closed by `recv_many` until the
/// permits are released.
///
/// For non-zero values of `limit`, this method will never return `0` unless
/// the channel has been closed and there are no remaining messages in the
/// channel's queue. This indicates that no further values can ever be
/// received from this `Receiver`. The channel is closed when all senders
/// have been dropped, or when [`close`] is called.
///
/// The capacity of `buffer` is increased as needed.
///
/// # Cancel safety
///
/// This method is cancel safe. If `recv_many` is used as the event in a
/// [`tokio::select!`](crate::select) statement and some other branch
/// completes first, it is guaranteed that no messages were received on this
/// channel.
///
/// [`close`]: Self::close
/// [`Permits`]: struct@crate::sync::mpsc::Permit
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let mut buffer: Vec<&str> = Vec::with_capacity(2);
/// let limit = 2;
/// let (tx, mut rx) = mpsc::channel(100);
/// let tx2 = tx.clone();
/// tx2.send("first").await.unwrap();
/// tx2.send("second").await.unwrap();
/// tx2.send("third").await.unwrap();
///
/// // Call `recv_many` to receive up to `limit` (2) values.
/// assert_eq!(2, rx.recv_many(&mut buffer, limit).await);
/// assert_eq!(vec!["first", "second"], buffer);
///
/// // If the buffer is full, the next call to `recv_many`
/// // reserves additional capacity.
/// assert_eq!(1, rx.recv_many(&mut buffer, 1).await);
///
/// tokio::spawn(async move {
/// tx.send("fourth").await.unwrap();
/// });
///
/// // 'tx' is dropped, but `recv_many`
/// // is guaranteed not to return 0 as the channel
/// // is not yet closed.
/// assert_eq!(1, rx.recv_many(&mut buffer, 1).await);
/// assert_eq!(vec!["first", "second", "third", "fourth"], buffer);
///
/// // Once the last sender is dropped, the channel is
/// // closed and `recv_many` returns 0, capacity unchanged.
/// drop(tx2);
/// assert_eq!(0, rx.recv_many(&mut buffer, limit).await);
/// assert_eq!(vec!["first", "second", "third", "fourth"], buffer);
/// }
/// ```
pub async fn recv_many(&mut self, buffer: &mut Vec<T>, limit: usize) -> usize {
use crate::future::poll_fn;
poll_fn(|cx| self.chan.recv_many(cx, buffer, limit)).await
}
/// Tries to receive the next value for this receiver.
///
/// This method returns the [`Empty`] error if the channel is currently
/// empty, but there are still outstanding [senders] or [permits].
///
/// This method returns the [`Disconnected`] error if the channel is
/// currently empty, and there are no outstanding [senders] or [permits].
///
/// Unlike the [`poll_recv`] method, this method will never return an
/// [`Empty`] error spuriously.
///
/// [`Empty`]: crate::sync::mpsc::error::TryRecvError::Empty
/// [`Disconnected`]: crate::sync::mpsc::error::TryRecvError::Disconnected
/// [`poll_recv`]: Self::poll_recv
/// [senders]: crate::sync::mpsc::Sender
/// [permits]: crate::sync::mpsc::Permit
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
/// use tokio::sync::mpsc::error::TryRecvError;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(100);
///
/// tx.send("hello").await.unwrap();
///
/// assert_eq!(Ok("hello"), rx.try_recv());
/// assert_eq!(Err(TryRecvError::Empty), rx.try_recv());
///
/// tx.send("hello").await.unwrap();
/// // Drop the last sender, closing the channel.
/// drop(tx);
///
/// assert_eq!(Ok("hello"), rx.try_recv());
/// assert_eq!(Err(TryRecvError::Disconnected), rx.try_recv());
/// }
/// ```
pub fn try_recv(&mut self) -> Result<T, TryRecvError> {
self.chan.try_recv()
}
/// Blocking receive to call outside of asynchronous contexts.
///
/// This method returns `None` if the channel has been closed and there are
/// no remaining messages in the channel's buffer. This indicates that no
/// further values can ever be received from this `Receiver`. The channel is
/// closed when all senders have been dropped, or when [`close`] is called.
///
/// If there are no messages in the channel's buffer, but the channel has
/// not yet been closed, this method will block until a message is sent or
/// the channel is closed.
///
/// This method is intended for use cases where you are sending from
/// asynchronous code to synchronous code, and will work even if the sender
/// is not using [`blocking_send`] to send the message.
///
/// Note that if [`close`] is called, but there are still outstanding
/// [`Permits`] from before it was closed, the channel is not considered
/// closed by `blocking_recv` until the permits are released.
///
/// [`close`]: Self::close
/// [`Permits`]: struct@crate::sync::mpsc::Permit
/// [`blocking_send`]: fn@crate::sync::mpsc::Sender::blocking_send
///
/// # Panics
///
/// This function panics if called within an asynchronous execution
/// context.
///
/// # Examples
///
/// ```
/// use std::thread;
/// use tokio::runtime::Runtime;
/// use tokio::sync::mpsc;
///
/// fn main() {
/// let (tx, mut rx) = mpsc::channel::<u8>(10);
///
/// let sync_code = thread::spawn(move || {
/// assert_eq!(Some(10), rx.blocking_recv());
/// });
///
/// Runtime::new()
/// .unwrap()
/// .block_on(async move {
/// let _ = tx.send(10).await;
/// });
/// sync_code.join().unwrap()
/// }
/// ```
#[track_caller]
#[cfg(feature = "sync")]
#[cfg_attr(docsrs, doc(alias = "recv_blocking"))]
pub fn blocking_recv(&mut self) -> Option<T> {
crate::future::block_on(self.recv())
}
/// Closes the receiving half of a channel without dropping it.
///
/// This prevents any further messages from being sent on the channel while
/// still enabling the receiver to drain messages that are buffered. Any
/// outstanding [`Permit`] values will still be able to send messages.
///
/// To guarantee that no messages are dropped, after calling `close()`,
/// `recv()` must be called until `None` is returned. If there are
/// outstanding [`Permit`] or [`OwnedPermit`] values, the `recv` method will
/// not return `None` until those are released.
///
/// [`Permit`]: Permit
/// [`OwnedPermit`]: OwnedPermit
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(20);
///
/// tokio::spawn(async move {
/// let mut i = 0;
/// while let Ok(permit) = tx.reserve().await {
/// permit.send(i);
/// i += 1;
/// }
/// });
///
/// rx.close();
///
/// while let Some(msg) = rx.recv().await {
/// println!("got {}", msg);
/// }
///
/// // Channel closed and no messages are lost.
/// }
/// ```
pub fn close(&mut self) {
self.chan.close();
}
/// Checks if a channel is closed.
///
/// This method returns `true` if the channel has been closed. The channel is closed
/// when all [`Sender`] have been dropped, or when [`Receiver::close`] is called.
///
/// [`Sender`]: crate::sync::mpsc::Sender
/// [`Receiver::close`]: crate::sync::mpsc::Receiver::close
///
/// # Examples
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (_tx, mut rx) = mpsc::channel::<()>(10);
/// assert!(!rx.is_closed());
///
/// rx.close();
///
/// assert!(rx.is_closed());
/// }
/// ```
pub fn is_closed(&self) -> bool {
self.chan.is_closed()
}
/// Checks if a channel is empty.
///
/// This method returns `true` if the channel has no messages.
///
/// # Examples
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, rx) = mpsc::channel(10);
/// assert!(rx.is_empty());
///
/// tx.send(0).await.unwrap();
/// assert!(!rx.is_empty());
/// }
///
/// ```
pub fn is_empty(&self) -> bool {
self.chan.is_empty()
}
/// Returns the number of messages in the channel.
///
/// # Examples
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, rx) = mpsc::channel(10);
/// assert_eq!(0, rx.len());
///
/// tx.send(0).await.unwrap();
/// assert_eq!(1, rx.len());
/// }
/// ```
pub fn len(&self) -> usize {
self.chan.len()
}
/// Returns the current capacity of the channel.
///
/// The capacity goes down when the sender sends a value by calling [`Sender::send`] or by reserving
/// capacity with [`Sender::reserve`]. The capacity goes up when values are received.
/// This is distinct from [`max_capacity`], which always returns buffer capacity initially
/// specified when calling [`channel`].
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel::<()>(5);
///
/// assert_eq!(rx.capacity(), 5);
///
/// // Making a reservation drops the capacity by one.
/// let permit = tx.reserve().await.unwrap();
/// assert_eq!(rx.capacity(), 4);
/// assert_eq!(rx.len(), 0);
///
/// // Sending and receiving a value increases the capacity by one.
/// permit.send(());
/// assert_eq!(rx.len(), 1);
/// rx.recv().await.unwrap();
/// assert_eq!(rx.capacity(), 5);
///
/// // Directly sending a message drops the capacity by one.
/// tx.send(()).await.unwrap();
/// assert_eq!(rx.capacity(), 4);
/// assert_eq!(rx.len(), 1);
///
/// // Receiving the message increases the capacity by one.
/// rx.recv().await.unwrap();
/// assert_eq!(rx.capacity(), 5);
/// assert_eq!(rx.len(), 0);
/// }
/// ```
/// [`capacity`]: Receiver::capacity
/// [`max_capacity`]: Receiver::max_capacity
pub fn capacity(&self) -> usize {
self.chan.semaphore().semaphore.available_permits()
}
/// Returns the maximum buffer capacity of the channel.
///
/// The maximum capacity is the buffer capacity initially specified when calling
/// [`channel`]. This is distinct from [`capacity`], which returns the *current*
/// available buffer capacity: as messages are sent and received, the value
/// returned by [`capacity`] will go up or down, whereas the value
/// returned by [`max_capacity`] will remain constant.
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, rx) = mpsc::channel::<()>(5);
///
/// // both max capacity and capacity are the same at first
/// assert_eq!(rx.max_capacity(), 5);
/// assert_eq!(rx.capacity(), 5);
///
/// // Making a reservation doesn't change the max capacity.
/// let permit = tx.reserve().await.unwrap();
/// assert_eq!(rx.max_capacity(), 5);
/// // but drops the capacity by one
/// assert_eq!(rx.capacity(), 4);
/// }
/// ```
/// [`capacity`]: Receiver::capacity
/// [`max_capacity`]: Receiver::max_capacity
pub fn max_capacity(&self) -> usize {
self.chan.semaphore().bound
}
/// Polls to receive the next message on this channel.
///
/// This method returns:
///
/// * `Poll::Pending` if no messages are available but the channel is not
/// closed, or if a spurious failure happens.
/// * `Poll::Ready(Some(message))` if a message is available.
/// * `Poll::Ready(None)` if the channel has been closed and all messages
/// sent before it was closed have been received.
///
/// When the method returns `Poll::Pending`, the `Waker` in the provided
/// `Context` is scheduled to receive a wakeup when a message is sent on any
/// receiver, or when the channel is closed. Note that on multiple calls to
/// `poll_recv` or `poll_recv_many`, only the `Waker` from the `Context`
/// passed to the most recent call is scheduled to receive a wakeup.
///
/// If this method returns `Poll::Pending` due to a spurious failure, then
/// the `Waker` will be notified when the situation causing the spurious
/// failure has been resolved. Note that receiving such a wakeup does not
/// guarantee that the next call will succeed — it could fail with another
/// spurious failure.
pub fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<T>> {
self.chan.recv(cx)
}
/// Polls to receive multiple messages on this channel, extending the provided buffer.
///
/// This method returns:
/// * `Poll::Pending` if no messages are available but the channel is not closed, or if a
/// spurious failure happens.
/// * `Poll::Ready(count)` where `count` is the number of messages successfully received and
/// stored in `buffer`. This can be less than, or equal to, `limit`.
/// * `Poll::Ready(0)` if `limit` is set to zero or when the channel is closed.
///
/// When the method returns `Poll::Pending`, the `Waker` in the provided
/// `Context` is scheduled to receive a wakeup when a message is sent on any
/// receiver, or when the channel is closed. Note that on multiple calls to
/// `poll_recv` or `poll_recv_many`, only the `Waker` from the `Context`
/// passed to the most recent call is scheduled to receive a wakeup.
///
/// Note that this method does not guarantee that exactly `limit` messages
/// are received. Rather, if at least one message is available, it returns
/// as many messages as it can up to the given limit. This method returns
/// zero only if the channel is closed (or if `limit` is zero).
///
/// # Examples
///
/// ```
/// use std::task::{Context, Poll};
/// use std::pin::Pin;
/// use tokio::sync::mpsc;
/// use futures::Future;
///
/// struct MyReceiverFuture<'a> {
/// receiver: mpsc::Receiver<i32>,
/// buffer: &'a mut Vec<i32>,
/// limit: usize,
/// }
///
/// impl<'a> Future for MyReceiverFuture<'a> {
/// type Output = usize; // Number of messages received
///
/// fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
/// let MyReceiverFuture { receiver, buffer, limit } = &mut *self;
///
/// // Now `receiver` and `buffer` are mutable references, and `limit` is copied
/// match receiver.poll_recv_many(cx, *buffer, *limit) {
/// Poll::Pending => Poll::Pending,
/// Poll::Ready(count) => Poll::Ready(count),
/// }
/// }
/// }
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, rx) = mpsc::channel(32);
/// let mut buffer = Vec::new();
///
/// let my_receiver_future = MyReceiverFuture {
/// receiver: rx,
/// buffer: &mut buffer,
/// limit: 3,
/// };
///
/// for i in 0..10 {
/// tx.send(i).await.unwrap();
/// }
///
/// let count = my_receiver_future.await;
/// assert_eq!(count, 3);
/// assert_eq!(buffer, vec![0,1,2])
/// }
/// ```
pub fn poll_recv_many(
&mut self,
cx: &mut Context<'_>,
buffer: &mut Vec<T>,
limit: usize,
) -> Poll<usize> {
self.chan.recv_many(cx, buffer, limit)
}
/// Returns the number of [`Sender`] handles.
pub fn sender_strong_count(&self) -> usize {
self.chan.sender_strong_count()
}
/// Returns the number of [`WeakSender`] handles.
pub fn sender_weak_count(&self) -> usize {
self.chan.sender_weak_count()
}
}
impl<T> fmt::Debug for Receiver<T> {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("Receiver")
.field("chan", &self.chan)
.finish()
}
}
impl<T> Unpin for Receiver<T> {}
impl<T> Sender<T> {
pub(crate) fn new(chan: chan::Tx<T, Semaphore>) -> Sender<T> {
Sender { chan }
}
/// Sends a value, waiting until there is capacity.
///
/// A successful send occurs when it is determined that the other end of the
/// channel has not hung up already. An unsuccessful send would be one where
/// the corresponding receiver has already been closed. Note that a return
/// value of `Err` means that the data will never be received, but a return
/// value of `Ok` does not mean that the data will be received. It is
/// possible for the corresponding receiver to hang up immediately after
/// this function returns `Ok`.
///
/// # Errors
///
/// If the receive half of the channel is closed, either due to [`close`]
/// being called or the [`Receiver`] handle dropping, the function returns
/// an error. The error includes the value passed to `send`.
///
/// [`close`]: Receiver::close
/// [`Receiver`]: Receiver
///
/// # Cancel safety
///
/// If `send` is used as the event in a [`tokio::select!`](crate::select)
/// statement and some other branch completes first, then it is guaranteed
/// that the message was not sent. **However, in that case, the message
/// is dropped and will be lost.**
///
/// To avoid losing messages, use [`reserve`](Self::reserve) to reserve
/// capacity, then use the returned [`Permit`] to send the message.
///
/// This channel uses a queue to ensure that calls to `send` and `reserve`
/// complete in the order they were requested. Cancelling a call to
/// `send` makes you lose your place in the queue.
///
/// # Examples
///
/// In the following example, each call to `send` will block until the
/// previously sent value was received.
///
/// ```rust
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(1);
///
/// tokio::spawn(async move {
/// for i in 0..10 {
/// if let Err(_) = tx.send(i).await {
/// println!("receiver dropped");
/// return;
/// }
/// }
/// });
///
/// while let Some(i) = rx.recv().await {
/// println!("got = {}", i);
/// }
/// }
/// ```
pub async fn send(&self, value: T) -> Result<(), SendError<T>> {
match self.reserve().await {
Ok(permit) => {
permit.send(value);
Ok(())
}
Err(_) => Err(SendError(value)),
}
}
/// Completes when the receiver has dropped.
///
/// This allows the producers to get notified when interest in the produced
/// values is canceled and immediately stop doing work.
///
/// # Cancel safety
///
/// This method is cancel safe. Once the channel is closed, it stays closed
/// forever and all future calls to `closed` will return immediately.
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx1, rx) = mpsc::channel::<()>(1);
/// let tx2 = tx1.clone();
/// let tx3 = tx1.clone();
/// let tx4 = tx1.clone();
/// let tx5 = tx1.clone();
/// tokio::spawn(async move {
/// drop(rx);
/// });
///
/// futures::join!(
/// tx1.closed(),
/// tx2.closed(),
/// tx3.closed(),
/// tx4.closed(),
/// tx5.closed()
/// );
/// println!("Receiver dropped");
/// }
/// ```
pub async fn closed(&self) {
self.chan.closed().await;
}
/// Attempts to immediately send a message on this `Sender`
///
/// This method differs from [`send`] by returning immediately if the channel's
/// buffer is full or no receiver is waiting to acquire some data. Compared
/// with [`send`], this function has two failure cases instead of one (one for
/// disconnection, one for a full buffer).
///
/// # Errors
///
/// If the channel capacity has been reached, i.e., the channel has `n`
/// buffered values where `n` is the argument passed to [`channel`], then an
/// error is returned.
///
/// If the receive half of the channel is closed, either due to [`close`]
/// being called or the [`Receiver`] handle dropping, the function returns
/// an error. The error includes the value passed to `send`.
///
/// [`send`]: Sender::send
/// [`channel`]: channel
/// [`close`]: Receiver::close
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// // Create a channel with buffer size 1
/// let (tx1, mut rx) = mpsc::channel(1);
/// let tx2 = tx1.clone();
///
/// tokio::spawn(async move {
/// tx1.send(1).await.unwrap();
/// tx1.send(2).await.unwrap();
/// // task waits until the receiver receives a value.
/// });
///
/// tokio::spawn(async move {
/// // This will return an error and send
/// // no message if the buffer is full
/// let _ = tx2.try_send(3);
/// });
///
/// let mut msg;
/// msg = rx.recv().await.unwrap();
/// println!("message {} received", msg);
///
/// msg = rx.recv().await.unwrap();
/// println!("message {} received", msg);
///
/// // Third message may have never been sent
/// match rx.recv().await {
/// Some(msg) => println!("message {} received", msg),
/// None => println!("the third message was never sent"),
/// }
/// }
/// ```
pub fn try_send(&self, message: T) -> Result<(), TrySendError<T>> {
match self.chan.semaphore().semaphore.try_acquire(1) {
Ok(()) => {}
Err(TryAcquireError::Closed) => return Err(TrySendError::Closed(message)),
Err(TryAcquireError::NoPermits) => return Err(TrySendError::Full(message)),
}
// Send the message
self.chan.send(message);
Ok(())
}
/// Sends a value, waiting until there is capacity, but only for a limited time.
///
/// Shares the same success and error conditions as [`send`], adding one more
/// condition for an unsuccessful send, which is when the provided timeout has
/// elapsed, and there is no capacity available.
///
/// [`send`]: Sender::send
///
/// # Errors
///
/// If the receive half of the channel is closed, either due to [`close`]
/// being called or the [`Receiver`] having been dropped,
/// the function returns an error. The error includes the value passed to `send`.
///
/// [`close`]: Receiver::close
/// [`Receiver`]: Receiver
///
/// # Panics
///
/// This function panics if it is called outside the context of a Tokio
/// runtime [with time enabled](crate::runtime::Builder::enable_time).
///
/// # Examples
///
/// In the following example, each call to `send_timeout` will block until the
/// previously sent value was received, unless the timeout has elapsed.
///
/// ```rust
/// use tokio::sync::mpsc;
/// use tokio::time::{sleep, Duration};
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(1);
///
/// tokio::spawn(async move {
/// for i in 0..10 {
/// if let Err(e) = tx.send_timeout(i, Duration::from_millis(100)).await {
/// println!("send error: #{:?}", e);
/// return;
/// }
/// }
/// });
///
/// while let Some(i) = rx.recv().await {
/// println!("got = {}", i);
/// sleep(Duration::from_millis(200)).await;
/// }
/// }
/// ```
#[cfg(feature = "time")]
#[cfg_attr(docsrs, doc(cfg(feature = "time")))]
pub async fn send_timeout(
&self,
value: T,
timeout: Duration,
) -> Result<(), SendTimeoutError<T>> {
let permit = match crate::time::timeout(timeout, self.reserve()).await {
Err(_) => {
return Err(SendTimeoutError::Timeout(value));
}
Ok(Err(_)) => {
return Err(SendTimeoutError::Closed(value));
}
Ok(Ok(permit)) => permit,
};
permit.send(value);
Ok(())
}
/// Blocking send to call outside of asynchronous contexts.
///
/// This method is intended for use cases where you are sending from
/// synchronous code to asynchronous code, and will work even if the
/// receiver is not using [`blocking_recv`] to receive the message.
///
/// [`blocking_recv`]: fn@crate::sync::mpsc::Receiver::blocking_recv
///
/// # Panics
///
/// This function panics if called within an asynchronous execution
/// context.
///
/// # Examples
///
/// ```
/// use std::thread;
/// use tokio::runtime::Runtime;
/// use tokio::sync::mpsc;
///
/// fn main() {
/// let (tx, mut rx) = mpsc::channel::<u8>(1);
///
/// let sync_code = thread::spawn(move || {
/// tx.blocking_send(10).unwrap();
/// });
///
/// Runtime::new().unwrap().block_on(async move {
/// assert_eq!(Some(10), rx.recv().await);
/// });
/// sync_code.join().unwrap()
/// }
/// ```
#[track_caller]
#[cfg(feature = "sync")]
#[cfg_attr(docsrs, doc(alias = "send_blocking"))]
pub fn blocking_send(&self, value: T) -> Result<(), SendError<T>> {
crate::future::block_on(self.send(value))
}
/// Checks if the channel has been closed. This happens when the
/// [`Receiver`] is dropped, or when the [`Receiver::close`] method is
/// called.
///
/// [`Receiver`]: crate::sync::mpsc::Receiver
/// [`Receiver::close`]: crate::sync::mpsc::Receiver::close
///
/// ```
/// let (tx, rx) = tokio::sync::mpsc::channel::<()>(42);
/// assert!(!tx.is_closed());
///
/// let tx2 = tx.clone();
/// assert!(!tx2.is_closed());
///
/// drop(rx);
/// assert!(tx.is_closed());
/// assert!(tx2.is_closed());
/// ```
pub fn is_closed(&self) -> bool {
self.chan.is_closed()
}
/// Waits for channel capacity. Once capacity to send one message is
/// available, it is reserved for the caller.
///
/// If the channel is full, the function waits for the number of unreceived
/// messages to become less than the channel capacity. Capacity to send one
/// message is reserved for the caller. A [`Permit`] is returned to track
/// the reserved capacity. The [`send`] function on [`Permit`] consumes the
/// reserved capacity.
///
/// Dropping [`Permit`] without sending a message releases the capacity back
/// to the channel.
///
/// [`Permit`]: Permit
/// [`send`]: Permit::send
///
/// # Cancel safety
///
/// This channel uses a queue to ensure that calls to `send` and `reserve`
/// complete in the order they were requested. Cancelling a call to
/// `reserve` makes you lose your place in the queue.
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(1);
///
/// // Reserve capacity
/// let permit = tx.reserve().await.unwrap();
///
/// // Trying to send directly on the `tx` will fail due to no
/// // available capacity.
/// assert!(tx.try_send(123).is_err());
///
/// // Sending on the permit succeeds
/// permit.send(456);
///
/// // The value sent on the permit is received
/// assert_eq!(rx.recv().await.unwrap(), 456);
/// }
/// ```
pub async fn reserve(&self) -> Result<Permit<'_, T>, SendError<()>> {
self.reserve_inner(1).await?;
Ok(Permit { chan: &self.chan })
}
/// Waits for channel capacity. Once capacity to send `n` messages is
/// available, it is reserved for the caller.
///
/// If the channel is full or if there are fewer than `n` permits available, the function waits
/// for the number of unreceived messages to become `n` less than the channel capacity.
/// Capacity to send `n` message is then reserved for the caller.
///
/// A [`PermitIterator`] is returned to track the reserved capacity.
/// You can call this [`Iterator`] until it is exhausted to
/// get a [`Permit`] and then call [`Permit::send`]. This function is similar to
/// [`try_reserve_many`] except it awaits for the slots to become available.
///
/// If the channel is closed, the function returns a [`SendError`].
///
/// Dropping [`PermitIterator`] without consuming it entirely releases the remaining
/// permits back to the channel.
///
/// [`PermitIterator`]: PermitIterator
/// [`Permit`]: Permit
/// [`send`]: Permit::send
/// [`try_reserve_many`]: Sender::try_reserve_many
///
/// # Cancel safety
///
/// This channel uses a queue to ensure that calls to `send` and `reserve_many`
/// complete in the order they were requested. Cancelling a call to
/// `reserve_many` makes you lose your place in the queue.
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(2);
///
/// // Reserve capacity
/// let mut permit = tx.reserve_many(2).await.unwrap();
///
/// // Trying to send directly on the `tx` will fail due to no
/// // available capacity.
/// assert!(tx.try_send(123).is_err());
///
/// // Sending with the permit iterator succeeds
/// permit.next().unwrap().send(456);
/// permit.next().unwrap().send(457);
///
/// // The iterator should now be exhausted
/// assert!(permit.next().is_none());
///
/// // The value sent on the permit is received
/// assert_eq!(rx.recv().await.unwrap(), 456);
/// assert_eq!(rx.recv().await.unwrap(), 457);
/// }
/// ```
pub async fn reserve_many(&self, n: usize) -> Result<PermitIterator<'_, T>, SendError<()>> {
self.reserve_inner(n).await?;
Ok(PermitIterator {
chan: &self.chan,
n,
})
}
/// Waits for channel capacity, moving the `Sender` and returning an owned
/// permit. Once capacity to send one message is available, it is reserved
/// for the caller.
///
/// This moves the sender _by value_, and returns an owned permit that can
/// be used to send a message into the channel. Unlike [`Sender::reserve`],
/// this method may be used in cases where the permit must be valid for the
/// `'static` lifetime. `Sender`s may be cloned cheaply (`Sender::clone` is
/// essentially a reference count increment, comparable to [`Arc::clone`]),
/// so when multiple [`OwnedPermit`]s are needed or the `Sender` cannot be
/// moved, it can be cloned prior to calling `reserve_owned`.
///
/// If the channel is full, the function waits for the number of unreceived
/// messages to become less than the channel capacity. Capacity to send one
/// message is reserved for the caller. An [`OwnedPermit`] is returned to
/// track the reserved capacity. The [`send`] function on [`OwnedPermit`]
/// consumes the reserved capacity.
///
/// Dropping the [`OwnedPermit`] without sending a message releases the
/// capacity back to the channel.
///
/// # Cancel safety
///
/// This channel uses a queue to ensure that calls to `send` and `reserve`
/// complete in the order they were requested. Cancelling a call to
/// `reserve_owned` makes you lose your place in the queue.
///
/// # Examples
/// Sending a message using an [`OwnedPermit`]:
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(1);
///
/// // Reserve capacity, moving the sender.
/// let permit = tx.reserve_owned().await.unwrap();
///
/// // Send a message, consuming the permit and returning
/// // the moved sender.
/// let tx = permit.send(123);
///
/// // The value sent on the permit is received.
/// assert_eq!(rx.recv().await.unwrap(), 123);
///
/// // The sender can now be used again.
/// tx.send(456).await.unwrap();
/// }
/// ```
///
/// When multiple [`OwnedPermit`]s are needed, or the sender cannot be moved
/// by value, it can be inexpensively cloned before calling `reserve_owned`:
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(1);
///
/// // Clone the sender and reserve capacity.
/// let permit = tx.clone().reserve_owned().await.unwrap();
///
/// // Trying to send directly on the `tx` will fail due to no
/// // available capacity.
/// assert!(tx.try_send(123).is_err());
///
/// // Sending on the permit succeeds.
/// permit.send(456);
///
/// // The value sent on the permit is received
/// assert_eq!(rx.recv().await.unwrap(), 456);
/// }
/// ```
///
/// [`Sender::reserve`]: Sender::reserve
/// [`OwnedPermit`]: OwnedPermit
/// [`send`]: OwnedPermit::send
/// [`Arc::clone`]: std::sync::Arc::clone
pub async fn reserve_owned(self) -> Result<OwnedPermit<T>, SendError<()>> {
self.reserve_inner(1).await?;
Ok(OwnedPermit {
chan: Some(self.chan),
})
}
async fn reserve_inner(&self, n: usize) -> Result<(), SendError<()>> {
crate::trace::async_trace_leaf().await;
if n > self.max_capacity() {
return Err(SendError(()));
}
match self.chan.semaphore().semaphore.acquire(n).await {
Ok(()) => Ok(()),
Err(_) => Err(SendError(())),
}
}
/// Tries to acquire a slot in the channel without waiting for the slot to become
/// available.
///
/// If the channel is full this function will return [`TrySendError`], otherwise
/// if there is a slot available it will return a [`Permit`] that will then allow you
/// to [`send`] on the channel with a guaranteed slot. This function is similar to
/// [`reserve`] except it does not await for the slot to become available.
///
/// Dropping [`Permit`] without sending a message releases the capacity back
/// to the channel.
///
/// [`Permit`]: Permit
/// [`send`]: Permit::send
/// [`reserve`]: Sender::reserve
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(1);
///
/// // Reserve capacity
/// let permit = tx.try_reserve().unwrap();
///
/// // Trying to send directly on the `tx` will fail due to no
/// // available capacity.
/// assert!(tx.try_send(123).is_err());
///
/// // Trying to reserve an additional slot on the `tx` will
/// // fail because there is no capacity.
/// assert!(tx.try_reserve().is_err());
///
/// // Sending on the permit succeeds
/// permit.send(456);
///
/// // The value sent on the permit is received
/// assert_eq!(rx.recv().await.unwrap(), 456);
///
/// }
/// ```
pub fn try_reserve(&self) -> Result<Permit<'_, T>, TrySendError<()>> {
match self.chan.semaphore().semaphore.try_acquire(1) {
Ok(()) => {}
Err(TryAcquireError::Closed) => return Err(TrySendError::Closed(())),
Err(TryAcquireError::NoPermits) => return Err(TrySendError::Full(())),
}
Ok(Permit { chan: &self.chan })
}
/// Tries to acquire `n` slots in the channel without waiting for the slot to become
/// available.
///
/// A [`PermitIterator`] is returned to track the reserved capacity.
/// You can call this [`Iterator`] until it is exhausted to
/// get a [`Permit`] and then call [`Permit::send`]. This function is similar to
/// [`reserve_many`] except it does not await for the slots to become available.
///
/// If there are fewer than `n` permits available on the channel, then
/// this function will return a [`TrySendError::Full`]. If the channel is closed
/// this function will return a [`TrySendError::Closed`].
///
/// Dropping [`PermitIterator`] without consuming it entirely releases the remaining
/// permits back to the channel.
///
/// [`PermitIterator`]: PermitIterator
/// [`send`]: Permit::send
/// [`reserve_many`]: Sender::reserve_many
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(2);
///
/// // Reserve capacity
/// let mut permit = tx.try_reserve_many(2).unwrap();
///
/// // Trying to send directly on the `tx` will fail due to no
/// // available capacity.
/// assert!(tx.try_send(123).is_err());
///
/// // Trying to reserve an additional slot on the `tx` will
/// // fail because there is no capacity.
/// assert!(tx.try_reserve().is_err());
///
/// // Sending with the permit iterator succeeds
/// permit.next().unwrap().send(456);
/// permit.next().unwrap().send(457);
///
/// // The iterator should now be exhausted
/// assert!(permit.next().is_none());
///
/// // The value sent on the permit is received
/// assert_eq!(rx.recv().await.unwrap(), 456);
/// assert_eq!(rx.recv().await.unwrap(), 457);
///
/// // Trying to call try_reserve_many with 0 will return an empty iterator
/// let mut permit = tx.try_reserve_many(0).unwrap();
/// assert!(permit.next().is_none());
///
/// // Trying to call try_reserve_many with a number greater than the channel
/// // capacity will return an error
/// let permit = tx.try_reserve_many(3);
/// assert!(permit.is_err());
///
/// // Trying to call try_reserve_many on a closed channel will return an error
/// drop(rx);
/// let permit = tx.try_reserve_many(1);
/// assert!(permit.is_err());
///
/// let permit = tx.try_reserve_many(0);
/// assert!(permit.is_err());
/// }
/// ```
pub fn try_reserve_many(&self, n: usize) -> Result<PermitIterator<'_, T>, TrySendError<()>> {
if n > self.max_capacity() {
return Err(TrySendError::Full(()));
}
match self.chan.semaphore().semaphore.try_acquire(n) {
Ok(()) => {}
Err(TryAcquireError::Closed) => return Err(TrySendError::Closed(())),
Err(TryAcquireError::NoPermits) => return Err(TrySendError::Full(())),
}
Ok(PermitIterator {
chan: &self.chan,
n,
})
}
/// Tries to acquire a slot in the channel without waiting for the slot to become
/// available, returning an owned permit.
///
/// This moves the sender _by value_, and returns an owned permit that can
/// be used to send a message into the channel. Unlike [`Sender::try_reserve`],
/// this method may be used in cases where the permit must be valid for the
/// `'static` lifetime. `Sender`s may be cloned cheaply (`Sender::clone` is
/// essentially a reference count increment, comparable to [`Arc::clone`]),
/// so when multiple [`OwnedPermit`]s are needed or the `Sender` cannot be
/// moved, it can be cloned prior to calling `try_reserve_owned`.
///
/// If the channel is full this function will return a [`TrySendError`].
/// Since the sender is taken by value, the `TrySendError` returned in this
/// case contains the sender, so that it may be used again. Otherwise, if
/// there is a slot available, this method will return an [`OwnedPermit`]
/// that can then be used to [`send`] on the channel with a guaranteed slot.
/// This function is similar to [`reserve_owned`] except it does not await
/// for the slot to become available.
///
/// Dropping the [`OwnedPermit`] without sending a message releases the capacity back
/// to the channel.
///
/// [`OwnedPermit`]: OwnedPermit
/// [`send`]: OwnedPermit::send
/// [`reserve_owned`]: Sender::reserve_owned
/// [`Arc::clone`]: std::sync::Arc::clone
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(1);
///
/// // Reserve capacity
/// let permit = tx.clone().try_reserve_owned().unwrap();
///
/// // Trying to send directly on the `tx` will fail due to no
/// // available capacity.
/// assert!(tx.try_send(123).is_err());
///
/// // Trying to reserve an additional slot on the `tx` will
/// // fail because there is no capacity.
/// assert!(tx.try_reserve().is_err());
///
/// // Sending on the permit succeeds
/// permit.send(456);
///
/// // The value sent on the permit is received
/// assert_eq!(rx.recv().await.unwrap(), 456);
///
/// }
/// ```
pub fn try_reserve_owned(self) -> Result<OwnedPermit<T>, TrySendError<Self>> {
match self.chan.semaphore().semaphore.try_acquire(1) {
Ok(()) => {}
Err(TryAcquireError::Closed) => return Err(TrySendError::Closed(self)),
Err(TryAcquireError::NoPermits) => return Err(TrySendError::Full(self)),
}
Ok(OwnedPermit {
chan: Some(self.chan),
})
}
/// Returns `true` if senders belong to the same channel.
///
/// # Examples
///
/// ```
/// let (tx, rx) = tokio::sync::mpsc::channel::<()>(1);
/// let tx2 = tx.clone();
/// assert!(tx.same_channel(&tx2));
///
/// let (tx3, rx3) = tokio::sync::mpsc::channel::<()>(1);
/// assert!(!tx3.same_channel(&tx2));
/// ```
pub fn same_channel(&self, other: &Self) -> bool {
self.chan.same_channel(&other.chan)
}
/// Returns the current capacity of the channel.
///
/// The capacity goes down when sending a value by calling [`send`] or by reserving capacity
/// with [`reserve`]. The capacity goes up when values are received by the [`Receiver`].
/// This is distinct from [`max_capacity`], which always returns buffer capacity initially
/// specified when calling [`channel`]
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel::<()>(5);
///
/// assert_eq!(tx.capacity(), 5);
///
/// // Making a reservation drops the capacity by one.
/// let permit = tx.reserve().await.unwrap();
/// assert_eq!(tx.capacity(), 4);
///
/// // Sending and receiving a value increases the capacity by one.
/// permit.send(());
/// rx.recv().await.unwrap();
/// assert_eq!(tx.capacity(), 5);
/// }
/// ```
///
/// [`send`]: Sender::send
/// [`reserve`]: Sender::reserve
/// [`channel`]: channel
/// [`max_capacity`]: Sender::max_capacity
pub fn capacity(&self) -> usize {
self.chan.semaphore().semaphore.available_permits()
}
/// Converts the `Sender` to a [`WeakSender`] that does not count
/// towards RAII semantics, i.e. if all `Sender` instances of the
/// channel were dropped and only `WeakSender` instances remain,
/// the channel is closed.
#[must_use = "Downgrade creates a WeakSender without destroying the original non-weak sender."]
pub fn downgrade(&self) -> WeakSender<T> {
WeakSender {
chan: self.chan.downgrade(),
}
}
/// Returns the maximum buffer capacity of the channel.
///
/// The maximum capacity is the buffer capacity initially specified when calling
/// [`channel`]. This is distinct from [`capacity`], which returns the *current*
/// available buffer capacity: as messages are sent and received, the
/// value returned by [`capacity`] will go up or down, whereas the value
/// returned by [`max_capacity`] will remain constant.
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, _rx) = mpsc::channel::<()>(5);
///
/// // both max capacity and capacity are the same at first
/// assert_eq!(tx.max_capacity(), 5);
/// assert_eq!(tx.capacity(), 5);
///
/// // Making a reservation doesn't change the max capacity.
/// let permit = tx.reserve().await.unwrap();
/// assert_eq!(tx.max_capacity(), 5);
/// // but drops the capacity by one
/// assert_eq!(tx.capacity(), 4);
/// }
/// ```
///
/// [`channel`]: channel
/// [`max_capacity`]: Sender::max_capacity
/// [`capacity`]: Sender::capacity
pub fn max_capacity(&self) -> usize {
self.chan.semaphore().bound
}
/// Returns the number of [`Sender`] handles.
pub fn strong_count(&self) -> usize {
self.chan.strong_count()
}
/// Returns the number of [`WeakSender`] handles.
pub fn weak_count(&self) -> usize {
self.chan.weak_count()
}
}
impl<T> Clone for Sender<T> {
fn clone(&self) -> Self {
Sender {
chan: self.chan.clone(),
}
}
}
impl<T> fmt::Debug for Sender<T> {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("Sender")
.field("chan", &self.chan)
.finish()
}
}
impl<T> Clone for WeakSender<T> {
fn clone(&self) -> Self {
self.chan.increment_weak_count();
WeakSender {
chan: self.chan.clone(),
}
}
}
impl<T> Drop for WeakSender<T> {
fn drop(&mut self) {
self.chan.decrement_weak_count();
}
}
impl<T> WeakSender<T> {
/// Tries to convert a `WeakSender` into a [`Sender`]. This will return `Some`
/// if there are other `Sender` instances alive and the channel wasn't
/// previously dropped, otherwise `None` is returned.
pub fn upgrade(&self) -> Option<Sender<T>> {
chan::Tx::upgrade(self.chan.clone()).map(Sender::new)
}
/// Returns the number of [`Sender`] handles.
pub fn strong_count(&self) -> usize {
self.chan.strong_count()
}
/// Returns the number of [`WeakSender`] handles.
pub fn weak_count(&self) -> usize {
self.chan.weak_count()
}
}
impl<T> fmt::Debug for WeakSender<T> {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("WeakSender").finish()
}
}
// ===== impl Permit =====
impl<T> Permit<'_, T> {
/// Sends a value using the reserved capacity.
///
/// Capacity for the message has already been reserved. The message is sent
/// to the receiver and the permit is consumed. The operation will succeed
/// even if the receiver half has been closed. See [`Receiver::close`] for
/// more details on performing a clean shutdown.
///
/// [`Receiver::close`]: Receiver::close
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(1);
///
/// // Reserve capacity
/// let permit = tx.reserve().await.unwrap();
///
/// // Trying to send directly on the `tx` will fail due to no
/// // available capacity.
/// assert!(tx.try_send(123).is_err());
///
/// // Send a message on the permit
/// permit.send(456);
///
/// // The value sent on the permit is received
/// assert_eq!(rx.recv().await.unwrap(), 456);
/// }
/// ```
pub fn send(self, value: T) {
use std::mem;
self.chan.send(value);
// Avoid the drop logic
mem::forget(self);
}
}
impl<T> Drop for Permit<'_, T> {
fn drop(&mut self) {
use chan::Semaphore;
let semaphore = self.chan.semaphore();
// Add the permit back to the semaphore
semaphore.add_permit();
// If this is the last sender for this channel, wake the receiver so
// that it can be notified that the channel is closed.
if semaphore.is_closed() && semaphore.is_idle() {
self.chan.wake_rx();
}
}
}
impl<T> fmt::Debug for Permit<'_, T> {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("Permit")
.field("chan", &self.chan)
.finish()
}
}
// ===== impl PermitIterator =====
impl<'a, T> Iterator for PermitIterator<'a, T> {
type Item = Permit<'a, T>;
fn next(&mut self) -> Option<Self::Item> {
if self.n == 0 {
return None;
}
self.n -= 1;
Some(Permit { chan: self.chan })
}
fn size_hint(&self) -> (usize, Option<usize>) {
let n = self.n;
(n, Some(n))
}
}
impl<T> ExactSizeIterator for PermitIterator<'_, T> {}
impl<T> std::iter::FusedIterator for PermitIterator<'_, T> {}
impl<T> Drop for PermitIterator<'_, T> {
fn drop(&mut self) {
use chan::Semaphore;
if self.n == 0 {
return;
}
let semaphore = self.chan.semaphore();
// Add the remaining permits back to the semaphore
semaphore.add_permits(self.n);
// If this is the last sender for this channel, wake the receiver so
// that it can be notified that the channel is closed.
if semaphore.is_closed() && semaphore.is_idle() {
self.chan.wake_rx();
}
}
}
impl<T> fmt::Debug for PermitIterator<'_, T> {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("PermitIterator")
.field("chan", &self.chan)
.field("capacity", &self.n)
.finish()
}
}
// ===== impl Permit =====
impl<T> OwnedPermit<T> {
/// Sends a value using the reserved capacity.
///
/// Capacity for the message has already been reserved. The message is sent
/// to the receiver and the permit is consumed. The operation will succeed
/// even if the receiver half has been closed. See [`Receiver::close`] for
/// more details on performing a clean shutdown.
///
/// Unlike [`Permit::send`], this method returns the [`Sender`] from which
/// the `OwnedPermit` was reserved.
///
/// [`Receiver::close`]: Receiver::close
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, mut rx) = mpsc::channel(1);
///
/// // Reserve capacity
/// let permit = tx.reserve_owned().await.unwrap();
///
/// // Send a message on the permit, returning the sender.
/// let tx = permit.send(456);
///
/// // The value sent on the permit is received
/// assert_eq!(rx.recv().await.unwrap(), 456);
///
/// // We may now reuse `tx` to send another message.
/// tx.send(789).await.unwrap();
/// }
/// ```
pub fn send(mut self, value: T) -> Sender<T> {
let chan = self.chan.take().unwrap_or_else(|| {
unreachable!("OwnedPermit channel is only taken when the permit is moved")
});
chan.send(value);
Sender { chan }
}
/// Releases the reserved capacity *without* sending a message, returning the
/// [`Sender`].
///
/// # Examples
///
/// ```
/// use tokio::sync::mpsc;
///
/// #[tokio::main]
/// async fn main() {
/// let (tx, rx) = mpsc::channel(1);
///
/// // Clone the sender and reserve capacity
/// let permit = tx.clone().reserve_owned().await.unwrap();
///
/// // Trying to send on the original `tx` will fail, since the `permit`
/// // has reserved all the available capacity.
/// assert!(tx.try_send(123).is_err());
///
/// // Release the permit without sending a message, returning the clone
/// // of the sender.
/// let tx2 = permit.release();
///
/// // We may now reuse `tx` to send another message.
/// tx.send(789).await.unwrap();
/// # drop(rx); drop(tx2);
/// }
/// ```
///
/// [`Sender`]: Sender
pub fn release(mut self) -> Sender<T> {
use chan::Semaphore;
let chan = self.chan.take().unwrap_or_else(|| {
unreachable!("OwnedPermit channel is only taken when the permit is moved")
});
// Add the permit back to the semaphore
chan.semaphore().add_permit();
Sender { chan }
}
}
impl<T> Drop for OwnedPermit<T> {
fn drop(&mut self) {
use chan::Semaphore;
// Are we still holding onto the sender?
if let Some(chan) = self.chan.take() {
let semaphore = chan.semaphore();
// Add the permit back to the semaphore
semaphore.add_permit();
// If this `OwnedPermit` is holding the last sender for this
// channel, wake the receiver so that it can be notified that the
// channel is closed.
if semaphore.is_closed() && semaphore.is_idle() {
chan.wake_rx();
}
}
// Otherwise, do nothing.
}
}
impl<T> fmt::Debug for OwnedPermit<T> {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("OwnedPermit")
.field("chan", &self.chan)
.finish()
}
}