Struct async_broadcast::Receiver

pub struct Receiver<T> { /* private fields */ }

The receiving side of a channel.

Receivers can be cloned and shared among threads. When all (active) receivers associated with a channel are dropped, the channel becomes closed. You can deactivate a receiver using Receiver::deactivate if you would like the channel to remain open without keeping active receivers around.

Implementations

impl<T> Receiver<T>

pub fn capacity(&self) -> usize

Returns the channel capacity.

Examples

use async_broadcast::broadcast;

let (_s, r) = broadcast::<i32>(5);
assert_eq!(r.capacity(), 5);

pub fn set_capacity(&mut self, new_cap: usize)

Set the channel capacity.

There are times when you need to change the channel’s capacity after creating it. If the new_cap is less than the number of messages in the channel, the oldest messages will be dropped to shrink the channel.

Examples

use async_broadcast::{broadcast, TrySendError, TryRecvError};

let (s, mut r) = broadcast::<i32>(3);
assert_eq!(r.capacity(), 3);
s.try_broadcast(1).unwrap();
s.try_broadcast(2).unwrap();
s.try_broadcast(3).unwrap();

r.set_capacity(1);
assert_eq!(r.capacity(), 1);
assert_eq!(r.try_recv(), Err(TryRecvError::Overflowed(2)));
assert_eq!(r.try_recv().unwrap(), 3);
assert_eq!(r.try_recv(), Err(TryRecvError::Empty));
s.try_broadcast(1).unwrap();
assert_eq!(s.try_broadcast(2), Err(TrySendError::Full(2)));

r.set_capacity(2);
assert_eq!(r.capacity(), 2);
s.try_broadcast(2).unwrap();
assert_eq!(s.try_broadcast(2), Err(TrySendError::Full(2)));

pub fn overflow(&self) -> bool

If overflow mode is enabled on this channel.

Examples

use async_broadcast::broadcast;

let (_s, r) = broadcast::<i32>(5);
assert!(!r.overflow());

pub fn set_overflow(&mut self, overflow: bool)

Set overflow mode on the channel.

When overflow mode is set, broadcasting to the channel will succeed even if the channel is full. It achieves that by removing the oldest message from the channel.

Examples

use async_broadcast::{broadcast, TrySendError, TryRecvError};

let (s, mut r) = broadcast::<i32>(2);
s.try_broadcast(1).unwrap();
s.try_broadcast(2).unwrap();
assert_eq!(s.try_broadcast(3), Err(TrySendError::Full(3)));
r.set_overflow(true);
assert_eq!(s.try_broadcast(3).unwrap(), Some(1));
assert_eq!(s.try_broadcast(4).unwrap(), Some(2));

assert_eq!(r.try_recv(), Err(TryRecvError::Overflowed(2)));
assert_eq!(r.try_recv().unwrap(), 3);
assert_eq!(r.try_recv().unwrap(), 4);
assert_eq!(r.try_recv(), Err(TryRecvError::Empty));

pub fn await_active(&self) -> bool

If sender will wait for active receivers.

If set to false, Send will resolve immediately with a SendError. Defaults to true.

Examples

use async_broadcast::broadcast;

let (_, r) = broadcast::<i32>(5);
assert!(r.await_active());

pub fn set_await_active(&mut self, await_active: bool)

Specify if sender will wait for active receivers.

If set to false, Send will resolve immediately with a SendError. Defaults to true.

Examples

use async_broadcast::broadcast;

let (s, mut r) = broadcast::<i32>(2);
s.broadcast(1).await.unwrap();

r.set_await_active(false);
let _ = r.deactivate();
assert!(s.broadcast(2).await.is_err());

pub fn close(&self) -> bool

Closes the channel.

Returns true if this call has closed the channel and it was not closed already.

The remaining messages can still be received.

Examples

use async_broadcast::{broadcast, RecvError};

let (s, mut r) = broadcast(1);
s.broadcast(1).await.unwrap();
assert!(s.close());

assert_eq!(r.recv().await.unwrap(), 1);
assert_eq!(r.recv().await, Err(RecvError::Closed));

pub fn is_closed(&self) -> bool

Returns true if the channel is closed.

Examples

use async_broadcast::{broadcast, RecvError};

let (s, r) = broadcast::<()>(1);
assert!(!s.is_closed());

drop(r);
assert!(s.is_closed());

pub fn is_empty(&self) -> bool

Returns true if the channel is empty.

Examples

use async_broadcast::broadcast;

let (s, r) = broadcast(1);

assert!(s.is_empty());
s.broadcast(1).await;
assert!(!s.is_empty());

pub fn is_full(&self) -> bool

Returns true if the channel is full.

Examples

use async_broadcast::broadcast;

let (s, r) = broadcast(1);

assert!(!s.is_full());
s.broadcast(1).await;
assert!(s.is_full());

pub fn len(&self) -> usize

Returns the number of messages in the channel.

Examples

use async_broadcast::broadcast;

let (s, r) = broadcast(2);
assert_eq!(s.len(), 0);

s.broadcast(1).await;
s.broadcast(2).await;
assert_eq!(s.len(), 2);

pub fn receiver_count(&self) -> usize

Returns the number of receivers for the channel.

This does not include inactive receivers. Use Receiver::inactive_receiver_count if you are interested in that.

Examples

use async_broadcast::broadcast;

let (s, r) = broadcast::<()>(1);
assert_eq!(s.receiver_count(), 1);
let r = r.deactivate();
assert_eq!(s.receiver_count(), 0);

let r2 = r.activate_cloned();
assert_eq!(r.receiver_count(), 1);
assert_eq!(r.inactive_receiver_count(), 1);

pub fn inactive_receiver_count(&self) -> usize

Returns the number of inactive receivers for the channel.

Examples

use async_broadcast::broadcast;

let (s, r) = broadcast::<()>(1);
assert_eq!(s.receiver_count(), 1);
let r = r.deactivate();
assert_eq!(s.receiver_count(), 0);

let r2 = r.activate_cloned();
assert_eq!(r.receiver_count(), 1);
assert_eq!(r.inactive_receiver_count(), 1);

pub fn sender_count(&self) -> usize

Returns the number of senders for the channel.

Examples

use async_broadcast::broadcast;

let (s, r) = broadcast::<()>(1);
assert_eq!(s.sender_count(), 1);

let s2 = s.clone();
assert_eq!(s.sender_count(), 2);

pub fn deactivate(self) -> InactiveReceiver<T>

Downgrade to a InactiveReceiver.

An inactive receiver is one that can not and does not receive any messages. Its only purpose is keep the associated channel open even when there are no (active) receivers. An inactive receiver can be upgraded into a Receiver using InactiveReceiver::activate or InactiveReceiver::activate_cloned.

Sender::try_broadcast will return TrySendError::Inactive if only inactive receivers exists for the associated channel and Sender::broadcast will wait until an active receiver is available.

Examples

use async_broadcast::{broadcast, TrySendError};

let (s, r) = broadcast(1);
let inactive = r.deactivate();
assert_eq!(s.try_broadcast(10), Err(TrySendError::Inactive(10)));

let mut r = inactive.activate();
assert_eq!(s.broadcast(10).await, Ok(None));
assert_eq!(r.recv().await, Ok(10));

impl<T: Clone> Receiver<T>

pub fn recv(&mut self) -> Pin<Box<Recv<'_, T>>>

Receives a message from the channel.

If the channel is empty, this method waits until there is a message.

If the channel is closed, this method receives a message or returns an error if there are no more messages.

If this receiver has missed a message (only possible if overflow mode is enabled), then this method returns an error and readjusts its cursor to point to the first available message.

The future returned by this function is pinned to the heap. If the future being Unpin is not important to you, or if you just .await this future, use the [recv_direct] method instead.

Examples

use async_broadcast::{broadcast, RecvError};

let (s, mut r1) = broadcast(1);
let mut r2 = r1.clone();

assert_eq!(s.broadcast(1).await, Ok(None));
drop(s);

assert_eq!(r1.recv().await, Ok(1));
assert_eq!(r1.recv().await, Err(RecvError::Closed));
assert_eq!(r2.recv().await, Ok(1));
assert_eq!(r2.recv().await, Err(RecvError::Closed));

pub fn recv_direct(&mut self) -> Recv<'_, T>

Receives a message from the channel without pinning the future to the heap.

The future returned by this method is not Unpin and must be pinned before use. This is the desired behavior if you just .await on the future. For other uses cases, use the [recv] method instead.

Examples

use async_broadcast::{broadcast, RecvError};

let (s, mut r1) = broadcast(1);
let mut r2 = r1.clone();

assert_eq!(s.broadcast(1).await, Ok(None));
drop(s);

assert_eq!(r1.recv_direct().await, Ok(1));
assert_eq!(r1.recv_direct().await, Err(RecvError::Closed));
assert_eq!(r2.recv_direct().await, Ok(1));
assert_eq!(r2.recv_direct().await, Err(RecvError::Closed));

pub fn try_recv(&mut self) -> Result<T, TryRecvError>

Attempts to receive a message from the channel.

If the channel is empty or closed, this method returns an error.

If this receiver has missed a message (only possible if overflow mode is enabled), then this method returns an error and readjusts its cursor to point to the first available message.

Examples

use async_broadcast::{broadcast, TryRecvError};

let (s, mut r1) = broadcast(1);
let mut r2 = r1.clone();
assert_eq!(s.broadcast(1).await, Ok(None));

assert_eq!(r1.try_recv(), Ok(1));
assert_eq!(r1.try_recv(), Err(TryRecvError::Empty));
assert_eq!(r2.try_recv(), Ok(1));
assert_eq!(r2.try_recv(), Err(TryRecvError::Empty));

drop(s);
assert_eq!(r1.try_recv(), Err(TryRecvError::Closed));
assert_eq!(r2.try_recv(), Err(TryRecvError::Closed));

pub fn new_sender(&self) -> Sender<T>

Produce a new Sender for this channel.

This will not re-open the channel if it was closed due to all senders being dropped.

Examples

use async_broadcast::{broadcast, RecvError};

let (s1, mut r) = broadcast(2);

assert_eq!(s1.broadcast(1).await, Ok(None));

let mut s2 = r.new_sender();

assert_eq!(s2.broadcast(2).await, Ok(None));
drop(s1);
drop(s2);

assert_eq!(r.recv().await, Ok(1));
assert_eq!(r.recv().await, Ok(2));
assert_eq!(r.recv().await, Err(RecvError::Closed));

pub fn new_receiver(&self) -> Self

Produce a new Receiver for this channel.

Unlike Receiver::clone, this method creates a new receiver that starts with zero messages available. This is slightly faster than a real clone.

Examples

use async_broadcast::{broadcast, RecvError};

let (s, mut r1) = broadcast(2);

assert_eq!(s.broadcast(1).await, Ok(None));

let mut r2 = r1.new_receiver();

assert_eq!(s.broadcast(2).await, Ok(None));
drop(s);

assert_eq!(r1.recv().await, Ok(1));
assert_eq!(r1.recv().await, Ok(2));
assert_eq!(r1.recv().await, Err(RecvError::Closed));

assert_eq!(r2.recv().await, Ok(2));
assert_eq!(r2.recv().await, Err(RecvError::Closed));

pub fn poll_recv( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Option<Result<T, RecvError>>>

A low level poll method that is similar to Receiver::recv() or Receiver::recv_direct(), and can be useful for building stream implementations which use a Receiver under the hood and want to know if the stream has overflowed.

Prefer to use Receiver::recv() or Receiver::recv_direct() when otherwise possible.

Errors

If the number of messages that have been sent has overflowed the channel capacity, a RecvError::Overflowed variant is returned containing the number of items that overflowed and were lost.

Examples

This example shows how the Receiver::poll_recv method can be used to allow a custom stream implementation to internally make use of a Receiver. This example implementation differs from the stream implementation of Receiver because it returns an error if the channel capacity overflows, which the built in Receiver stream doesn’t do.

use futures_core::Stream;
use async_broadcast::{Receiver, RecvError};
use std::{pin::Pin, task::{Poll, Context}};

struct MyStream(Receiver<i32>);

impl futures_core::Stream for MyStream {
    type Item = Result<i32, RecvError>;
    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        Pin::new(&mut self.0).poll_recv(cx)
    }
}

Trait Implementations

impl<T> Clone for Receiver<T>

fn clone(&self) -> Self

Produce a clone of this Receiver that has the same messages queued.

Examples

use async_broadcast::{broadcast, RecvError};

let (s, mut r1) = broadcast(1);

assert_eq!(s.broadcast(1).await, Ok(None));
drop(s);

let mut r2 = r1.clone();

assert_eq!(r1.recv().await, Ok(1));
assert_eq!(r1.recv().await, Err(RecvError::Closed));
assert_eq!(r2.recv().await, Ok(1));
assert_eq!(r2.recv().await, Err(RecvError::Closed));

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Debug> Debug for Receiver<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> Drop for Receiver<T>

fn drop(&mut self)

Executes the destructor for this type.

impl<T: Clone> FusedStream for Receiver<T>

fn is_terminated(&self) -> bool

Returns true if the stream should no longer be polled.

impl<T: Clone> Stream for Receiver<T>

type Item = T

Values yielded by the stream.

fn poll_next( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Option<Self::Item>>

Attempt to pull out the next value of this stream, registering the current task for wakeup if the value is not yet available, and returning None if the stream is exhausted.

fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the stream.