Struct tokio::sync::mpsc::Receiver

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

This is supported on crate feature sync only.

Receive values from the associated Sender.

Instances are created by the channel function.

Implementations

impl<T> Receiver<T>

pub async fn recv(&mut self) -> Option<T>

Receives the next value for this receiver.

None is returned when all Sender halves have dropped, indicating that no further values can be sent on the channel.

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 fn blocking_recv(&mut self) -> Option<T>

Blocking receive to call outside of asynchronous contexts.

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()
}

pub fn close(&mut self)

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.

In order to guarantee no messages are dropped, after calling close(), recv() must be called until None is returned.

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 poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<T>>

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.
• 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, only the Waker from the Context passed to the most recent call is scheduled to receive a wakeup.

Trait Implementations

impl<T> Debug for Receiver<T>

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

Formats the value using the given formatter.

impl<T> Unpin for Receiver<T>