Struct tokio::sync::mpsc::Receiver

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

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

Attempts to return a pending value on this receiver without blocking.

This method will never block the caller in order to wait for data to become available. Instead, this will always return immediately with a possible option of pending data on the channel.

This is useful for a flavor of “optimistic check” before deciding to block on a receiver.

Compared with recv, this function has two failure cases instead of one (one for disconnection, one for an empty buffer).

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.
}

Trait Implementations

impl<T> Debug for Receiver<T>

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

Formats the value using the given formatter.

impl<T> Stream for Receiver<T>

type Item = T

Values yielded by the stream.

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

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.

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

Returns the bounds on the remaining length of the stream.

impl<T> Unpin for Receiver<T>