Struct local_sync::oneshot::Receiver

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

Receive a value from the associated Sender.

A pair of both a Sender and a Receiver are created by the channel function.

Examples

use local_sync::oneshot;

#[monoio::main]
async fn main() {
    let (tx, rx) = oneshot::channel();

    monoio::spawn(async move {
        if let Err(_) = tx.send(3) {
            println!("the receiver dropped");
        }
    });

    match rx.await {
        Ok(v) => println!("got = {:?}", v),
        Err(_) => println!("the sender dropped"),
    }
}

If the sender is dropped without sending, the receiver will fail with error::RecvError:

use local_sync::oneshot;

#[monoio::main]
async fn main() {
    let (tx, rx) = oneshot::channel::<u32>();

    monoio::spawn(async move {
        drop(tx);
    });

    match rx.await {
        Ok(_) => panic!("This doesn't happen"),
        Err(_) => println!("the sender dropped"),
    }
}

Implementations

impl<T> Receiver<T>

pub fn close(&mut self)

Prevents the associated Sender handle from sending a value.

Any send operation which happens after calling close is guaranteed to fail. After calling close, try_recv should be called to receive a value if one was sent before the call to close completed.

This function is useful to perform a graceful shutdown and ensure that a value will not be sent into the channel and never received.

close is no-op if a message is already received or the channel is already closed.

Examples

Prevent a value from being sent

use local_sync::oneshot;
use local_sync::oneshot::error::TryRecvError;

#[monoio::main]
async fn main() {
    let (tx, mut rx) = oneshot::channel();

    assert!(!tx.is_closed());

    rx.close();

    assert!(tx.is_closed());
    assert!(tx.send("never received").is_err());

    match rx.try_recv() {
        Err(TryRecvError::Closed) => {}
        _ => unreachable!(),
    }
}

Receive a value sent before calling close

use local_sync::oneshot;

#[monoio::main]
async fn main() {
    let (tx, mut rx) = oneshot::channel();

    assert!(tx.send("will receive").is_ok());

    rx.close();

    let msg = rx.try_recv().unwrap();
    assert_eq!(msg, "will receive");
}

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

Attempts to receive a value.

If a pending value exists in the channel, it is returned. If no value has been sent, the current task will not be registered for future notification.

This function is useful to call from outside the context of an asynchronous task.

Return

• Ok(T) if a value is pending in the channel.
• Err(TryRecvError::Empty) if no value has been sent yet.
• Err(TryRecvError::Closed) if the sender has dropped without sending a value.

Examples

try_recv before a value is sent, then after.

use local_sync::oneshot;
use local_sync::oneshot::error::TryRecvError;

#[monoio::main]
async fn main() {
    let (tx, mut rx) = oneshot::channel();

    match rx.try_recv() {
        // The channel is currently empty
        Err(TryRecvError::Empty) => {}
        _ => unreachable!(),
    }

    // Send a value
    tx.send("hello").unwrap();

    match rx.try_recv() {
        Ok(value) => assert_eq!(value, "hello"),
        _ => unreachable!(),
    }
}

try_recv when the sender dropped before sending a value

use local_sync::oneshot;
use local_sync::oneshot::error::TryRecvError;

#[monoio::main]
async fn main() {
    let (tx, mut rx) = oneshot::channel::<()>();

    drop(tx);

    match rx.try_recv() {
        // The channel will never receive a value.
        Err(TryRecvError::Closed) => {}
        _ => unreachable!(),
    }
}

Trait Implementations

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> Future for Receiver<T>

type Output = Result<T, RecvError>

The type of value produced on completion.

fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>

Attempt to resolve the future to a final value, registering the current task for wakeup if the value is not yet available.