pub struct Sender<T> { /* private fields */ }
Expand description

Sends values to the associated Receiver.

Instances are created by the channel function.

Implementations

Sends a new value via the channel, notifying all receivers.

This method fails if the channel has been closed, which happens when every receiver has been dropped.

Sends a new value via the channel, notifying all receivers and returning the previous value in the channel.

This can be useful for reusing the buffers inside a watched value. Additionally, this method permits sending values even when there are no receivers.

Examples
use tokio::sync::watch;

let (tx, _rx) = watch::channel(1);
assert_eq!(tx.send_replace(2), 1);
assert_eq!(tx.send_replace(3), 2);

Returns a reference to the most recently sent value

Outstanding borrows hold a read lock. This means that long lived borrows could cause the send half to block. It is recommended to keep the borrow as short lived as possible.

Examples
use tokio::sync::watch;

let (tx, _) = watch::channel("hello");
assert_eq!(*tx.borrow(), "hello");

Checks if the channel has been closed. This happens when all receivers have dropped.

Examples
let (tx, rx) = tokio::sync::watch::channel(());
assert!(!tx.is_closed());

drop(rx);
assert!(tx.is_closed());

Completes when all receivers have dropped.

This allows the producer 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::watch;

#[tokio::main]
async fn main() {
    let (tx, rx) = watch::channel("hello");

    tokio::spawn(async move {
        // use `rx`
        drop(rx);
    });

    // Waits for `rx` to drop
    tx.closed().await;
    println!("the `rx` handles dropped")
}

Creates a new Receiver connected to this Sender.

All messages sent before this call to subscribe are initially marked as seen by the new Receiver.

This method can be called even if there are no other receivers. In this case, the channel is reopened.

Examples

The new channel will receive messages sent on this Sender.

use tokio::sync::watch;

#[tokio::main]
async fn main() {
    let (tx, _rx) = watch::channel(0u64);

    tx.send(5).unwrap();

    let rx = tx.subscribe();
    assert_eq!(5, *rx.borrow());

    tx.send(10).unwrap();
    assert_eq!(10, *rx.borrow());
}

The most recent message is considered seen by the channel, so this test is guaranteed to pass.

use tokio::sync::watch;
use tokio::time::Duration;

#[tokio::main]
async fn main() {
    let (tx, _rx) = watch::channel(0u64);
    tx.send(5).unwrap();
    let mut rx = tx.subscribe();

    tokio::spawn(async move {
        // by spawning and sleeping, the message is sent after `main`
        // hits the call to `changed`.
        tokio::time::sleep(Duration::from_millis(10)).await;
        tx.send(100).unwrap();
    });

    rx.changed().await.unwrap();
    assert_eq!(100, *rx.borrow());
}

Returns the number of receivers that currently exist.

Examples
use tokio::sync::watch;

#[tokio::main]
async fn main() {
    let (tx, rx1) = watch::channel("hello");

    assert_eq!(1, tx.receiver_count());

    let mut _rx2 = rx1.clone();

    assert_eq!(2, tx.receiver_count());
}

Trait Implementations

Formats the value using the given formatter. Read more

Executes the destructor for this type. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.