Expand description
A single-producer, multi-consumer channel that only retains the last sent value.
This channel is useful for watching for changes to a value from multiple points in the code base, for example, changes to configuration values.
Usage
channel returns a Sender / Receiver pair. These are the producer
and consumer halves of the channel. The channel is created with an initial
value. The latest value stored in the channel is accessed with
Receiver::borrow(). Awaiting Receiver::changed() waits for a new
value to be sent by the Sender half.
Examples
use tokio::sync::watch;
let (tx, mut rx) = watch::channel("hello");
tokio::spawn(async move {
while rx.changed().await.is_ok() {
println!("received = {:?}", *rx.borrow());
}
});
tx.send("world")?;Closing
Sender::is_closed and Sender::closed allow the producer to detect
when all Receiver handles have been dropped. This indicates that there
is no further interest in the values being produced and work can be stopped.
The value in the channel will not be dropped until the sender and all receivers have been dropped.
Thread safety
Both Sender and Receiver are thread safe. They can be moved to other
threads and can be used in a concurrent environment. Clones of Receiver
handles may be moved to separate threads and also used concurrently.