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.
Modules
- Watch error types.
Structs
- Receives values from the associated
Sender
. - Returns a reference to the inner value.
- Sends values to the associated
Receiver
.
Functions
- Creates a new watch channel, returning the “send” and “receive” handles.