Function timeout

pub fn timeout<F>(
    duration: Duration,
    future: F,
) -> Timeout<<F as IntoFuture>::IntoFuture> 
where
    F: IntoFuture,

Requires a Future to complete before the specified duration has elapsed.

If the future completes before the duration has elapsed, then the completed value is returned. Otherwise, an error is returned and the future is canceled.

Note that the timeout is checked before polling the future, so if the future does not yield during execution then it is possible for the future to complete and exceed the timeout without returning an error.

This function returns a future whose return type is Result<T,Elapsed>, where T is the return type of the provided future.

If the provided future completes immediately, then the future returned from this function is guaranteed to complete immediately with an Ok variant no matter the provided duration.

Cancellation

Cancelling a timeout is done by dropping the future. No additional cleanup or other work is required.

The original future may be obtained by calling Timeout::into_inner. This consumes the Timeout.

Examples

Create a new Timeout set to expire in 10 milliseconds.

use tokio::time::timeout;
use tokio::sync::oneshot;

use std::time::Duration;

let (tx, rx) = oneshot::channel();

// Wrap the future with a `Timeout` set to expire in 10 milliseconds.
if let Err(_) = timeout(Duration::from_millis(10), rx).await {
    println!("did not receive value within 10 ms");
}

Panics

This function panics if there is no current timer set.

It can be triggered when Builder::enable_time or Builder::enable_all are not included in the builder.

It can also panic whenever a timer is created outside of a Tokio runtime. That is why rt.block_on(sleep(...)) will panic, since the function is executed outside of the runtime. Whereas rt.block_on(async {sleep(...).await}) doesn’t panic. And this is because wrapping the function on an async makes it lazy, and so gets executed inside the runtime successfully without panicking.