Function timeout_at 

pub fn timeout_at<F>(deadline: Instant, future: F) -> Timeout<F::IntoFuture> 
where
    F: IntoFuture,

Available on crate feature time only.

Requires a Future to complete before the specified instant in time.

If the future completes before the instant is reached, then the completed value is returned. Otherwise, an error is returned.

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 deadline.

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::{Instant, timeout_at};
use tokio::sync::oneshot;

use std::time::Duration;

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

// Wrap the future with a `Timeout` set to expire 10 milliseconds into the
// future.
if let Err(_) = timeout_at(Instant::now() + 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.