Module tokio::time

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Expand description

Utilities for tracking time.

This module provides a number of types for executing code after a set period of time.

Delay is a future that does no work and completes at a specific Instant in time.
Interval is a stream yielding a value at a fixed period. It is initialized with a Duration and repeatedly yields each time the duration elapses.
Timeout: Wraps a future or stream, setting an upper bound to the amount of time it is allowed to execute. If the future or stream does not complete in time, then it is canceled and an error is returned.
DelayQueue: A queue where items are returned once the requested delay has expired.

These types are sufficient for handling a large number of scenarios involving time.

These types must be used from within the context of the Runtime.

Examples

Wait 100ms and print “100 ms have elapsed”

use tokio::time::delay_for;

use std::time::Duration;


#[tokio::main]
async fn main() {
    delay_for(Duration::from_millis(100)).await;
    println!("100 ms have elapsed");
}

Require that an operation takes no more than 300ms. Note that this uses the timeout function on the FutureExt trait. This trait is included in the prelude.

use tokio::time::{timeout, Duration};

async fn long_future() {
    // do work here
}

let res = timeout(Duration::from_secs(1), long_future()).await;

if res.is_err() {
    println!("operation timed out");
}

A simple example using interval to execute a task every two seconds.

The difference between interval and delay_for is that an interval measures the time since the last tick, which means that .tick().await may wait for a shorter time than the duration specified for the interval if some time has passed between calls to .tick().await.

If the tick in the example below was replaced with delay_for, the task would only be executed once every three seconds, and not every two seconds.

use tokio::time;

async fn task_that_takes_a_second() {
    println!("hello");
    time::delay_for(time::Duration::from_secs(1)).await
}

#[tokio::main]
async fn main() {
    let mut interval = time::interval(time::Duration::from_secs(2));
    for _i in 0..5 {
        interval.tick().await;
        task_that_takes_a_second().await;
    }
}