Module tokio::time

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;
    }
}

Modules

delay_queue

A queue of delayed elements.

Structs

Delay	Future returned by delay_until and delay_for.
DelayQueue	A queue of delayed elements.
Duration	A Duration type to represent a span of time, typically used for system timeouts.
Elapsed	Error returned by Timeout.
Error	Errors encountered by the timer implementation.
Instant	A measurement of the system clock, useful for talking to external entities like the file system or other processes.
Interval	Stream returned by interval and interval_at.
Throttle	Stream for the throttle function.
Timeout	Future returned by timeout and timeout_at.

Functions

delay_for	Waits until duration has elapsed.
delay_until	Waits until deadline is reached.
interval	Creates new Interval that yields with interval of duration. The first tick completes immediately.
interval_at	Creates new Interval that yields with interval of period with the first tick completing at start.
throttle	Slows down a stream by enforcing a delay between items. They will be produced not more often than the specified interval.
timeout	Require a Future to complete before the specified duration has elapsed.
timeout_at	Require a Future to complete before the specified instant in time.