# [−] [src] Module tokio::time

Utilities for tracking time.

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

- `Sleep` 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.

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::sleep;

    use std::time::Duration;

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

Require that an operation takes no more than 300ms.

    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 `sleep` 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 `sleep`, 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::sleep(time::Duration::from_secs(1)).await
    }

    #[tokio::main]
    async fn main() {
        let interval = time::interval(time::Duration::from_secs(2));
        tokio::pin!(interval);

        for _i in 0..5 {
            interval.as_mut().tick().await;
            task_that_takes_a_second().await;
        }
    }

## Re-exports

`pub use std::time::Duration;`

## Modules

error | Time error types.

## Structs

Instant | A measurement of a monotonically nondecreasing clock. Opaque and useful only with `Duration`.
Interval | Stream returned by `interval` and `interval_at`.
Sleep | Future returned by `sleep` and `sleep_until`.
Timeout | Future returned by `timeout` and `timeout_at`.

## Functions

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`.
sleep | Waits until `duration` has elapsed.
sleep_until | Waits until `deadline` is reached.
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.