1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
use crate::future::poll_fn;
use crate::time::{sleep_until, Duration, Instant, Sleep};

use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};

/// Creates new `Interval` that yields with interval of `duration`. The first
/// tick completes immediately.
///
/// An interval will tick indefinitely. At any time, the `Interval` value can be
/// dropped. This cancels the interval.
///
/// This function is equivalent to `interval_at(Instant::now(), period)`.
///
/// # Panics
///
/// This function panics if `period` is zero.
///
/// # Examples
///
/// ```
/// use tokio::time::{self, Duration};
///
/// #[tokio::main]
/// async fn main() {
///     let mut interval = time::interval(Duration::from_millis(10));
///
///     interval.tick().await;
///     interval.tick().await;
///     interval.tick().await;
///
///     // approximately 20ms have elapsed.
/// }
/// ```
///
/// 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 mut interval = time::interval(time::Duration::from_secs(2));
///     for _i in 0..5 {
///         interval.tick().await;
///         task_that_takes_a_second().await;
///     }
/// }
/// ```
///
/// [`sleep`]: crate::time::sleep()
pub fn interval(period: Duration) -> Interval {
    assert!(period > Duration::new(0, 0), "`period` must be non-zero.");

    interval_at(Instant::now(), period)
}

/// Creates new `Interval` that yields with interval of `period` with the
/// first tick completing at `start`.
///
/// An interval will tick indefinitely. At any time, the `Interval` value can be
/// dropped. This cancels the interval.
///
/// # Panics
///
/// This function panics if `period` is zero.
///
/// # Examples
///
/// ```
/// use tokio::time::{interval_at, Duration, Instant};
///
/// #[tokio::main]
/// async fn main() {
///     let start = Instant::now() + Duration::from_millis(50);
///     let mut interval = interval_at(start, Duration::from_millis(10));
///
///     interval.tick().await;
///     interval.tick().await;
///     interval.tick().await;
///
///     // approximately 70ms have elapsed.
/// }
/// ```
pub fn interval_at(start: Instant, period: Duration) -> Interval {
    assert!(period > Duration::new(0, 0), "`period` must be non-zero.");

    Interval {
        delay: Box::pin(sleep_until(start)),
        period,
    }
}

/// Interval returned by [`interval`](interval) and [`interval_at`](interval_at).
///
/// This type allows you to wait on a sequence of instants with a certain
/// duration between each instant. Unlike calling [`sleep`](crate::time::sleep)
/// in a loop, this lets you count the time spent between the calls to `sleep`
/// as well.
///
/// An `Interval` can be turned into a `Stream` with [`IntervalStream`].
///
/// [`IntervalStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.IntervalStream.html
#[derive(Debug)]
pub struct Interval {
    /// Future that completes the next time the `Interval` yields a value.
    delay: Pin<Box<Sleep>>,

    /// The duration between values yielded by `Interval`.
    period: Duration,
}

impl Interval {
    /// Completes when the next instant in the interval has been reached.
    ///
    /// # Examples
    ///
    /// ```
    /// use tokio::time;
    ///
    /// use std::time::Duration;
    ///
    /// #[tokio::main]
    /// async fn main() {
    ///     let mut interval = time::interval(Duration::from_millis(10));
    ///
    ///     interval.tick().await;
    ///     interval.tick().await;
    ///     interval.tick().await;
    ///
    ///     // approximately 20ms have elapsed.
    /// }
    /// ```
    pub async fn tick(&mut self) -> Instant {
        poll_fn(|cx| self.poll_tick(cx)).await
    }

    /// Poll for the next instant in the interval to be reached.
    ///
    /// This method can return the following values:
    ///
    ///  * `Poll::Pending` if the next instant has not yet been reached.
    ///  * `Poll::Ready(instant)` if the next instant has been reached.
    ///
    /// When this method returns `Poll::Pending`, the current task is scheduled
    /// to receive a wakeup when the instant has elapsed. Note that on multiple
    /// calls to `poll_tick`, only the `Waker` from the `Context` passed to the
    /// most recent call is scheduled to receive a wakeup.
    pub fn poll_tick(&mut self, cx: &mut Context<'_>) -> Poll<Instant> {
        // Wait for the delay to be done
        ready!(Pin::new(&mut self.delay).poll(cx));

        // Get the `now` by looking at the `delay` deadline
        let now = self.delay.deadline();

        // The next interval value is `duration` after the one that just
        // yielded.
        let next = now + self.period;
        self.delay.as_mut().reset(next);

        // Return the current instant
        Poll::Ready(now)
    }

    /// Returns the period of the interval.
    pub fn period(&self) -> Duration {
        self.period
    }
}