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

use crate::time::driver::{Handle, TimerEntry};
use crate::time::{error::Error, Duration, Instant};

use pin_project_lite::pin_project;
use std::future::Future;
use std::pin::Pin;
use std::task::{self, Poll};

/// Waits until `deadline` is reached.
///
/// No work is performed while awaiting on the sleep future to complete. `Sleep`
/// operates at millisecond granularity and should not be used for tasks that
/// require high-resolution timers.
///
/// # Cancellation
///
/// Canceling a sleep instance is done by dropping the returned future. No additional
/// cleanup work is required.
pub fn sleep_until(deadline: Instant) -> Sleep {
    Sleep::new_timeout(deadline)
}

/// Waits until `duration` has elapsed.
///
/// Equivalent to `sleep_until(Instant::now() + duration)`. An asynchronous
/// analog to `std::thread::sleep`.
///
/// No work is performed while awaiting on the sleep future to complete. `Sleep`
/// operates at millisecond granularity and should not be used for tasks that
/// require high-resolution timers.
///
/// To run something regularly on a schedule, see [`interval`].
///
/// The maximum duration for a sleep is 68719476734 milliseconds (approximately 2.2 years).
///
/// # Cancellation
///
/// Canceling a sleep instance is done by dropping the returned future. No additional
/// cleanup work is required.
///
/// # Examples
///
/// Wait 100ms and print "100 ms have elapsed".
///
/// ```
/// use tokio::time::{sleep, Duration};
///
/// #[tokio::main]
/// async fn main() {
///     sleep(Duration::from_millis(100)).await;
///     println!("100 ms have elapsed");
/// }
/// ```
///
/// [`interval`]: crate::time::interval()
pub fn sleep(duration: Duration) -> Sleep {
    sleep_until(Instant::now() + duration)
}

pin_project! {
    /// Future returned by [`sleep`](sleep) and
    /// [`sleep_until`](sleep_until).
    #[derive(Debug)]
    #[must_use = "futures do nothing unless you `.await` or poll them"]
    pub struct Sleep {
        deadline: Instant,

        // The link between the `Sleep` instance and the timer that drives it.
        #[pin]
        entry: TimerEntry,
    }
}

impl Sleep {
    pub(crate) fn new_timeout(deadline: Instant) -> Sleep {
        let handle = Handle::current();
        let entry = TimerEntry::new(&handle, deadline);

        Sleep { deadline, entry }
    }

    /// Returns the instant at which the future will complete.
    pub fn deadline(&self) -> Instant {
        self.deadline
    }

    /// Returns `true` if `Sleep` has elapsed.
    ///
    /// A `Sleep` instance is elapsed when the requested duration has elapsed.
    pub fn is_elapsed(&self) -> bool {
        self.entry.is_elapsed()
    }

    /// Resets the `Sleep` instance to a new deadline.
    ///
    /// Calling this function allows changing the instant at which the `Sleep`
    /// future completes without having to create new associated state.
    ///
    /// This function can be called both before and after the future has
    /// completed.
    pub fn reset(self: Pin<&mut Self>, deadline: Instant) {
        let me = self.project();
        me.entry.reset(deadline);
        *me.deadline = deadline;
    }

    fn poll_elapsed(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Result<(), Error>> {
        let me = self.project();

        // Keep track of task budget
        let coop = ready!(crate::coop::poll_proceed(cx));

        me.entry.poll_elapsed(cx).map(move |r| {
            coop.made_progress();
            r
        })
    }
}

impl Future for Sleep {
    type Output = ();

    fn poll(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
        // `poll_elapsed` can return an error in two cases:
        //
        // - AtCapacity: this is a pathological case where far too many
        //   sleep instances have been scheduled.
        // - Shutdown: No timer has been setup, which is a mis-use error.
        //
        // Both cases are extremely rare, and pretty accurately fit into
        // "logic errors", so we just panic in this case. A user couldn't
        // really do much better if we passed the error onwards.
        match ready!(self.as_mut().poll_elapsed(cx)) {
            Ok(()) => Poll::Ready(()),
            Err(e) => panic!("timer error: {}", e),
        }
    }
}