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
|
use crate::time::driver::Registration;
use crate::time::{Duration, Instant};
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 delay to complete. The delay
/// operates at millisecond granularity and should not be used for tasks that
/// require high-resolution timers.
///
/// # Cancellation
///
/// Canceling a delay is done by dropping the returned future. No additional
/// cleanup work is required.
pub fn delay_until(deadline: Instant) -> Delay {
let registration = Registration::new(deadline, Duration::from_millis(0));
Delay { registration }
}
/// Waits until `duration` has elapsed.
///
/// Equivalent to `delay_until(Instant::now() + duration)`. An asynchronous
/// analog to `std::thread::sleep`.
///
/// No work is performed while awaiting on the delay to complete. The delay
/// 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`].
///
/// # Cancellation
///
/// Canceling a delay 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::{delay_for, Duration};
///
/// #[tokio::main]
/// async fn main() {
/// delay_for(Duration::from_millis(100)).await;
/// println!("100 ms have elapsed");
/// }
/// ```
///
/// [`interval`]: crate::time::interval()
#[cfg_attr(docsrs, doc(alias = "sleep"))]
pub fn delay_for(duration: Duration) -> Delay {
delay_until(Instant::now() + duration)
}
/// Future returned by [`delay_until`](delay_until) and
/// [`delay_for`](delay_for).
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct Delay {
/// The link between the `Delay` instance and the timer that drives it.
///
/// This also stores the `deadline` value.
registration: Registration,
}
impl Delay {
pub(crate) fn new_timeout(deadline: Instant, duration: Duration) -> Delay {
let registration = Registration::new(deadline, duration);
Delay { registration }
}
/// Returns the instant at which the future will complete.
pub fn deadline(&self) -> Instant {
self.registration.deadline()
}
/// Returns `true` if the `Delay` has elapsed
///
/// A `Delay` is elapsed when the requested duration has elapsed.
pub fn is_elapsed(&self) -> bool {
self.registration.is_elapsed()
}
/// Resets the `Delay` instance to a new deadline.
///
/// Calling this function allows changing the instant at which the `Delay`
/// 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(&mut self, deadline: Instant) {
self.registration.reset(deadline);
}
}
impl Future for Delay {
type Output = ();
fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
// `poll_elapsed` can return an error in two cases:
//
// - AtCapacity: this is a pathlogical case where far too many
// delays 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.registration.poll_elapsed(cx)) {
Ok(()) => Poll::Ready(()),
Err(e) => panic!("timer error: {}", e),
}
}
}
|
