tokio_timerfd/
delay.rs

1use std::future::Future;
2use std::io::Error as IoError;
3use std::pin::Pin;
4use std::task::{Context, Poll};
5use std::time::Instant;
6
7use crate::{ClockId, TimerFd};
8use futures_core::ready;
9use timerfd::{SetTimeFlags, TimerState};
10use tokio::io::{AsyncRead, ReadBuf};
11
12/// A future that completes at a specified instant in time.
13/// Instances of Delay perform no work and complete with () once the specified deadline has been reached.
14/// Delay is powered by `timerfd` and has a resolution of 1 nanosecond.
15pub struct Delay {
16    timerfd: TimerFd,
17    deadline: Instant,
18    initialized: bool,
19}
20
21impl Delay {
22    /// Create a new `Delay` instance that elapses at `deadline`.
23    pub fn new(deadline: Instant) -> Result<Self, IoError> {
24        let timerfd = TimerFd::new(ClockId::Monotonic)?;
25        Ok(Delay {
26            timerfd,
27            deadline,
28            initialized: false,
29        })
30    }
31
32    /// Returns the instant at which the future will complete.
33    pub fn deadline(&self) -> Instant {
34        self.deadline
35    }
36
37    /// Returns true if the `Delay` has elapsed
38    pub fn is_elapsed(&self) -> bool {
39        self.deadline > Instant::now()
40    }
41
42    /// Reset the `Delay` instance to a new deadline.
43    pub fn reset(&mut self, deadline: Instant) {
44        self.deadline = deadline;
45        self.initialized = false;
46    }
47}
48
49impl Future for Delay {
50    type Output = Result<(), IoError>;
51
52    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
53        if !self.initialized {
54            let now = Instant::now();
55            let duration = if self.deadline > now {
56                self.deadline - now
57            } else {
58                return Poll::Ready(Ok(()));
59            };
60            self.timerfd
61                .set_state(TimerState::Oneshot(duration), SetTimeFlags::Default);
62            self.initialized = true;
63        }
64        let mut buf = [0u8; 8];
65        let mut buf = ReadBuf::new(&mut buf);
66        ready!(Pin::new(&mut self.as_mut().timerfd).poll_read(cx, &mut buf)?);
67        Poll::Ready(Ok(()))
68    }
69}
70
71#[cfg(test)]
72mod tests {
73    use super::*;
74    use std::time::{Duration, Instant};
75
76    #[tokio::test]
77    async fn delay_zero_duration() -> Result<(), std::io::Error> {
78        let now = Instant::now();
79        let delay = Delay::new(Instant::now())?;
80        delay.await?;
81        let elapsed = now.elapsed();
82        println!("{:?}", elapsed);
83        assert!(elapsed < Duration::from_millis(1));
84        Ok(())
85    }
86
87    #[tokio::test]
88    async fn delay_works() {
89        let now = Instant::now();
90        let delay = Delay::new(now + Duration::from_micros(10)).unwrap();
91        delay.await.unwrap();
92        let elapsed = now.elapsed();
93        println!("{:?}", elapsed);
94        assert!(elapsed < Duration::from_millis(1));
95    }
96}
tokio_timerfd/delay.rs

tokio_timerfd/
delay.rs
