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use crate::future::poll_fn;
use crate::time::{sleep_until, Duration, Instant, Sleep};
use crate::util::trace;
use std::future::Future;
use std::panic::Location;
use std::pin::Pin;
use std::task::{Context, Poll};
/// Creates new [`Interval`] that yields with interval of `period`. The first
/// tick completes immediately. The default [`MissedTickBehavior`] is
/// [`Burst`](MissedTickBehavior::Burst), but this can be configured
/// by calling [`set_missed_tick_behavior`](Interval::set_missed_tick_behavior).
///
/// 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)`](interval_at).
///
/// # 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; // ticks immediately
/// interval.tick().await; // ticks after 10ms
/// interval.tick().await; // ticks after 10ms
///
/// // 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()
/// [`.tick().await`]: Interval::tick
#[track_caller]
pub fn interval(period: Duration) -> Interval {
assert!(period > Duration::new(0, 0), "`period` must be non-zero.");
internal_interval_at(Instant::now(), period, trace::caller_location())
}
/// Creates new [`Interval`] that yields with interval of `period` with the
/// first tick completing at `start`. The default [`MissedTickBehavior`] is
/// [`Burst`](MissedTickBehavior::Burst), but this can be configured
/// by calling [`set_missed_tick_behavior`](Interval::set_missed_tick_behavior).
///
/// 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; // ticks after 50ms
/// interval.tick().await; // ticks after 10ms
/// interval.tick().await; // ticks after 10ms
///
/// // approximately 70ms have elapsed.
/// }
/// ```
#[track_caller]
pub fn interval_at(start: Instant, period: Duration) -> Interval {
assert!(period > Duration::new(0, 0), "`period` must be non-zero.");
internal_interval_at(start, period, trace::caller_location())
}
#[cfg_attr(not(all(tokio_unstable, feature = "tracing")), allow(unused_variables))]
fn internal_interval_at(
start: Instant,
period: Duration,
location: Option<&'static Location<'static>>,
) -> Interval {
#[cfg(all(tokio_unstable, feature = "tracing"))]
let resource_span = {
let location = location.expect("should have location if tracing");
tracing::trace_span!(
"runtime.resource",
concrete_type = "Interval",
kind = "timer",
loc.file = location.file(),
loc.line = location.line(),
loc.col = location.column(),
)
};
#[cfg(all(tokio_unstable, feature = "tracing"))]
let delay = resource_span.in_scope(|| Box::pin(sleep_until(start)));
#[cfg(not(all(tokio_unstable, feature = "tracing")))]
let delay = Box::pin(sleep_until(start));
Interval {
delay,
period,
missed_tick_behavior: Default::default(),
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span,
}
}
/// Defines the behavior of an [`Interval`] when it misses a tick.
///
/// Sometimes, an [`Interval`]'s tick is missed. For example, consider the
/// following:
///
/// ```
/// use tokio::time::{self, Duration};
/// # async fn task_that_takes_one_to_three_millis() {}
///
/// #[tokio::main]
/// async fn main() {
/// // ticks every 2 milliseconds
/// let mut interval = time::interval(Duration::from_millis(2));
/// for _ in 0..5 {
/// interval.tick().await;
/// // if this takes more than 2 milliseconds, a tick will be delayed
/// task_that_takes_one_to_three_millis().await;
/// }
/// }
/// ```
///
/// Generally, a tick is missed if too much time is spent without calling
/// [`Interval::tick()`].
///
/// By default, when a tick is missed, [`Interval`] fires ticks as quickly as it
/// can until it is "caught up" in time to where it should be.
/// `MissedTickBehavior` can be used to specify a different behavior for
/// [`Interval`] to exhibit. Each variant represents a different strategy.
///
/// Note that because the executor cannot guarantee exact precision with timers,
/// these strategies will only apply when the delay is greater than 5
/// milliseconds.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum MissedTickBehavior {
/// Ticks as fast as possible until caught up.
///
/// When this strategy is used, [`Interval`] schedules ticks "normally" (the
/// same as it would have if the ticks hadn't been delayed), which results
/// in it firing ticks as fast as possible until it is caught up in time to
/// where it should be. Unlike [`Delay`] and [`Skip`], the ticks yielded
/// when `Burst` is used (the [`Instant`]s that [`tick`](Interval::tick)
/// yields) aren't different than they would have been if a tick had not
/// been missed. Like [`Skip`], and unlike [`Delay`], the ticks may be
/// shortened.
///
/// This looks something like this:
/// ```text
/// Expected ticks: | 1 | 2 | 3 | 4 | 5 | 6 |
/// Actual ticks: | work -----| delay | work | work | work -| work -----|
/// ```
///
/// In code:
///
/// ```
/// use tokio::time::{interval, Duration};
/// # async fn task_that_takes_200_millis() {}
///
/// # #[tokio::main(flavor = "current_thread")]
/// # async fn main() {
/// let mut interval = interval(Duration::from_millis(50));
///
/// // First tick resolves immediately after creation
/// interval.tick().await;
///
/// task_that_takes_200_millis().await;
/// // The `Interval` has missed a tick
///
/// // Since we have exceeded our timeout, this will resolve immediately
/// interval.tick().await;
///
/// // Since we are more than 100ms after the start of `interval`, this will
/// // also resolve immediately.
/// interval.tick().await;
///
/// // Also resolves immediately, because it was supposed to resolve at
/// // 150ms after the start of `interval`
/// interval.tick().await;
///
/// // Resolves immediately
/// interval.tick().await;
///
/// // Since we have gotten to 200ms after the start of `interval`, this
/// // will resolve after 50ms
/// interval.tick().await;
/// # }
/// ```
///
/// This is the default behavior when [`Interval`] is created with
/// [`interval`] and [`interval_at`].
///
/// [`Delay`]: MissedTickBehavior::Delay
/// [`Skip`]: MissedTickBehavior::Skip
Burst,
/// Tick at multiples of `period` from when [`tick`] was called, rather than
/// from `start`.
///
/// When this strategy is used and [`Interval`] has missed a tick, instead
/// of scheduling ticks to fire at multiples of `period` from `start` (the
/// time when the first tick was fired), it schedules all future ticks to
/// happen at a regular `period` from the point when [`tick`] was called.
/// Unlike [`Burst`] and [`Skip`], ticks are not shortened, and they aren't
/// guaranteed to happen at a multiple of `period` from `start` any longer.
///
/// This looks something like this:
/// ```text
/// Expected ticks: | 1 | 2 | 3 | 4 | 5 | 6 |
/// Actual ticks: | work -----| delay | work -----| work -----| work -----|
/// ```
///
/// In code:
///
/// ```
/// use tokio::time::{interval, Duration, MissedTickBehavior};
/// # async fn task_that_takes_more_than_50_millis() {}
///
/// # #[tokio::main(flavor = "current_thread")]
/// # async fn main() {
/// let mut interval = interval(Duration::from_millis(50));
/// interval.set_missed_tick_behavior(MissedTickBehavior::Delay);
///
/// task_that_takes_more_than_50_millis().await;
/// // The `Interval` has missed a tick
///
/// // Since we have exceeded our timeout, this will resolve immediately
/// interval.tick().await;
///
/// // But this one, rather than also resolving immediately, as might happen
/// // with the `Burst` or `Skip` behaviors, will not resolve until
/// // 50ms after the call to `tick` up above. That is, in `tick`, when we
/// // recognize that we missed a tick, we schedule the next tick to happen
/// // 50ms (or whatever the `period` is) from right then, not from when
/// // were *supposed* to tick
/// interval.tick().await;
/// # }
/// ```
///
/// [`Burst`]: MissedTickBehavior::Burst
/// [`Skip`]: MissedTickBehavior::Skip
/// [`tick`]: Interval::tick
Delay,
/// Skips missed ticks and tick on the next multiple of `period` from
/// `start`.
///
/// When this strategy is used, [`Interval`] schedules the next tick to fire
/// at the next-closest tick that is a multiple of `period` away from
/// `start` (the point where [`Interval`] first ticked). Like [`Burst`], all
/// ticks remain multiples of `period` away from `start`, but unlike
/// [`Burst`], the ticks may not be *one* multiple of `period` away from the
/// last tick. Like [`Delay`], the ticks are no longer the same as they
/// would have been if ticks had not been missed, but unlike [`Delay`], and
/// like [`Burst`], the ticks may be shortened to be less than one `period`
/// away from each other.
///
/// This looks something like this:
/// ```text
/// Expected ticks: | 1 | 2 | 3 | 4 | 5 | 6 |
/// Actual ticks: | work -----| delay | work ---| work -----| work -----|
/// ```
///
/// In code:
///
/// ```
/// use tokio::time::{interval, Duration, MissedTickBehavior};
/// # async fn task_that_takes_75_millis() {}
///
/// # #[tokio::main(flavor = "current_thread")]
/// # async fn main() {
/// let mut interval = interval(Duration::from_millis(50));
/// interval.set_missed_tick_behavior(MissedTickBehavior::Skip);
///
/// task_that_takes_75_millis().await;
/// // The `Interval` has missed a tick
///
/// // Since we have exceeded our timeout, this will resolve immediately
/// interval.tick().await;
///
/// // This one will resolve after 25ms, 100ms after the start of
/// // `interval`, which is the closest multiple of `period` from the start
/// // of `interval` after the call to `tick` up above.
/// interval.tick().await;
/// # }
/// ```
///
/// [`Burst`]: MissedTickBehavior::Burst
/// [`Delay`]: MissedTickBehavior::Delay
Skip,
}
impl MissedTickBehavior {
/// If a tick is missed, this method is called to determine when the next tick should happen.
fn next_timeout(&self, timeout: Instant, now: Instant, period: Duration) -> Instant {
match self {
Self::Burst => timeout + period,
Self::Delay => now + period,
Self::Skip => {
now + period
- Duration::from_nanos(
((now - timeout).as_nanos() % period.as_nanos())
.try_into()
// This operation is practically guaranteed not to
// fail, as in order for it to fail, `period` would
// have to be longer than `now - timeout`, and both
// would have to be longer than 584 years.
//
// If it did fail, there's not a good way to pass
// the error along to the user, so we just panic.
.expect(
"too much time has elapsed since the interval was supposed to tick",
),
)
}
}
}
}
impl Default for MissedTickBehavior {
/// Returns [`MissedTickBehavior::Burst`].
///
/// For most usecases, the [`Burst`] strategy is what is desired.
/// Additionally, to preserve backwards compatibility, the [`Burst`]
/// strategy must be the default. For these reasons,
/// [`MissedTickBehavior::Burst`] is the default for [`MissedTickBehavior`].
/// See [`Burst`] for more details.
///
/// [`Burst`]: MissedTickBehavior::Burst
fn default() -> Self {
Self::Burst
}
}
/// Interval returned by [`interval`] and [`interval_at`].
///
/// This type allows you to wait on a sequence of instants with a certain
/// duration between each instant. Unlike calling [`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/latest/tokio_stream/wrappers/struct.IntervalStream.html
/// [`sleep`]: crate::time::sleep()
#[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,
/// The strategy `Interval` should use when a tick is missed.
missed_tick_behavior: MissedTickBehavior,
#[cfg(all(tokio_unstable, feature = "tracing"))]
resource_span: tracing::Span,
}
impl Interval {
/// Completes when the next instant in the interval has been reached.
///
/// # Cancel safety
///
/// This method is cancellation safe. If `tick` is used as the branch in a `tokio::select!` and
/// another branch completes first, then no tick has been consumed.
///
/// # 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;
/// // approximately 0ms have elapsed. The first tick completes immediately.
/// interval.tick().await;
/// interval.tick().await;
///
/// // approximately 20ms have elapsed.
/// }
/// ```
pub async fn tick(&mut self) -> Instant {
#[cfg(all(tokio_unstable, feature = "tracing"))]
let resource_span = self.resource_span.clone();
#[cfg(all(tokio_unstable, feature = "tracing"))]
let instant = trace::async_op(
|| poll_fn(|cx| self.poll_tick(cx)),
resource_span,
"Interval::tick",
"poll_tick",
false,
);
#[cfg(not(all(tokio_unstable, feature = "tracing")))]
let instant = poll_fn(|cx| self.poll_tick(cx));
instant.await
}
/// Polls 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`](std::task::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 time when we were scheduled to tick
let timeout = self.delay.deadline();
let now = Instant::now();
// If a tick was not missed, and thus we are being called before the
// next tick is due, just schedule the next tick normally, one `period`
// after `timeout`
//
// However, if a tick took excessively long and we are now behind,
// schedule the next tick according to how the user specified with
// `MissedTickBehavior`
let next = if now > timeout + Duration::from_millis(5) {
self.missed_tick_behavior
.next_timeout(timeout, now, self.period)
} else {
timeout + self.period
};
// When we arrive here, the internal delay returned `Poll::Ready`.
// Reset the delay but do not register it. It should be registered with
// the next call to [`poll_tick`].
self.delay.as_mut().reset_without_reregister(next);
// Return the time when we were scheduled to tick
Poll::Ready(timeout)
}
/// Resets the interval to complete one period after the current time.
///
/// This method ignores [`MissedTickBehavior`] strategy.
///
/// # Examples
///
/// ```
/// use tokio::time;
///
/// use std::time::Duration;
///
/// #[tokio::main]
/// async fn main() {
/// let mut interval = time::interval(Duration::from_millis(100));
///
/// interval.tick().await;
///
/// time::sleep(Duration::from_millis(50)).await;
/// interval.reset();
///
/// interval.tick().await;
/// interval.tick().await;
///
/// // approximately 250ms have elapsed.
/// }
/// ```
pub fn reset(&mut self) {
self.delay.as_mut().reset(Instant::now() + self.period);
}
/// Returns the [`MissedTickBehavior`] strategy currently being used.
pub fn missed_tick_behavior(&self) -> MissedTickBehavior {
self.missed_tick_behavior
}
/// Sets the [`MissedTickBehavior`] strategy that should be used.
pub fn set_missed_tick_behavior(&mut self, behavior: MissedTickBehavior) {
self.missed_tick_behavior = behavior;
}
/// Returns the period of the interval.
pub fn period(&self) -> Duration {
self.period
}
}