Enum MissedTickBehavior

Variants

Burst

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 Instants that 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:

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

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:

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;
# }

Skip

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:

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;
# }