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Clarify platform specific resolution in sleep function docs #4474

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merged 3 commits into from Apr 6, 2022
Merged

Clarify platform specific resolution in sleep function docs #4474

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b2c8f4f
Clarify platform specific resolution in sleep function docs
jbuckmccready Feb 5, 2022
310af93
Update tokio/src/time/driver/sleep.rs
Darksonn Mar 16, 2022
4269b9d
Merge branch 'master' into sleep_resolution_doc
Darksonn Mar 16, 2022
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4 changes: 3 additions & 1 deletion tokio/src/time/driver/sleep.rs
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Expand Up @@ -72,7 +72,9 @@ pub fn sleep_until(deadline: Instant) -> 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.
/// require high-resolution timers. The implementation is platform specific
/// such that the actual resolution may be greater than 1 millisecond and vary
/// between platforms.
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I would like this to be more specific if possible.

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Should the docs define the behavior to be expected for each supported platform based on the current implementation ( think it would just link the mio docs)? I found a few issues about the timer granularity/precision, but none that describe configuring on windows:
#367
#970

Both those issues lead to a solution using this crate: https://github.com/DoumanAsh/async-timer

Poking around the code a little bit I found the code for the buckets and see why the granularity is limited to 1ms by the tokio runtime. And it looks like the ~16ms resolution for windows comes from the OS events implementation in mio, from the mio docs it states IOCP is used to communicate with Windows which I think is what limits the resolution. The async-timer crate creates a timer directly using a different windows API call.

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I remember seeing some issue that mentions a call you can make on windows that makes the IOCP timer more precise, but I can't find it...

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///
/// To run something regularly on a schedule, see [`interval`].
///
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