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Add jitter support to recurring tasks #2542

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merged 9 commits into from
Oct 13, 2023
Merged

Add jitter support to recurring tasks #2542

merged 9 commits into from
Oct 13, 2023

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LorenzoFritzsch
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@LorenzoFritzsch LorenzoFritzsch commented Oct 9, 2023 •
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Add jitter support to functions managing recurring tasks.

Motivation:

Closes #2505.

Modifications:

Overloaded the following EventLoop functions that might need jitter support:

  • flatScheduleTask
  • scheduleRepeatedTask
  • scheduleRepeatedAsyncTask

with the following new parameter: maximumAllowableJitter: TimeAmount, which is the exclusive upper bound of the jitter range that will be added to the delay and initialDelay parameters.

Result:

If jitter is needed when scheduling a repeated task with one of the functions listed above, it will be possible to add it by using the maximumAllowableJitter parameter.

@LorenzoFritzsch LorenzoFritzsch changed the title Add jitter support - Issue #2505 Add jitter support Oct 9, 2023
Lukasa
Lukasa requested changes Oct 10, 2023
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Thanks, this code looks broadly correct! Can we add some unit tests to validate their correct behaviour? EmbeddedEventLoop will be useful for this as it has a fake clock.

Sources/NIOCore/EventLoop.swift Outdated
@discardableResult
@inlinable
@preconcurrency
public func flatScheduleTask<T>(
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Can we also add an extension that offers a variation of scheduleTask with jitter?

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A function that schedules a task after a given amount of time, with that amount being jittered? If this is the case I don't see the difference with this overloaded function, and as you pointed out as there's no rescheduling jittering should be unnecessary.

Sources/NIOCore/EventLoop.swift Outdated
/// Schedule a `task` that is executed by this `EventLoop` after the given amount of time.
///
/// - parameters:
/// - delay: The delay between the end of one task and the start of the next.
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This seems wrong, as flatScheduleTask doesn't reschedule anything.

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I misunderstood the nature of this function, I will remove this overload as it's unnecessary.

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Sure, if we remove this overload then that's fine.

Sources/NIOCore/EventLoop.swift Outdated
/// - note: You can only cancel a task before it has started executing.
@discardableResult
@inlinable
@preconcurrency
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This is not @preconcurrency.

Sources/NIOCore/EventLoop.swift Outdated
_ task: @escaping @Sendable (RepeatedTask) throws -> Void
) -> RepeatedTask {
let jitteredDelay = self._getJitteredDelay(delay: delay, maximumAllowableJitter: maximumAllowableJitter)
return self.scheduleRepeatedTask(initialDelay: initialDelay, delay: jitteredDelay, notifying: promise, task)
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Should we jitter the initial delay as well?

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Yes will do, jittering the initial delay will avoid a first load spike, which is part of what this PR should fix

Lukasa
Lukasa reviewed Oct 12, 2023
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Looking great, just a quick note.

Sources/NIOCore/EventLoop.swift Outdated
/// - task: The closure that will be executed.
/// - return: `RepeatedTask`
@discardableResult
@preconcurrency
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We can remove the @preconcurrency annotations here, these functions are new.

Sources/NIOCore/EventLoop.swift Outdated
///
/// - return: `RepeatedTask`
@discardableResult
@preconcurrency
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Same preconcurrency note here.

@LorenzoFritzsch LorenzoFritzsch changed the title Add jitter support Add jitter support to recurring tasks Oct 12, 2023
Lukasa
Lukasa approved these changes Oct 12, 2023
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Nice one, LGTM.

@Lukasa Lukasa added the 🆕 semver/minor Adds new public API. label Oct 12, 2023
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Lukasa commented Oct 12, 2023

@swift-server-bot test this please

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Lukasa commented Oct 12, 2023

Couple of build errors need to be cleaned up I'm afraid:

18:28:18 /swift-nio/Tests/NIOPosixTests/EventLoopTest.swift:394:13: error: mutation of captured var 'sentinel' in concurrently-executing code
18:28:18             sentinel += 1
18:28:18             ^
18:28:18 /swift-nio/Tests/NIOPosixTests/EventLoopTest.swift:846:13: error: mutation of captured var 'sentinel' in concurrently-executing code
18:28:18             sentinel += 1
18:28:18             ^

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@swift-server-bot test this please

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Lukasa commented Oct 13, 2023

@swift-server-bot test this please

@Lukasa Lukasa merged commit 7954dba into apple:main Oct 13, 2023
@LorenzoFritzsch LorenzoFritzsch deleted the 2505-jitter-support branch October 14, 2023 10:40
LorenzoFritzsch added a commit to LorenzoFritzsch/swift-nio that referenced this pull request Oct 14, 2023
@LorenzoFritzsch
Merge pull request #2 from apple/main
1ef3c42 
Add jitter support to recurring tasks (apple#2542)
@0xTim 0xTim mentioned this pull request Jan 16, 2025
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@0xTim 0xTim mentioned this pull request Feb 23, 2025
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schedule(Repeated)(Async)Task (and friends): jitter support
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@LorenzoFritzsch @Lukasa