feat(shared-runtime)!: use weak waker in trigger [APMSP-3371]#2050
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feat(shared-runtime)!: use weak waker in trigger [APMSP-3371]#2050VianneyRuhlmann wants to merge 7 commits into
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Co-authored-by: paullegranddc <82819397+paullegranddc@users.noreply.github.com>
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yannham
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This solution adds a bit of code but looks more robust than the draining channel/on_pause business, is still reasonable and 👍 for the very clear documentation of the weak_waker module
| /// | ||
| /// See the [module-level documentation](self) for details. | ||
| #[must_use = "futures do nothing unless you `.await` or poll them"] | ||
| pub fn wrap<F: Future>(fut: F) -> WeakWakerFuture<F> { |
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Nit: should this be WeakWakerFuture::new, or at least WeakWakerFuture::wrap instead?
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| pub struct WeakWakerFuture<F: Future> { | ||
| fut: F, | ||
| weak_waker: Option<WeakWaker>, |
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Naive question: isn't there a double Option wrapping here? If AtomicWaker is already morally an Option<Waker>, could we just use WeakWaker here and put "none" in the atomic waker?
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This is an optimisation so that we never allocate a WeakWaker of the Future is never polled. (A race bewteen two futures with one already ready for instance).
The Option doesn't cost anything since WeakWaker is a wrapper over Arc
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You're right I can remove it, it makes the code way more readable. However it means I have to allocate the WeakWaker Arc and the AtomicWaker in new rather than on the first call to poll, but I think it's worth it.
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Ah, there's an Arc in between indeed. Not sure what's the optimal trade-off, I guess it depends if you expect the "no allocation" case to happen often. I personally don't have a strong opinion
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What does this PR do?
Wrap the trigger future waker to use a weak reference on the runtime. This allows the runtime to be dropped and properly shutdown when calling
before_forkMotivation
When reading from a channel in the trigger method, the waker being held by the channel can prevent the tokio driver from being dropped when calling
before_forkwhich can cause crashes in macos as the kqueue handle becomes invalid in the child process.Additional Notes
Anything else we should know when reviewing?
How to test the change?
Describe here in detail how the change can be validated.