[Scheduler] Always yield to native macro tasks when a virtual task completes #31787
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| @@ -241,6 +244,12 @@ function workLoop(initialTime: number) { | |||
| pop(taskQueue); | |||
| } | |||
| currentTask = peek(taskQueue); | |||
| if (enableAlwaysYieldScheduler) { | |||
| if (currentTask === null || currentTask.expirationTime > currentTime) { | |||
| // This currentTask hasn't expired we yield to the browser task. | |||
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We can't really rely on this once we switch to postTask. React already doesn't rely on this because of batching + Suspense, we have our own expiration times that switch to using the microtask queue once the time has elapsed.
So this is really just for anything at Meta that relies on the starvation protection. Maybe once this lands, that could be its own flag, too, and then Meta can try rolling it out to see what happens.
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…mpletes (#31787) As an alternative to #31784. We should really just always yield each virtual task to a native task. So that it's 1:1 with native tasks. This affects when microtasks within each task happens. This brings us closer to native `postTask` semantics which makes it more seamless to just use that when available. This still doesn't yield when a task expires to protect against starvation. DiffTrain build for [f5077bc](f5077bc)
This was referenced Dec 18, 2024
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#31787 introduces an experimental scheduler flag: `enableAlwaysYieldScheduler`, which is turned off for www. There wasn't a SchedulerFeatureFlags fork for native-fb, so the experimental change was enabled in the Scheduler-dev build there which causes test failures and is blocking the sync. #31805 introduces another scheduler flag `enableRequestPaint`, which is set as a `__VARIANT__` on www. I've set this to `true` here to preserve the existing behavior. We can follow up with dynamic flags for native-fb after unblocking the sync.
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#31787 introduces an experimental scheduler flag: `enableAlwaysYieldScheduler`, which is turned off for www. There wasn't a SchedulerFeatureFlags fork for native-fb, so the experimental change was enabled in the Scheduler-dev build there which causes test failures and is blocking the sync. #31805 introduces another scheduler flag `enableRequestPaint`, which is set as a `__VARIANT__` on www. I've set this to `true` here to preserve the existing behavior. We can follow up with dynamic flags for native-fb after unblocking the sync. DiffTrain build for [bd76ce5](bd76ce5)
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As an alternative to #31784.
We should really just always yield each virtual task to a native task. So that it's 1:1 with native tasks. This affects when microtasks within each task happens. This brings us closer to native
postTasksemantics which makes it more seamless to just use that when available.This still doesn't yield when a task expires to protect against starvation.