Don't rely on Scheduler.didTimeout to tell us that SyncBatched is synchronous #19469
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Tasks with SyncBatchedPriority — used by Blocking Mode — should always be rendered by the `peformSyncWorkOnRoot` path, not `performConcurrentWorkOnRoot`. Currently, they go through the `performConcurrentWorkOnRoot` callback. Then, we check `didTimeout` to see if the task expired. Since SyncBatchedPriority translates to ImmediatePriority in the Scheduler, `didTimeout` is always `true`, so we mark it as expired. Then it exits and re-enters in the `performSyncWorkOnRoot` path. Aside from being overly convoluted, we shouldn't rely on Scheduler to tell us that SyncBatchedPriority work is synchronous. We should handle that ourselves. This will allow us to remove the `didTimeout` check. And it further decouples us from the Scheduler priority, so we can eventually remove that, too.
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rickhanlonii
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Jul 27, 2020
| performSyncWorkOnRoot.bind(null, root), | ||
| ); | ||
| } else if (newCallbackPriority === SyncBatchedLanePriority) { | ||
| newCallbackNode = scheduleCallback( |
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Are we intentionally not using scheduleSyncCallback like in the block above?
What if other sync work is already scheduled, do we want this to always come after?
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The naming is confusing. scheduleSyncCallback adds stuff to a special queue that can be flushed synchronously without going through Scheduler. It's used for SyncLane and expired updates.
"sync" in performSyncWorkOnRoot means that it doesn't yield to the main thread and it doesn't check Suspense timeouts (though that part might change), so it has fewer checks than concurrent updates.
SyncBatched is kind of a mix between sync mode and concurrent mode. It doesn't yield to the main thread, but it does go through Scheduler (i.e. is scheduled by postMessage), hence the weird naming conflicts.
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I see, thanks for explaining 👍
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Tasks with SyncBatchedPriority — used by Blocking Mode — should always be rendered by the
performSyncWorkOnRootpath, notperformConcurrentWorkOnRoot.Currently, they go through the
performConcurrentWorkOnRootcallback. Then, we checkdidTimeoutto see if the task expired. Since SyncBatchedPriority translates to ImmediatePriority in the Scheduler,didTimeoutis alwaystrue, so we mark it as expired. Then it exits and re-enters in theperformSyncWorkOnRootpath.Aside from being overly convoluted, we shouldn't rely on Scheduler to tell us that SyncBatchedPriority work is synchronous. We should handle that ourselves.
This will allow us to remove the
didTimeoutcheck. And it further decouples us from the Scheduler priority, so we can eventually remove that, too.