Get next expiration time from FiberRoot #16678
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A FiberRoot can have pending work at many distinct priorities. (Note: we refer to these levels as "expiration times" to distinguish the concept from Scheduler's notion of priority levels, which represent broad categories of work. React expiration times are more granualar. They're more like a concurrent thread ID, which also happens to correspond to a moment on a timeline. It's an overloaded concept and I'm handwaving over some of the details.) Given a root, there's no convenient way to read all the pending levels in the entire tree, i.e. there's no single queue-like structure that tracks all the levels, because that granularity of information is not needed by our algorithms. Instead we track the subset of information that we actually need — most importantly, the highest priority level that exists in the entire tree. Aside from that, the other information we track includes the range of pending levels that are known to be suspended, and therefore should not be worked on. This is a refactor of how that information is tracked, and what each field represents: - A *pending* level is work that is unfinished, or not yet committed. This includes work that is suspended from committing. `firstPendingTime` and `lastPendingTime` represent the range of pending work. (Previously, "pending" was the same as "not suspended.") - A *suspended* level is work that did not complete because data was missing. `firstSuspendedTime` and `lastSuspendedTime` represent the range of suspended work. It is a subset of the pending range. (These fields are new to this commit.) - `nextAfterSuspendedTime` represents the next known level that comes after the suspended range. This commit doesn't change much in terms of observable behavior. The one change is that, when a level is suspended, React will continue working on the next known level instead of jumping straight to the last pending level. Subsequent commits will use this new structure for a more substantial refactor for how tasks are scheduled per root.
Given a FiberRoot, we should be able to determine the next expiration time that needs to be worked on, taking into account the levels that are pending, suspended, pinged, and so on. This removes the `expirationTime` argument from `scheduleCallbackForRoot`, and renames it to `ensureRootIsScheduled` to reflect the new signature. The expiration time is instead read from the root using a new function, `getNextExpirationTimeToWorkOn`. The next step will be to remove the `expirationTime` argument from `renderRoot`, too.
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sebmarkbage
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Sep 10, 2019
| // There's a pending update that falls outside the range of | ||
| // suspended work. | ||
| if (firstPendingTime > expirationTime) { | ||
| return renderRoot.bind(null, root, firstPendingTime); |
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As mentioned in #16663. This needs a replacement (and a test).
sebmarkbage
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Sep 10, 2019
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Closed by ab4951f |
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Based on #16663
Given a FiberRoot, we should be able to determine the next expiration time that needs to be worked on, taking into account the levels that are pending, suspended, pinged, and so on.
This removes the
expirationTimeargument fromscheduleCallbackForRoot, and renames it toensureRootIsScheduledto reflect the new signature. The expiration time is instead read from the root using a new function,getNextExpirationTimeToWorkOn.The next step will be to remove the
expirationTimeargument fromrenderRoot, too.