Idle updates should not be blocked by hidden work #16871
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Use the special `Idle` expiration time for updates that are triggered at Scheduler's `IdlePriority`, instead of `Never`. The key difference between Idle and Never¹ is that Never work can be committed in an inconsistent state without tearing the UI. The main example is offscreen content, like a hidden subtree. ¹ "Never" isn't the best name. I originally called it that because it "never" expires, but neither does Idle. Since it's mostly used for offscreen subtrees, we could call it "Offscreen." However, it's also used for dehydrated Suspense boundaries, which are inconsistent in the sense that they haven't finished yet, but aren't visibly inconsistent because the server rendered HTML matches what the hydrated tree would look like.
Details of bundled changes.Comparing: c5e7190...7ee2a58 react-art
react-dom
react-test-renderer
react-reconciler
react-native-renderer
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I had made them Never to avoid an extra render when a hidden effect updates the hidden component -- if they are Idle, we have to render once at Idle, which bails out on the hidden subtree, then again at Never to actually process the update -- but the problem of needing an extra render pass to bail out hidden updates already exists and we should fix that properly instead of adding yet another special case.
sebmarkbage
approved these changes
Sep 24, 2019
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Use the special
Idleexpiration time for updates that are triggered at Scheduler'sIdlePriority, instead ofNever.The key difference between Idle and Never¹ is that Never work can be committed in an inconsistent state without tearing the UI. The main example is offscreen content, like a hidden subtree.
¹ "Never" isn't the best name. I originally called it that because it "never" expires, but neither does Idle. Since it's mostly used for offscreen subtrees, we could call it "Offscreen." However, it's also used for dehydrated Suspense boundaries, which are inconsistent in the sense that they haven't finished yet, but aren't visibly inconsistent because the server rendered HTML matches what the hydrated tree would look like.