Add eager alternate.stateNode cleanup #33161
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Comparing: 21fdf30...a721b37 Critical size changesIncludes critical production bundles, as well as any change greater than 2%:
Significant size changesIncludes any change greater than 0.2%: (No significant changes) |
sebmarkbage
reviewed
May 9, 2025
| @@ -2171,6 +2172,11 @@ function commitMutationEffectsOnFiber( | |||
| } | |||
| } | |||
| } | |||
| if (enableEagerAlternateStateNodeCleanup) { | |||
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This should be in the else branch of if (supportsMutation) and it should check if (supportsPersistence) since this should only apply to the persistent mode which is the only mode that clones the state nodes.
The flag is only on in RN but it's still on for Paper unnecessarily. You're better off turning the flag on everywhere else because that flushes out any issues where it would have issues if it turned on in the other renders. Like not gating it properly on supportsPersistence.
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This is a fix for a problem where React retains shadow nodes longer than it needs to. The behaviour is shown in React Native test: https://github.com/facebook/react-native/blob/main/packages/react-native/src/private/__tests__/utilities/__tests__/ShadowNodeReferenceCounter-itest.js#L169
Problem
When React commits a new shadow tree, old shadow nodes are stored inside
fiber.alternate.stateNode. This is not cleared up until React clones the node again. This may be problematic if mutation deletes a subtree, in that casefiber.alternate.stateNodewill retain entire subtree until next update. In case of image nodes, this means retaining entire images.So when React goes from revision A:
<View><View /></View>to revision B:<View />,fiber.alternate.stateNodewill be pointing to Shadow Node that represents revision A..Fix
To fix this, this PR adds a new feature flag
enableEagerAlternateStateNodeCleanup. When enabled,alternate.stateNodeis proactively pointed towards finishedWork's stateNode, releasing resources sooner.I have verified this fixes the issue demonstrated by React Native tests.
All existing React tests pass when the flag is enabled.