Fix memory leak in AnimatedProps constructor #2809
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Removes __attach() call from AnimatedProps constructor that caused duplicate child additions when combined with lifecycle hook. The constructor was calling __attach(), then useLayoutEffect in useAnimatedProps called it again on the same instance, causing each AnimatedProps to be added as a child twice to its parent nodes. This led to unbounded memory growth in applications with frequent re-renders. This change aligns with React Native core implementation, which does not call __attach() in the AnimatedProps constructor
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Fixes a memory leak in
AnimatedPropsthat causes unbounded accumulation of child nodes in applications with frequent re-renders.Fixes #2756. Builds on recent improvements in this area like #2800.
Background
During investigation of facebook/react-native#49217, I discovered this issue is specific to react-native-web. This area of the vendored Animated implementation has diverged from React Native core, where the
AnimatedPropsconstructor does not call__attach().Root Cause
The
AnimatedPropsconstructor callsthis.__attach()(line 35), thenuseAnimatedPropsLifecyclecallsnode.__attach()again (line 110 inuseAnimatedProps.js). This causes the sameAnimatedPropsinstance to add itself as a child to parent nodes twice.Each re-render creates a new
AnimatedPropswith this double-attachment, but cleanup only removes one reference. The result is unbounded accumulation of duplicate children. In a stress test with 500 animated components re-rendering every 50ms, this produced 359,382 duplicate__addChildcalls.Live demo of the issue (note: Android/iOs works fine, but web version exhibits the leak)
Approach
This PR removes the constructor
__attach()call entirely.Why this is safe:
useLayoutEffectinuseAnimatedProps(line 110) synchronously callsnode.__attach()before browser paintInitially considered adding a defensive check in
__addChild()to prevent duplicates:While this prevented the leak, it masked the underlying issue rather than addressing the root cause.
Impact