cherry-pick(4.4-stable): Android ANR deadlock between CSS updates-registry lock and Fabric commit (#9715)#9736
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…c commit (#9715) ## Issue On Android, screens using a relative CSS length (e.g. a `transformOrigin` mixing `%` and `px`) could freeze (ANR). Resolving the relative length read the live ShadowTree, which takes the ShadowTree commit lock, while holding Reanimated's updates-registry lock; a concurrent Fabric commit takes the same two locks in the opposite order, so they deadlock (AB-BA). Regression from #9495. ## Fix Resolve relative lengths against the last mounted tree instead of the live ShadowTree, so the read path never takes the ShadowTree lock. `ReanimatedMountHook` records the mounted root per surface (under the registry lock it already holds), and `ViewStylesRepository` reads layout from that snapshot via a plain parent/child walk. With lock A gone from Reanimated's read path, the AB-BA cycle can't form. Animation-backend mode keeps reading the live tree (its commit hook is disabled there, so there is no deadlock to avoid). Verified on device: Android (deadlock gone) and iOS (relative resolution correct).
tjzel
approved these changes
Jun 23, 2026
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Summary
Cherry-picking for Reanimated 4.4.2 release