[react-refresh] fix memory leak: only add root to helpersByRoot on mount#36382
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sleitor wants to merge 1 commit intofacebook:mainfrom
Open
[react-refresh] fix memory leak: only add root to helpersByRoot on mount#36382sleitor wants to merge 1 commit intofacebook:mainfrom
sleitor wants to merge 1 commit intofacebook:mainfrom
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helpersByRoot.set(root, helpers) was called unconditionally on every onCommitFiberRoot invocation, including re-renders after unmount. This caused secondary renderer roots (e.g. react-three-fiber Canvas) to remain in the helpersByRoot Map permanently, preventing GC. Fix: - Move helpersByRoot.set(root, helpers) into the mount branches only (!wasMounted && isMounted, and the no-alternate initial mount path). - Skip helpersByRoot.set for the update case (wasMounted && isMounted) since the root is already in the Map from the initial mount. - Guard failedRoots.add in the (!wasMounted && !isMounted && didError) case with helpersByRoot.has(root) to avoid retaining roots that were never successfully mounted. Fixes facebook#36379
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Summary
Fixes #36379
Problem
helpersByRoot.set(root, helpers)was called unconditionally on everyonCommitFiberRootinvocation. This means that even after a root is unmounted (and correctly deleted fromhelpersByRootin thewasMounted && !isMountedbranch), any subsequent commit from that renderer ID would re-add the root to the Map.This causes memory leaks for secondary renderers such as react-three-fiber, where Canvas roots are repeatedly mounted and unmounted. The
helpersByRootMap grows without bound, preventing garbage collection of fiber roots and their associated component trees.Fix
Move
helpersByRoot.set(root, helpers)into the mount branches only:!wasMounted && isMounted(new mount with an existing alternate): set the root inhelpersByRoot.else(first mount without alternate): set the root inhelpersByRoot.wasMounted && isMounted(update): no change needed — root is already in the Map from the initial mount.!wasMounted && !isMounted && didError: guardfailedRoots.add(root)withhelpersByRoot.has(root)to avoid retaining roots that were never successfully mounted.Testing
ReactFreshMultipleRenderer-test.internal.jsexercise the multi-renderer path and should continue to pass.