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[web] Defer disposal of stale cached paths to FrameArena - #192072
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This pull request defers the disposal of invalidated backend paths in EnginePath by collecting them in a list and disposing them during the collect phase, preventing premature deallocation during concurrent rasterization. A new test is added to verify concurrent path mutation and rasterization. The review feedback suggests optimizing memory overhead by lazily initializing the stale paths list only when a path is invalidated, and updating the collection logic accordingly.
When mutating an EnginePath after building and drawing it in the same frame, _invalidateCachedPath() was prematurely disposing _cachedPath. In multi-threaded WebAssembly (skwasm), this eager mid-frame deallocation interleaved with background raster thread deallocations, leading to heap corruption and RuntimeError: memory access out of bounds in $emscripten_builtin_free. This change keeps invalidated BackendPath instances alive in _stalePaths until the end of the frame, respecting the FrameArena lifecycle contract. Fixes flutter#191976
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When mutating an
EnginePathafter building and drawing it in the same frame,_invalidateCachedPath()was prematurely disposing_cachedPath.In multi-threaded WebAssembly (
skwasm), this eager mid-frame deallocation violated the lifecycle contract ofFrameArenaand caused native allocations to be freed on the main thread while background raster thread operations were deallocating previous display lists in the same linear memory space, leading to heap corruption andRuntimeError: memory access out of boundsin$emscripten_builtin_free.This change keeps invalidated
BackendPathinstances in_stalePathsuntil the end of the frame whenFrameArena.collect()runs.Fixes #191976
Pre-launch Checklist
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