[FFI] Make Object::unique() require no weak references - #731
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tlopex
approved these changes
Sep 2, 2026
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Summary
Object::unique()require one strong reference and no external weak references by comparing the packed count withkCombinedRefCountBothOne.ObjectPtr<T>::unique()to the object-level implementation while leaving strong-onlyuse_count()semantics unchanged.WeakObjectPtris live.Rationale
unique()gates copy-on-write and in-place mutation. A live weak pointer can still upgrade while the object has a strong owner, so strong-only uniqueness is insufficient for safely choosing in-place mutation. Comparing the combined counter also observes both halves in one atomic load.Compatibility
Out-of-tree users that retain weak references may now copy instead of mutating in place. Current production call sites without weak references retain their existing behavior.