refactor(allocator): improve safety of dealloc_chunk_list#21779
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graphite-app[bot] merged 1 commit intomainfrom Apr 26, 2026
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Merging this PR will not alter performance
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Pull request overview
This PR refactors Arena’s chunk deallocation helper to make aliasing/lifetime boundaries around ChunkFooter references explicit, reduce the scope of unsafe blocks, and document the safety assumptions involved in freeing arena chunks.
Changes:
- Refactors
dealloc_chunk_listto ensure&ChunkFooterborrows are not live acrossdealloc. - Narrows
unsafeblocks to only the operations that require them. - Adds safety documentation/comments explaining required invariants.
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Improve the safety of `Arena`'s `dealloc_chunk_list` function:
- Ensure `&ChunkFooter` reference is not live when the chunk containing that `ChunkFooter` is deallocated.
- Scope `unsafe { ... }` blocks to cover just the statements that require them.
- Document the safety invariants.
I don't believe there was a soundness issue here (as `&ChunkFooter` references were short-lived), but this change makes the importance of avoiding live references clear, and explicitly guards against it.
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April 26, 2026 22:09
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Improve the safety of
Arena'sdealloc_chunk_listfunction:&ChunkFooterreference is not live when the chunk containing thatChunkFooteris deallocated.unsafe { ... }blocks to cover just the statements that require them.I don't believe there was a soundness issue here (as
&ChunkFooterreferences were short-lived), but this change makes the importance of avoiding live references clear, and explicitly guards against it.