refactor(allocator): remove sentinel empty chunk#21775
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graphite-app[bot] merged 1 commit intomainfrom Apr 26, 2026
Merged
refactor(allocator): remove sentinel empty chunk#21775graphite-app[bot] merged 1 commit intomainfrom
graphite-app[bot] merged 1 commit intomainfrom
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Pull request overview
This PR refactors oxc_allocator::arena::Arena’s chunk linked-list termination from a static sentinel footer to Option<NonNull<ChunkFooter>>, making an empty arena explicitly represented by None and using a dangling aligned pointer for start_ptr/cursor_ptr in the empty state.
Changes:
- Replaces the static empty chunk sentinel with
None-terminated chunk links (current_chunk_footer_ptrandprevious_chunk_footer_ptrbecomeOption). - Introduces
EMPTY_ARENA_DATA_PTRas the empty-arena sentinel forstart_ptr/cursor_ptrand adjusts constructors/iterators/drop/reset accordingly. - Updates raw-parts helpers and tests to work with the new
Option-based representation.
Reviewed changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.
Show a summary per file
| File | Description |
|---|---|
| crates/oxc_allocator/src/arena/tests_alloc.rs | Updates test arena construction to use Some(footer_ptr) for the current chunk. |
| crates/oxc_allocator/src/arena/mod.rs | Changes Arena and ChunkFooter pointer fields to Option, removes the static empty footer, adds EMPTY_ARENA_DATA_PTR. |
| crates/oxc_allocator/src/arena/from_raw_parts.rs | Adjusts raw-parts initialization and pointer accessors for Option footer pointers and empty-arena behavior. |
| crates/oxc_allocator/src/arena/drop.rs | Updates reset/drop chunk traversal and deallocation to stop at None rather than a sentinel footer. |
| crates/oxc_allocator/src/arena/create.rs | Refactors new_impl/new_chunk APIs for the new representation and updates constructors. |
| crates/oxc_allocator/src/arena/chunks.rs | Updates accounting and iterators to traverse until None and changes iterator state to Option. |
| crates/oxc_allocator/src/arena/alloc_impl.rs | Updates slow-path chunk growth and retirement logic to handle empty arenas (None) safely. |
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This was referenced Apr 26, 2026
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The chunks in an `Arena` form a linked list. Previously the list was terminated with a canonical empty chunk, defined as a `static`. Now that we store `start_ptr` and `cursor_ptr` in `Arena` itself (#21483), an empty `Arena` doesn't need to have a pointer to a chunk. Remove the empty chunk, and use `None` to signify the end of the linked list instead. This makes checking "is this chunk the last?" a little cheaper (comparison to 0, not a 64-bit static value), and feels less hacky, and more explicit. It also removes the potential hazard of accidentally mutating the immutable `static` empty chunk.
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April 26, 2026 22:05
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The chunks in an
Arenaform a linked list. Previously the list was terminated with a canonical empty chunk, defined as astatic.Now that we store
start_ptrandcursor_ptrinArenaitself (#21483), an emptyArenadoesn't need to have a pointer to a chunk.Remove the empty chunk, and use
Noneto signify the end of the linked list instead.This makes checking "is this chunk the last?" a little cheaper (comparison to 0, not a 64-bit static value), and feels less hacky, and more explicit. It also removes the potential hazard of accidentally mutating the immutable
staticempty chunk.