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Replace GC tracking HashSet with intrusive linked list #7328

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Merged
youknowone merged 5 commits into from
Mar 4, 2026
+315 −298
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Replace GC tracking HashSet with intrusive linked list #7328

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ff3b939
Replace GC tracking HashSet with intrusive linked list
youknowone Mar 3, 2026
6a40f0f
Auto-format: cargo fmt --all
github-actions[bot] Mar 3, 2026
b279716
Fix race condition: create unreachable_refs under read locks
youknowone Mar 4, 2026
b6d5366
Apply code review feedback from PR #7328
youknowone Mar 4, 2026
2c98e8b
Apply suggestions from code review
youknowone Mar 4, 2026
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Replace GC tracking HashSet with intrusive linked list 
Replace per-generation HashSet<GcObjectPtr> with intrusive doubly-linked
lists for GC object tracking. Each PyInner now carries gc_pointers
(prev/next) and gc_generation fields, enabling O(1) track/untrack
without hashing.

- Add gc_pointers (Pointers<PyObject>) and gc_generation (u8) to PyInner
- Implement GcLink trait for intrusive list integration
- Replace generation_objects/permanent_objects/tracked_objects/finalized_objects
  HashSets with generation_lists/permanent_list LinkedLists
- Use GcBits::FINALIZED flag instead of finalized_objects HashSet
- Change default_dealloc to untrack directly before memory free
- Hold both src/dst list locks in promote_survivors to prevent race
  conditions with concurrent untrack_object calls
- Add pop_front to LinkedList for freeze/unfreeze operations
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@youknowone
youknowone committed Mar 4, 2026
commit ff3b939186563d5dcd0a6a609e331468ec2d58eb
14 changes: 14 additions & 0 deletions crates/common/src/linked_list.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -192,6 +192,20 @@ impl<L: Link> LinkedList<L, L::Target> {
// }
// }

/// Removes the first element from the list and returns it, or None if empty.
pub fn pop_front(&mut self) -> Option<L::Handle> {
let head = self.head?;
unsafe {
self.head = L::pointers(head).as_ref().get_next();
if let Some(new_head) = self.head {
L::pointers(new_head).as_mut().set_prev(None);
}
L::pointers(head).as_mut().set_next(None);
L::pointers(head).as_mut().set_prev(None);
Some(L::from_raw(head))
}
}

/// Returns whether the linked list does not contain any node
pub const fn is_empty(&self) -> bool {
self.head.is_none()
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