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Merged
youknowone merged 1 commit into from
Feb 3, 2026
Merged

Improve object traversal for heap types and mro #6976

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3 changes: 1 addition & 2 deletions crates/vm/src/builtins/type.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -49,8 +49,7 @@ unsafe impl crate::object::Traverse for PyType {
fn traverse(&self, tracer_fn: &mut crate::object::TraverseFn<'_>) {
self.base.traverse(tracer_fn);
self.bases.traverse(tracer_fn);
// mro contains self as mro[0], so skip traversing to avoid circular reference
// self.mro.traverse(tracer_fn);
self.mro.traverse(tracer_fn);
self.subclasses.traverse(tracer_fn);
self.attributes
.read_recursive()
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23 changes: 16 additions & 7 deletions crates/vm/src/object/traverse_object.rs
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Expand Up @@ -45,9 +45,16 @@ unsafe impl Traverse for InstanceDict {
unsafe impl Traverse for PyInner<Erased> {
/// Because PyObject hold a `PyInner<Erased>`, so we need to trace it
fn traverse(&self, tracer_fn: &mut TraverseFn<'_>) {
// 1. trace `dict` and `slots` field(`typ` can't trace for it's a AtomicRef while is leaked by design)
// 2. call vtable's trace function to trace payload
// self.typ.trace(tracer_fn);
// For heap type instances, traverse the type reference.
// PyAtomicRef holds a strong reference (via PyRef::leak), so GC must
// account for it to correctly detect instance ↔ type cycles.
// Static types are always alive and don't need this.
let typ = &*self.typ;
if typ.heaptype_ext.is_some() {
// Safety: Py<PyType> and PyObject share the same memory layout
let typ_obj: &PyObject = unsafe { &*(typ as *const _ as *const PyObject) };
tracer_fn(typ_obj);
}
self.dict.traverse(tracer_fn);
// weak_list is inline atomic pointers, no heap allocation, no trace
self.slots.traverse(tracer_fn);
Expand All @@ -64,10 +71,12 @@ unsafe impl Traverse for PyInner<Erased> {
unsafe impl<T: MaybeTraverse> Traverse for PyInner<T> {
/// Type is known, so we can call `try_trace` directly instead of using erased type vtable
fn traverse(&self, tracer_fn: &mut TraverseFn<'_>) {
// 1. trace `dict` and `slots` field(`typ` can't trace for it's a AtomicRef while is leaked by design)
// 2. call corresponding `try_trace` function to trace payload
// (No need to call vtable's trace function because we already know the type)
// self.typ.trace(tracer_fn);
// For heap type instances, traverse the type reference (same as erased version)
let typ = &*self.typ;
if typ.heaptype_ext.is_some() {
let typ_obj: &PyObject = unsafe { &*(typ as *const _ as *const PyObject) };
tracer_fn(typ_obj);
}
self.dict.traverse(tracer_fn);
// weak_list is inline atomic pointers, no heap allocation, no trace
self.slots.traverse(tracer_fn);
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