https://github.com/python/cpython/commit/795d5c5b44c5ac4b7d1619800f341ec2d0332430
commit: 795d5c5b44c5ac4b7d1619800f341ec2d0332430
branch: main
author: Neil Schemenauer <[email protected]>
committer: encukou <[email protected]>
date: 2026-01-20T14:45:12+01:00
summary:
gh-144054: shutdown fix for deferred ref counting (GH-144055)
When shutting down, disable deferred refcounting for all GC objects. It
is important to do this also for untracked objects, which before this
change were getting missed.
Small code cleanup:
We can remove the shutdown case disable_deferred_refcounting() call
inside scan_heap_visitor() if we are careful about it. The key is
that frame_disable_deferred_refcounting() might fail if the object
is untracked.
files:
M Python/gc_free_threading.c
diff --git a/Python/gc_free_threading.c b/Python/gc_free_threading.c
index 51261cea0cfe2c..beb3fa588f40e7 100644
--- a/Python/gc_free_threading.c
+++ b/Python/gc_free_threading.c
@@ -308,17 +308,18 @@ disable_deferred_refcounting(PyObject *op)
// should also be disabled when we turn off deferred refcounting.
_PyObject_DisablePerThreadRefcounting(op);
}
-
- // Generators and frame objects may contain deferred references to other
- // objects. If the pointed-to objects are part of cyclic trash, we may
- // have disabled deferred refcounting on them and need to ensure that we
- // use strong references, in case the generator or frame object is
- // resurrected by a finalizer.
- if (PyGen_CheckExact(op) || PyCoro_CheckExact(op) ||
PyAsyncGen_CheckExact(op)) {
- frame_disable_deferred_refcounting(&((PyGenObject *)op)->gi_iframe);
- }
- else if (PyFrame_Check(op)) {
- frame_disable_deferred_refcounting(((PyFrameObject *)op)->f_frame);
+ if (_PyObject_GC_IS_TRACKED(op)) {
+ // Generators and frame objects may contain deferred references to
other
+ // objects. If the pointed-to objects are part of cyclic trash, we may
+ // have disabled deferred refcounting on them and need to ensure that
we
+ // use strong references, in case the generator or frame object is
+ // resurrected by a finalizer.
+ if (PyGen_CheckExact(op) || PyCoro_CheckExact(op) ||
PyAsyncGen_CheckExact(op)) {
+ frame_disable_deferred_refcounting(&((PyGenObject
*)op)->gi_iframe);
+ }
+ else if (PyFrame_Check(op)) {
+ frame_disable_deferred_refcounting(((PyFrameObject *)op)->f_frame);
+ }
}
}
@@ -1240,19 +1241,30 @@ scan_heap_visitor(const mi_heap_t *heap, const
mi_heap_area_t *area,
return true;
}
- if (state->reason == _Py_GC_REASON_SHUTDOWN) {
- // Disable deferred refcounting for reachable objects as well during
- // interpreter shutdown. This ensures that these objects are collected
- // immediately when their last reference is removed.
- disable_deferred_refcounting(op);
- }
-
// object is reachable, restore `ob_tid`; we're done with these objects
gc_restore_tid(op);
gc_clear_alive(op);
return true;
}
+// Disable deferred refcounting for reachable objects during interpreter
+// shutdown. This ensures that these objects are collected immediately when
+// their last reference is removed. This needs to consider both tracked and
+// untracked GC objects, since either might have deferred refcounts enabled.
+static bool
+scan_heap_disable_deferred(const mi_heap_t *heap, const mi_heap_area_t *area,
+ void *block, size_t block_size, void *args)
+{
+ PyObject *op = op_from_block_all_gc(block, args);
+ if (op == NULL) {
+ return true;
+ }
+ if (!_Py_IsImmortal(op)) {
+ disable_deferred_refcounting(op);
+ }
+ return true;
+}
+
static int
move_legacy_finalizer_reachable(struct collection_state *state);
@@ -1487,6 +1499,10 @@ deduce_unreachable_heap(PyInterpreterState *interp,
// Restores ob_tid for reachable objects.
gc_visit_heaps(interp, &scan_heap_visitor, &state->base);
+ if (state->reason == _Py_GC_REASON_SHUTDOWN) {
+ gc_visit_heaps(interp, &scan_heap_disable_deferred, &state->base);
+ }
+
if (state->legacy_finalizers.head) {
// There may be objects reachable from legacy finalizers that are in
// the unreachable set. We need to mark them as reachable.
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