https://github.com/python/cpython/commit/7642070807ea45f4e496c01b7a46cfac9cc579b5
commit: 7642070807ea45f4e496c01b7a46cfac9cc579b5
branch: 3.14
author: Hugo van Kemenade <[email protected]>
committer: hugovk <[email protected]>
date: 2025-12-01T20:34:37+02:00
summary:
[3.14] Revert "GH-91636: Clear weakrefs created by finalizers. (GH-136401)
(#141993)" (#142152)
files:
D
Misc/NEWS.d/next/Core_and_Builtins/2025-07-07-17-26-06.gh-issue-91636.GyHU72.rst
M Lib/test/test_gc.py
M Python/gc.c
M Python/gc_free_threading.c
diff --git a/Lib/test/test_gc.py b/Lib/test/test_gc.py
index 7fd339f1ad7184..a6adc2c98514ba 100644
--- a/Lib/test/test_gc.py
+++ b/Lib/test/test_gc.py
@@ -262,11 +262,9 @@ class Cyclic(tuple):
# finalizer.
def __del__(self):
- # 5. Create a weakref to `func` now. In previous
- # versions of Python, this would avoid having it
- # cleared by the garbage collector before calling
- # the finalizers. Now, weakrefs get cleared after
- # calling finalizers.
+ # 5. Create a weakref to `func` now. If we had created
+ # it earlier, it would have been cleared by the
+ # garbage collector before calling the finalizers.
self[1].ref = weakref.ref(self[0])
# 6. Drop the global reference to `latefin`. The only
@@ -295,18 +293,14 @@ def func():
# which will find `cyc` and `func` as garbage.
gc.collect()
- # 9. Previously, this would crash because the weakref
- # created in the finalizer revealed the function after
- # `tp_clear` was called and `func_qualname`
- # had been NULL-ed out by func_clear(). Now, we clear
- # weakrefs to unreachable objects before calling `tp_clear`
- # but after calling finalizers.
+ # 9. Previously, this would crash because `func_qualname`
+ # had been NULL-ed out by func_clear().
print(f"{func=}")
"""
+ # We're mostly just checking that this doesn't crash.
rc, stdout, stderr = assert_python_ok("-c", code)
self.assertEqual(rc, 0)
- # The `func` global is None because the weakref was cleared.
- self.assertRegex(stdout, rb"""\A\s*func=None""")
+ self.assertRegex(stdout, rb"""\A\s*func=<function at \S+>\s*\z""")
self.assertFalse(stderr)
@refcount_test
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2025-07-07-17-26-06.gh-issue-91636.GyHU72.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2025-07-07-17-26-06.gh-issue-91636.GyHU72.rst
deleted file mode 100644
index 09c192f9c5657e..00000000000000
---
a/Misc/NEWS.d/next/Core_and_Builtins/2025-07-07-17-26-06.gh-issue-91636.GyHU72.rst
+++ /dev/null
@@ -1,3 +0,0 @@
-While performing garbage collection, clear weakrefs to unreachable objects
-that are created during running of finalizers. If those weakrefs were are
-not cleared, they could reveal unreachable objects.
diff --git a/Python/gc.c b/Python/gc.c
index c134dc57e28f6d..c87d714ce4cfb1 100644
--- a/Python/gc.c
+++ b/Python/gc.c
@@ -870,7 +870,7 @@ move_legacy_finalizer_reachable(PyGC_Head *finalizers)
* no object in `unreachable` is weakly referenced anymore.
*/
static int
-handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old, bool allow_callbacks)
+handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old)
{
PyGC_Head *gc;
PyObject *op; /* generally FROM_GC(gc) */
@@ -879,9 +879,7 @@ handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old,
bool allow_callbacks)
PyGC_Head *next;
int num_freed = 0;
- if (allow_callbacks) {
- gc_list_init(&wrcb_to_call);
- }
+ gc_list_init(&wrcb_to_call);
/* Clear all weakrefs to the objects in unreachable. If such a weakref
* also has a callback, move it into `wrcb_to_call` if the callback
@@ -937,11 +935,6 @@ handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old,
bool allow_callbacks)
_PyObject_ASSERT((PyObject *)wr, wr->wr_object == op);
_PyWeakref_ClearRef(wr);
_PyObject_ASSERT((PyObject *)wr, wr->wr_object == Py_None);
-
- if (!allow_callbacks) {
- continue;
- }
-
if (wr->wr_callback == NULL) {
/* no callback */
continue;
@@ -994,10 +987,6 @@ handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old,
bool allow_callbacks)
}
}
- if (!allow_callbacks) {
- return 0;
- }
-
/* Invoke the callbacks we decided to honor. It's safe to invoke them
* because they can't reference unreachable objects.
*/
@@ -1750,7 +1739,7 @@ gc_collect_region(PyThreadState *tstate,
}
/* Clear weakrefs and invoke callbacks as necessary. */
- stats->collected += handle_weakrefs(&unreachable, to, true);
+ stats->collected += handle_weakrefs(&unreachable, to);
gc_list_validate_space(to, gcstate->visited_space);
validate_list(to, collecting_clear_unreachable_clear);
validate_list(&unreachable, collecting_set_unreachable_clear);
@@ -1764,14 +1753,6 @@ gc_collect_region(PyThreadState *tstate,
gc_list_init(&final_unreachable);
handle_resurrected_objects(&unreachable, &final_unreachable, to);
- /* Clear weakrefs to objects in the unreachable set. No Python-level
- * code must be allowed to access those unreachable objects. During
- * delete_garbage(), finalizers outside the unreachable set might run
- * and create new weakrefs. If those weakrefs were not cleared, they
- * could reveal unreachable objects. Callbacks are not executed.
- */
- handle_weakrefs(&final_unreachable, NULL, false);
-
/* Call tp_clear on objects in the final_unreachable set. This will cause
* the reference cycles to be broken. It may also cause some objects
* in finalizers to be freed.
diff --git a/Python/gc_free_threading.c b/Python/gc_free_threading.c
index 43add9bc8b7eda..94c77991f5f45b 100644
--- a/Python/gc_free_threading.c
+++ b/Python/gc_free_threading.c
@@ -1493,9 +1493,9 @@ move_legacy_finalizer_reachable(struct collection_state
*state)
}
// Clear all weakrefs to unreachable objects. Weakrefs with callbacks are
-// optionally enqueued in `wrcb_to_call`, but not invoked yet.
+// enqueued in `wrcb_to_call`, but not invoked yet.
static void
-clear_weakrefs(struct collection_state *state, bool enqueue_callbacks)
+clear_weakrefs(struct collection_state *state)
{
PyObject *op;
WORKSTACK_FOR_EACH(&state->unreachable, op) {
@@ -1527,10 +1527,6 @@ clear_weakrefs(struct collection_state *state, bool
enqueue_callbacks)
_PyWeakref_ClearRef(wr);
_PyObject_ASSERT((PyObject *)wr, wr->wr_object == Py_None);
- if (!enqueue_callbacks) {
- continue;
- }
-
// We do not invoke callbacks for weakrefs that are themselves
// unreachable. This is partly for historical reasons: weakrefs
// predate safe object finalization, and a weakref that is itself
@@ -2216,7 +2212,7 @@ gc_collect_internal(PyInterpreterState *interp, struct
collection_state *state,
interp->gc.long_lived_total = state->long_lived_total;
// Clear weakrefs and enqueue callbacks (but do not call them).
- clear_weakrefs(state, true);
+ clear_weakrefs(state);
_PyEval_StartTheWorld(interp);
// Deallocate any object from the refcount merge step
@@ -2227,19 +2223,11 @@ gc_collect_internal(PyInterpreterState *interp, struct
collection_state *state,
call_weakref_callbacks(state);
finalize_garbage(state);
- _PyEval_StopTheWorld(interp);
// Handle any objects that may have resurrected after the finalization.
+ _PyEval_StopTheWorld(interp);
err = handle_resurrected_objects(state);
// Clear free lists in all threads
_PyGC_ClearAllFreeLists(interp);
- if (err == 0) {
- // Clear weakrefs to objects in the unreachable set. No Python-level
- // code must be allowed to access those unreachable objects. During
- // delete_garbage(), finalizers outside the unreachable set might
- // run and create new weakrefs. If those weakrefs were not cleared,
- // they could reveal unreachable objects.
- clear_weakrefs(state, false);
- }
_PyEval_StartTheWorld(interp);
if (err < 0) {
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