Add is_subclass to PyWeakReference and do not clear those weakrefs in GC

python · sergey-miryanov · Jun 19, 2025 · Jun 22, 2025 · Jun 22, 2025 · Jun 22, 2025
commit 3294f2e4cec9c4705fdd338a8b49b6e1a6c84e9f
diff --git a/Include/cpython/weakrefobject.h b/Include/cpython/weakrefobject.h
@@ -38,6 +38,7 @@ struct _PyWeakReference {
      */
     PyMutex *weakrefs_lock;
 #endif
+    uint8_t is_subclass;
 };
 
 PyAPI_FUNC(void) _PyWeakref_ClearRef(PyWeakReference *self);

@@ -9265,6 +9265,9 @@ add_subclass(PyTypeObject *base, PyTypeObject *type)
         return -1;
     }
 
+    ((PyWeakReference*)ref)->is_subclass = 1;
+
+
     // Only get tp_subclasses after creating the key and value.
     // PyWeakref_NewRef() can trigger a garbage collec
8000
tion which can execute
     // arbitrary Python code and so modify base->tp_subclasses.

@@ -72,6 +72,7 @@ init_weakref(PyWeakReference *self, PyObject *ob, PyObject *callback)
     _PyObject_SetMaybeWeakref(ob);
     _PyObject_SetMaybeWeakref((PyObject *)self);
 #endif
+    self->is_subclass = 0;
 }
 
 // Clear the weakref and steal its callback into `callback`, if provided.
-Original file line number
+Diff line change
@@ Expand Up / @@ -38,6 +38,7 @@ struct _PyWeakReference { @@
          */
         PyMutex *weakrefs_lock;
     #endif
+        uint8_t is_subclass;
     };
     PyAPI_FUNC(void) _PyWeakref_ClearRef(PyWeakReference *self);
@@ Expand Down @@