1#ifndef Py_CPYTHON_WEAKREFOBJECT_H
2# error "this header file must not be included directly"
3#endif
4
5/* PyWeakReference is the base struct for the Python ReferenceType, ProxyType,
6 * and CallableProxyType.
7 */
8struct _PyWeakReference {
9 PyObject_HEAD
10
11 /* The object to which this is a weak reference, or Py_None if none.
12 * Note that this is a stealth reference: wr_object's refcount is
13 * not incremented to reflect this pointer.
14 */
15 PyObject *wr_object;
16
17 /* A callable to invoke when wr_object dies, or NULL if none. */
18 PyObject *wr_callback;
19
20 /* A cache for wr_object's hash code. As usual for hashes, this is -1
21 * if the hash code isn't known yet.
22 */
23 Py_hash_t hash;
24
25 /* If wr_object is weakly referenced, wr_object has a doubly-linked NULL-
26 * terminated list of weak references to it. These are the list pointers.
27 * If wr_object goes away, wr_object is set to Py_None, and these pointers
28 * have no meaning then.
29 */
30 PyWeakReference *wr_prev;
31 PyWeakReference *wr_next;
32 vectorcallfunc vectorcall;
33};
34
35PyAPI_FUNC(Py_ssize_t) _PyWeakref_GetWeakrefCount(PyWeakReference *head);
36
37PyAPI_FUNC(void) _PyWeakref_ClearRef(PyWeakReference *self);
38
39static inline PyObject* PyWeakref_GET_OBJECT(PyObject *ref_obj) {
40 PyWeakReference *ref;
41 PyObject *obj;
42 assert(PyWeakref_Check(ref_obj));
43 ref = _Py_CAST(PyWeakReference*, ref_obj);
44 obj = ref->wr_object;
45 // Explanation for the Py_REFCNT() check: when a weakref's target is part
46 // of a long chain of deallocations which triggers the trashcan mechanism,
47 // clearing the weakrefs can be delayed long after the target's refcount
48 // has dropped to zero. In the meantime, code accessing the weakref will
49 // be able to "see" the target object even though it is supposed to be
50 // unreachable. See issue gh-60806.
51 if (Py_REFCNT(obj) > 0) {
52 return obj;
53 }
54 return Py_None;
55}
56#define PyWeakref_GET_OBJECT(ref) PyWeakref_GET_OBJECT(_PyObject_CAST(ref))
57

source code of include/python3.12/cpython/weakrefobject.h