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#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
57#  define PyWeakref_GET_OBJECT(ref) PyWeakref_GET_OBJECT(_PyObject_CAST(ref))
58#endif
59