bpo-40504: Allow weakrefs to lru_cache objects

Lib/test/test_functools.py

@@ -14,6 +14,8 @@
 import unittest
 import unittest.mock
 import os
+import weakref
+import gc
 from weakref import proxy
 import contextlib
 
@@ -1938,6 +1940,35 @@ def f():
  return 1
  self.assertEqual(f.cache_parameters(), {'maxsize': 1000, "typed": True})
 
+ def test_lru_cache_weakrefable(self):
+ @self.module.lru_cache
+ def test_function(x):
+ return x
+
+ class A:
+ @self.module.lru_cache
+ def test_method(self, x):
+ return (self, x)
+
+ @staticmethod
+ @self.module.lru_cache
+ def test_staticmethod(x):
+ return (self, x)
+
+ refs = [weakref.ref(test_function),
+ weakref.ref(A.test_method),
+ weakref.ref(A.test_staticmethod)]
+
+ for ref in refs:
+ self.assertIsNotNone(ref())
+
+ del A
+ del test_function
+ gc.collect()
+
+ for ref in refs:
+ self.assertIsNone(ref())
+
 
 @py_functools.lru_cache()
 def py_cached_func(x, y):

Misc/NEWS.d/next/Library/2020-05-05-17-12-47.bpo-40504.EX6wPn.rst

@@ -0,0 +1 @@
+:func:`functools.lru_cache` objects can now be the targets of weakrefs.

Modules/_functoolsmodule.c

@@ -783,6 +783,7 @@ typedef struct lru_cache_object {
  Py_ssize_t misses;
  PyObject *cache_info_type;
  PyObject *dict;
+ PyObject *weakreflist;
 } lru_cache_object;
 
 static PyTypeObject lru_cache_type;
@@ -1196,6 +1197,7 @@ lru_cache_new(PyTypeObject *type, PyObject *args, PyObject *kw)
  Py_INCREF(cache_info_type);
  obj->cache_info_type = cache_info_type;
  obj->dict = NULL;
+ obj->weakreflist = NULL;
  return (PyObject *)obj;
 }
 
@@ -1227,6 +1229,8 @@ lru_cache_dealloc(lru_cache_object *obj)
  lru_list_elem *list;
  /* bpo-31095: UnTrack is needed before calling any callbacks */
  PyObject_GC_UnTrack(obj);
+ if (obj->weakreflist != NULL)
+ PyObject_ClearWeakRefs((PyObject*)obj);
 
  list = lru_cache_unlink_list(obj);
  Py_XDECREF(obj->cache);
@@ -1384,7 +1388,8 @@ static PyTypeObject lru_cache_type = {
  (traverseproc)lru_cache_tp_traverse,/* tp_traverse */
  (inquiry)lru_cache_tp_clear, /* tp_clear */
  0, /* tp_richcompare */
- 0, /* tp_weaklistoffset */
+ offsetof(lru_cache_object, weakreflist),
+ /* tp_weaklistoffset */
  0, /* tp_iter */
  0, /* tp_iternext */
  lru_cache_methods, /* tp_methods */