Issue #16602: When a weakref's target was part of a long deallocation chain, the object could remain reachable through its weakref even though its refcount had dropped to zero.
Thanks to Eugene Toder for diagnosing and reporting the issue.
diff --git a/Lib/test/test_weakref.py b/Lib/test/test_weakref.py
index b7c72bd..3d86cb7 100644
--- a/Lib/test/test_weakref.py
+++ b/Lib/test/test_weakref.py
@@ -774,6 +774,27 @@
self.assertEqual(hash(a), hash(42))
self.assertRaises(TypeError, hash, b)
+ def test_trashcan_16602(self):
+ # Issue #16602: when a weakref's target was part of a long
+ # deallocation chain, the trashcan mechanism could delay clearing
+ # of the weakref and make the target object visible from outside
+ # code even though its refcount had dropped to 0. A crash ensued.
+ class C(object):
+ def __init__(self, parent):
+ if not parent:
+ return
+ wself = weakref.ref(self)
+ def cb(wparent):
+ o = wself()
+ self.wparent = weakref.ref(parent, cb)
+
+ d = weakref.WeakKeyDictionary()
+ root = c = C(None)
+ for n in range(100):
+ d[c] = c = C(c)
+ del root
+ gc.collect()
+
class SubclassableWeakrefTestCase(TestBase):