Issue 3110: Crash with weakref subclass,

seen after a "import multiprocessing.reduction"

An instance of a weakref subclass can have attributes.
If such a weakref holds the only strong reference to the object,
deleting the weakref will delete the object. In this case,
the callback must not be called, because the ref object is being deleted!

Backport of r34309
This commit is contained in:
Amaury Forgeot d'Arc 2008-06-16 19:22:42 +00:00
parent 75ee9eb9c6
commit 3255e134fe
3 changed files with 55 additions and 5 deletions

View File

@ -645,7 +645,7 @@ class ReferencesTestCase(TestBase):
w = Target()
class SubclassableWeakrefTestCase(unittest.TestCase):
class SubclassableWeakrefTestCase(TestBase):
def test_subclass_refs(self):
class MyRef(weakref.ref):
@ -709,6 +709,44 @@ class SubclassableWeakrefTestCase(unittest.TestCase):
self.assertEqual(r.meth(), "abcdef")
self.failIf(hasattr(r, "__dict__"))
def test_subclass_refs_with_cycle(self):
# Bug #3110
# An instance of a weakref subclass can have attributes.
# If such a weakref holds the only strong reference to the object,
# deleting the weakref will delete the object. In this case,
# the callback must not be called, because the ref object is
# being deleted.
class MyRef(weakref.ref):
pass
# Use a local callback, for "regrtest -R::"
# to detect refcounting problems
def callback(w):
self.cbcalled += 1
o = C()
r1 = MyRef(o, callback)
r1.o = o
del o
del r1 # Used to crash here
self.assertEqual(self.cbcalled, 0)
# Same test, with two weakrefs to the same object
# (since code paths are different)
o = C()
r1 = MyRef(o, callback)
r2 = MyRef(o, callback)
r1.r = r2
r2.o = o
del o
del r2
del r1 # Used to crash here
self.assertEqual(self.cbcalled, 0)
class Object:
def __init__(self, arg):
@ -1150,6 +1188,7 @@ def test_main():
MappingTestCase,
WeakValueDictionaryTestCase,
WeakKeyDictionaryTestCase,
SubclassableWeakrefTestCase,
)
test_support.run_doctest(sys.modules[__name__])

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@ -12,6 +12,9 @@ What's New in Python 2.5.3?
Core and builtins
-----------------
- Issue #3100: Corrected a crash on deallocation of a subclassed weakref which
holds the last (strong) reference to its referent.
- Issue #1686386: Tuple's tp_repr did not take into account the possibility of
having a self-referential tuple, which is possible from C code. Nor did
object's tp_str consider that a type's tp_str could do something that could

View File

@ -900,7 +900,8 @@ PyObject_ClearWeakRefs(PyObject *object)
current->wr_callback = NULL;
clear_weakref(current);
if (callback != NULL) {
handle_callback(current, callback);
if (current->ob_refcnt > 0)
handle_callback(current, callback);
Py_DECREF(callback);
}
}
@ -918,9 +919,15 @@ PyObject_ClearWeakRefs(PyObject *object)
for (i = 0; i < count; ++i) {
PyWeakReference *next = current->wr_next;
Py_INCREF(current);
PyTuple_SET_ITEM(tuple, i * 2, (PyObject *) current);
PyTuple_SET_ITEM(tuple, i * 2 + 1, current->wr_callback);
if (current->ob_refcnt > 0)
{
Py_INCREF(current);
PyTuple_SET_ITEM(tuple, i * 2, (PyObject *) current);
PyTuple_SET_ITEM(tuple, i * 2 + 1, current->wr_callback);
}
else {
Py_DECREF(current->wr_callback);
}
current->wr_callback = NULL;
clear_weakref(current);
current = next;
@ -928,6 +935,7 @@ PyObject_ClearWeakRefs(PyObject *object)
for (i = 0; i < count; ++i) {
PyObject *callback = PyTuple_GET_ITEM(tuple, i * 2 + 1);
/* The tuple may have slots left to NULL */
if (callback != NULL) {
PyObject *item = PyTuple_GET_ITEM(tuple, i * 2);
handle_callback((PyWeakReference *)item, callback);