Serhiy Storchaka added the comment:
Using Py_CLEAR() fixes symptoms in this test, but the real issue is that
deallocating code is executed twice for some objects (for every 25th
OrderedDict).
PyDict_Type.tp_dealloc() can deposit an object in the _PyTrash_delete_later
list if trash_delete_nesting exceeds PyTrash_UNWIND_LEVEL. Later Py_TYPE(op)-
>tp_dealloc is called for objects in the _PyTrash_delete_later list. But this
is odict_dealloc that already was called.
One of ways to avoid repeated deallocation is to change the type of the object
before calling PyDict_Type.tp_dealloc(). This looks as a hack, but correct
hack. May be there is more straightforward solution.
----------
Added file: http://bugs.python.org/file40808/odict-trashcan.v3.patch
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue25395>
_______________________________________
diff -r 741ef17e9b86 Lib/test/test_collections.py
--- a/Lib/test/test_collections.py Sun Oct 18 09:54:42 2015 +0300
+++ b/Lib/test/test_collections.py Sun Oct 18 13:28:41 2015 +0300
@@ -2033,6 +2033,14 @@ class OrderedDictTests:
items = [('a', 1), ('c', 3), ('b', 2)]
self.assertEqual(list(MyOD(items).items()), items)
+ def test_highly_nested(self):
+ # Issue 25395: crashes during garbage collection
+ obj = None
+ for _ in range(1000):
+ obj = self.module.OrderedDict([(None, obj)])
+ del obj
+ support.gc_collect()
+
class PurePythonOrderedDictTests(OrderedDictTests, unittest.TestCase):
diff -r 741ef17e9b86 Misc/NEWS
--- a/Misc/NEWS Sun Oct 18 09:54:42 2015 +0300
+++ b/Misc/NEWS Sun Oct 18 13:28:41 2015 +0300
@@ -10,6 +10,9 @@ Release date: XXXX-XX-XX
Core and Builtins
-----------------
+- Issue #25395: Fix crash when highly nested OrderedDict structures were
+ garbage collected.
+
- Issue #25401: Optimize bytes.fromhex() and bytearray.fromhex(): they are now
between 2x and 3.5x faster.
diff -r 741ef17e9b86 Objects/odictobject.c
--- a/Objects/odictobject.c Sun Oct 18 09:54:42 2015 +0300
+++ b/Objects/odictobject.c Sun Oct 18 13:28:41 2015 +0300
@@ -1438,16 +1438,19 @@ static void
odict_dealloc(PyODictObject *self)
{
PyObject_GC_UnTrack(self);
- Py_TRASHCAN_SAFE_BEGIN(self);
+ Py_TRASHCAN_SAFE_BEGIN(self)
+
Py_XDECREF(self->od_inst_dict);
if (self->od_weakreflist != NULL)
PyObject_ClearWeakRefs((PyObject *)self);
_odict_clear_nodes(self);
- Py_TRASHCAN_SAFE_END(self);
/* must be last */
+ Py_TYPE(self) = &PyDict_Type;
PyDict_Type.tp_dealloc((PyObject *)self);
+
+ Py_TRASHCAN_SAFE_END(self)
};
/* tp_repr */
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