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bpo-40608: restore protection against double-deallocate issue for subclasses of classes that use trashcan #20104

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bpo-40608: restore protection against double-deallocate issue for subclasses of classes that use trashcan #20104

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10 changes: 10 additions & 0 deletions Lib/test/test_capi.py
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Original file line number Diff line number Diff line change
Expand Up @@ -395,6 +395,16 @@ def __del__(self):
del L
self.assertEqual(PyList.num, 0)

def test_subclass_of_base_that_uses_old_macros(self):
class Daisy(_testcapi.OldTrashcanMacros):
pass

DEPTH=150
daisyChain = Daisy()
for x in range(DEPTH):
daisyChain = (Daisy(), daisyChain, Daisy())
daisyChain = None

def test_subclass_of_heap_gc_ctype_with_tpdealloc_decrefs_once(self):
class HeapGcCTypeSubclass(_testcapi.HeapGcCType):
def __init__(self):
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66 changes: 66 additions & 0 deletions Modules/_testcapimodule.c
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Expand Up @@ -6011,6 +6011,67 @@ static PyTypeObject MyList_Type = {
MyList_new, /* tp_new */
};

/* create baseclass using the old trashcan macros (Py_TRASHCAN_SAFE_BEGIN/END) to test backwards compatibility */

typedef struct {
PyObject_HEAD
} OldTrashcanMacros;

static PyObject* OldTrashcanMacros_new(PyTypeObject* type, PyObject* args, PyObject* kwds)
{
OldTrashcanMacros *self;
self = (OldTrashcanMacros*)type->tp_alloc(type, 0);
return (PyObject*)self;
}

static void OldTrashcanMacros_dealloc(OldTrashcanMacros* self)
{
PyObject_GC_UnTrack(self);
Py_TRASHCAN_SAFE_BEGIN(self)
Py_TYPE(self)->tp_free((PyObject*)self);
Py_TRASHCAN_SAFE_END(self)
}

PyTypeObject OldTrashcanMacros_Type = {
PyVarObject_HEAD_INIT(NULL,0)
"OldTrashcanMacros", /* tp_name */
(sizeof(OldTrashcanMacros)), /* tp_basicsize */
0, /* tp_itemsize */
(destructor)OldTrashcanMacros_dealloc, /* tp-dealloc */
0, /* tp_print */
0, /* tp_getattr */
0, /* tp_setattr */
0, /* tp_compare */
0, /* tp_repr */
0, /* tp_as_number */
0, /* tp_as_sequence */
0, /* tp_as_mapping */
0, /* tp_hash */
0, /* tp_call */
0, /* tp_str */
0, /* tp_getattro */
0, /* tp_setattro */
0, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC, /* tp_flags */
"Old Trashcan Macros Test", /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */
0, /* tp_richcompare */
0, /* tp_weaklistoffset */
0, /* tp_iter */
0, /* tp_iternext */
0, /* tp_methods */
0, /* tp_members */
0, /* tp_getset */
0, /* tp_base */
0, /* tp_dict */
0, /* tp_descr_get */
0, /* tp_descr_set */
0, /* tp_dictoffset */
0, /* tp_init */
0, /* tp_alloc */
OldTrashcanMacros_new, /* tp_new */
};

/* Test PEP 560 */

Expand Down Expand Up @@ -6641,6 +6702,11 @@ PyInit__testcapi(void)
Py_INCREF(&MyList_Type);
PyModule_AddObject(m, "MyList", (PyObject *)&MyList_Type);

if (PyType_Ready(&OldTrashcanMacros_Type) < 0)
return NULL;
Py_INCREF(&OldTrashcanMacros_Type);
PyModule_AddObject(m, "OldTrashcanMacros", (PyObject*)&OldTrashcanMacros_Type);

if (PyType_Ready(&MethodDescriptorBase_Type) < 0)
return NULL;
Py_INCREF(&MethodDescriptorBase_Type);
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10 changes: 10 additions & 0 deletions Objects/typeobject.c
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Expand Up @@ -1231,6 +1231,8 @@ subtype_dealloc(PyObject *self)
PyTypeObject *type, *base;
destructor basedealloc;
int has_finalizer;
PyThreadState *tstate = _PyThreadState_GET();
struct _gc_runtime_state *gcstate = &tstate->interp->gc;

/* Extract the type; we expect it to be a heap type */
type = Py_TYPE(self);
Expand Down Expand Up @@ -1283,7 +1285,11 @@ subtype_dealloc(PyObject *self)
/* UnTrack and re-Track around the trashcan macro, alas */
/* See explanation at end of function for full disclosure */
PyObject_GC_UnTrack(self);
++ tstate->trash_delete_nesting;
++ gcstate->trash_delete_nesting;
Py_TRASHCAN_BEGIN(self, subtype_dealloc);
-- tstate->trash_delete_nesting;
-- gcstate->trash_delete_nesting;

/* Find the nearest base with a different tp_dealloc */
base = type;
Expand Down Expand Up @@ -1378,7 +1384,11 @@ subtype_dealloc(PyObject *self)
Py_DECREF(type);

endlabel:
++ tstate->trash_delete_nesting;
++ gcstate->trash_delete_nesting;
Py_TRASHCAN_END
-- tstate->trash_delete_nesting;
-- gcstate->trash_delete_nesting;

/* Explanation of the weirdness around the trashcan macros:

Expand Down