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[3.7] bpo-28866: No type cache for types with specialized mro, invalidation is hard. (GH-13157) #13589

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May 26, 2019
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[3.7] bpo-28866: No type cache for types with specialized mro, invalidation is hard. (GH-13157) #13589

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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2019-05-08-16-36-51.bpo-28866.qCv_bj.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Avoid caching attributes of classes which type defines mro() to avoid a hard
cache invalidation problem.
38 changes: 30 additions & 8 deletions Objects/typeobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,9 @@ slot_tp_new(PyTypeObject *type, PyObject *args, PyObject *kwds);
static void
clear_slotdefs(void);

static PyObject *
lookup_maybe_method(PyObject *self, _Py_Identifier *attrid, int *unbound);

/*
* finds the beginning of the docstring's introspection signature.
* if present, returns a pointer pointing to the first '('.
Expand Down Expand Up @@ -281,17 +284,35 @@ type_mro_modified(PyTypeObject *type, PyObject *bases) {

Unset HAVE_VERSION_TAG and VALID_VERSION_TAG if the type
has a custom MRO that includes a type which is not officially
super type.
super type, or if the type implements its own mro() method.

Called from mro_internal, which will subsequently be called on
each subclass when their mro is recursively updated.
*/
Py_ssize_t i, n;
int clear = 0;
int custom = (Py_TYPE(type) != &PyType_Type);
int unbound;
PyObject *mro_meth = NULL;
PyObject *type_mro_meth = NULL;

if (!PyType_HasFeature(type, Py_TPFLAGS_HAVE_VERSION_TAG))
return;

if (custom) {
_Py_IDENTIFIER(mro);
mro_meth = lookup_maybe_method(
(PyObject *)type, &PyId_mro, &unbound);
if (mro_meth == NULL)
goto clear;
type_mro_meth = lookup_maybe_method(
(PyObject *)&PyType_Type, &PyId_mro, &unbound);
if (type_mro_meth == NULL)
goto clear;
if (mro_meth != type_mro_meth)
goto clear;
Py_XDECREF(mro_meth);
Py_XDECREF(type_mro_meth);
}
n = PyTuple_GET_SIZE(bases);
for (i = 0; i < n; i++) {
PyObject *b = PyTuple_GET_ITEM(bases, i);
Expand All @@ -302,14 +323,15 @@ type_mro_modified(PyTypeObject *type, PyObject *bases) {

if (!PyType_HasFeature(cls, Py_TPFLAGS_HAVE_VERSION_TAG) ||
!PyType_IsSubtype(type, cls)) {
clear = 1;
break;
goto clear;
}
}

if (clear)
type->tp_flags &= ~(Py_TPFLAGS_HAVE_VERSION_TAG|
Py_TPFLAGS_VALID_VERSION_TAG);
return;
clear:
Py_XDECREF(mro_meth);
Py_XDECREF(type_mro_meth);
type->tp_flags &= ~(Py_TPFLAGS_HAVE_VERSION_TAG|
Py_TPFLAGS_VALID_VERSION_TAG);
}

static int
Expand Down