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

Sun May 26 10:25:53 EDT 2019

https://github.com/python/cpython/commit/180dc1b0f4a57c3f66351568ae8488fa8576d7f0
commit: 180dc1b0f4a57c3f66351568ae8488fa8576d7f0
branch: master
author: Julien Palard <julien at palard.fr>
committer: Mark Shannon <mark at hotpy.org>
date: 2019年05月26日T15:25:47+01:00
summary:
bpo-28866: No type cache for types with specialized mro, invalidation is hard. (#13157)
* No type cache for types with specialized mro, invalidation is hard.
* FIX: Don't disable method cache custom types that do not implement mro().
* fixing implem.
* Avoid storing error flags, also decref.
* news entry
* Clear as soon as we're getting an error.
* FIX: Reference leak.
files:
A Misc/NEWS.d/next/Core and Builtins/2019-05-08-16-36-51.bpo-28866.qCv_bj.rst
M Objects/typeobject.c

diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-05-08-16-36-51.bpo-28866.qCv_bj.rst b/Misc/NEWS.d/next/Core and Builtins/2019-05-08-16-36-51.bpo-28866.qCv_bj.rst
new file mode 100644
index 000000000000..69017293649c
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2019-05-08-16-36-51.bpo-28866.qCv_bj.rst	
@@ -0,0 +1,2 @@
+Avoid caching attributes of classes which type defines mro() to avoid a hard
+cache invalidation problem.
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 339f7285292c..fc809d36e10b 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -78,6 +78,9 @@ 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 '('.
@@ -287,17 +290,35 @@ 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);
@@ -308,14 +329,15 @@ 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
