https://github.com/python/cpython/commit/54024655ae7490b18fe36e6e38839b95edbfa471
commit: 54024655ae7490b18fe36e6e38839b95edbfa471
branch: 3.14
author: Sam Gross <[email protected]>
committer: colesbury <[email protected]>
date: 2026-03-10T09:31:52-04:00
summary:
[3.14] gh-145685: Stop the world when updating MRO of existing types
(gh-145707) (#145715)
We already have a stop-the-world pause elsewhere in this code path
(type_set_bases) and this makes will make it easier to avoid contention
on the TYPE_LOCK when looking up names in the MRO hierarchy.
Also use deferred reference counting for non-immortal MROs.
(cherry picked from commit 0b65c88c2af6e09530a9aa21800771aa687371db)
files:
M Objects/typeobject.c
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 76886a18036854..8d7392f3544368 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -76,6 +76,62 @@ class object "PyObject *" "&PyBaseObject_Type"
#define ASSERT_TYPE_LOCK_HELD() \
_Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(TYPE_LOCK)
+static void
+types_stop_world(void)
+{
+ PyInterpreterState *interp = _PyInterpreterState_GET();
+ _PyEval_StopTheWorld(interp);
+}
+
+static void
+types_start_world(void)
+{
+ PyInterpreterState *interp = _PyInterpreterState_GET();
+ _PyEval_StartTheWorld(interp);
+}
+
+// This is used to temporarily prevent the TYPE_LOCK from being suspended
+// when held by the topmost critical section.
+static void
+type_lock_prevent_release(void)
+{
+ PyThreadState *tstate = _PyThreadState_GET();
+ uintptr_t *tagptr = &tstate->critical_section;
+ PyCriticalSection *c = (PyCriticalSection *)(*tagptr &
~_Py_CRITICAL_SECTION_MASK);
+ if (!(*tagptr & _Py_CRITICAL_SECTION_TWO_MUTEXES)) {
+ assert(c->_cs_mutex == TYPE_LOCK);
+ c->_cs_mutex = NULL;
+ }
+ else {
+ PyCriticalSection2 *c2 = (PyCriticalSection2 *)c;
+ if (c->_cs_mutex == TYPE_LOCK) {
+ c->_cs_mutex = c2->_cs_mutex2;
+ c2->_cs_mutex2 = NULL;
+ }
+ else {
+ assert(c2->_cs_mutex2 == TYPE_LOCK);
+ c2->_cs_mutex2 = NULL;
+ }
+ }
+}
+
+static void
+type_lock_allow_release(void)
+{
+ PyThreadState *tstate = _PyThreadState_GET();
+ uintptr_t *tagptr = &tstate->critical_section;
+ PyCriticalSection *c = (PyCriticalSection *)(*tagptr &
~_Py_CRITICAL_SECTION_MASK);
+ if (!(*tagptr & _Py_CRITICAL_SECTION_TWO_MUTEXES)) {
+ assert(c->_cs_mutex == NULL);
+ c->_cs_mutex = TYPE_LOCK;
+ }
+ else {
+ PyCriticalSection2 *c2 = (PyCriticalSection2 *)c;
+ assert(c2->_cs_mutex2 == NULL);
+ c2->_cs_mutex2 = TYPE_LOCK;
+ }
+}
+
#else
#define BEGIN_TYPE_LOCK()
@@ -83,6 +139,10 @@ class object "PyObject *" "&PyBaseObject_Type"
#define BEGIN_TYPE_DICT_LOCK(d)
#define END_TYPE_DICT_LOCK()
#define ASSERT_TYPE_LOCK_HELD()
+#define types_stop_world()
+#define types_start_world()
+#define type_lock_prevent_release()
+#define type_lock_allow_release()
#endif
@@ -541,7 +601,6 @@ clear_tp_bases(PyTypeObject *self, int final)
static inline PyObject *
lookup_tp_mro(PyTypeObject *self)
{
- ASSERT_TYPE_LOCK_HELD();
return self->tp_mro;
}
@@ -580,8 +639,19 @@ set_tp_mro(PyTypeObject *self, PyObject *mro, int initial)
/* Other checks are done via set_tp_bases. */
_Py_SetImmortal(mro);
}
+ else {
+ PyUnstable_Object_EnableDeferredRefcount(mro);
+ }
+ }
+ if (!initial) {
+ type_lock_prevent_release();
+ types_stop_world();
}
self->tp_mro = mro;
+ if (!initial) {
+ types_start_world();
+ type_lock_allow_release();
+ }
}
static inline void
@@ -1627,18 +1697,11 @@ static PyObject *
type_get_mro(PyObject *tp, void *Py_UNUSED(closure))
{
PyTypeObject *type = PyTypeObject_CAST(tp);
- PyObject *mro;
-
- BEGIN_TYPE_LOCK();
- mro = lookup_tp_mro(type);
+ PyObject *mro = lookup_tp_mro(type);
if (mro == NULL) {
- mro = Py_None;
- } else {
- Py_INCREF(mro);
+ Py_RETURN_NONE;
}
-
- END_TYPE_LOCK();
- return mro;
+ return Py_NewRef(mro);
}
static PyTypeObject *best_base(PyObject *);
_______________________________________________
Python-checkins mailing list -- [email protected]
To unsubscribe send an email to [email protected]
https://mail.python.org/mailman3//lists/python-checkins.python.org
Member address: [email protected]
