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gh-131586: Avoid refcount contention in context managers (gh-131851)

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This avoid reference count contention in the free threading build
when calling special methods like `__enter__` and `__exit__`.
This commit is contained in:
Sam Gross
2025-04-21 15:54:25 -04:00
committed by GitHub
parent 8dfa840773
commit da53660f35
11 changed files with 247 additions and 207 deletions
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43
Objects/typeobject.c
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@@ -2794,32 +2794,37 @@ _PyObject_LookupSpecial(PyObject *self, PyObject *attr)
return res;
}
/* Steals a reference to self */
PyObject *
_PyObject_LookupSpecialMethod(PyObject *self, PyObject *attr, PyObject **self_or_null)
// Lookup the method name `attr` on `self`. On entry, `method_and_self[0]`
// is null and `method_and_self[1]` is `self`. On exit, `method_and_self[0]`
// is the method object and `method_and_self[1]` is `self` if the method is
// not bound.
// Return 1 on success, -1 on error, and 0 if the method is missing.
int
_PyObject_LookupSpecialMethod(PyObject *attr, _PyStackRef *method_and_self)
{
PyObject *res;
res = _PyType_LookupRef(Py_TYPE(self), attr);
if (res == NULL) {
Py_DECREF(self);
*self_or_null = NULL;
return NULL;
PyObject *self = PyStackRef_AsPyObjectBorrow(method_and_self[1]);
_PyType_LookupStackRefAndVersion(Py_TYPE(self), attr, &method_and_self[0]);
PyObject *method_o = PyStackRef_AsPyObjectBorrow(method_and_self[0]);
if (method_o == NULL) {
return 0;
}
if (_PyType_HasFeature(Py_TYPE(res), Py_TPFLAGS_METHOD_DESCRIPTOR)) {
if (_PyType_HasFeature(Py_TYPE(method_o), Py_TPFLAGS_METHOD_DESCRIPTOR)) {
/* Avoid temporary PyMethodObject */
*self_or_null = self;
return 1;
}
else {
descrgetfunc f = Py_TYPE(res)->tp_descr_get;
if (f != NULL) {
Py_SETREF(res, f(res, self, (PyObject *)(Py_TYPE(self))));
descrgetfunc f = Py_TYPE(method_o)->tp_descr_get;
if (f != NULL) {
PyObject *func = f(method_o, self, (PyObject *)(Py_TYPE(self)));
if (func == NULL) {
return -1;
}
*self_or_null = NULL;
Py_DECREF(self);
PyStackRef_CLEAR(method_and_self[0]); // clear method
method_and_self[0] = PyStackRef_FromPyObjectSteal(func);
}
return res;
PyStackRef_CLEAR(method_and_self[1]); // clear self
return 1;
}
static int