https://github.com/python/cpython/commit/e31d30266f33198d92e5adbbc055f6595555726d
commit: e31d30266f33198d92e5adbbc055f6595555726d
branch: main
author: Ivy Xu <[email protected]>
committer: kumaraditya303 <[email protected]>
date: 2026-07-25T13:59:59+05:30
summary:
gh-154043: Fix a data race when iterating a shared `types.GenericAlias`
iterator in FT build (#154108)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2026-07-19-19-14-39.gh-issue-154043.Kych7F.rst
M Objects/genericaliasobject.c
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2026-07-19-19-14-39.gh-issue-154043.Kych7F.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2026-07-19-19-14-39.gh-issue-154043.Kych7F.rst
new file mode 100644
index 00000000000000..d37e63e6116a59
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2026-07-19-19-14-39.gh-issue-154043.Kych7F.rst
@@ -0,0 +1,2 @@
+Fix a data race when iterating a shared :class:`types.GenericAlias` iterator
+from multiple threads under the :term:`free-threaded build`.
diff --git a/Objects/genericaliasobject.c b/Objects/genericaliasobject.c
index 71d946a637df1c..348c7dd6967a39 100644
--- a/Objects/genericaliasobject.c
+++ b/Objects/genericaliasobject.c
@@ -942,17 +942,23 @@ static PyObject *
ga_iternext(PyObject *op)
{
gaiterobject *gi = (gaiterobject*)op;
- if (gi->obj == NULL) {
+#ifdef Py_GIL_DISABLED
+ PyObject *obj = _Py_atomic_exchange_ptr(&gi->obj, NULL);
+#else
+ PyObject* obj = gi->obj;
+ gi->obj = NULL;
+#endif
+ if (obj == NULL) {
PyErr_SetNone(PyExc_StopIteration);
return NULL;
}
- gaobject *alias = (gaobject *)gi->obj;
+ gaobject *alias = (gaobject *)obj;
PyObject *starred_alias = Py_GenericAlias(alias->origin, alias->args);
+ Py_DECREF(obj);
if (starred_alias == NULL) {
return NULL;
}
((gaobject *)starred_alias)->starred = true;
- Py_SETREF(gi->obj, NULL);
return starred_alias;
}
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