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gh-154043: Fix a data race when iterating a shared types.GenericAlias iterator in FT build #154108

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gh-154043: Fix a data race when iterating a shared types.GenericAlias iterator in FT build #154108

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0fc508e
Fix a data race when iterating a shared types.GenericAlias iterator
ByteFlowing1337 Jul 19, 2026
8f2d85e
Move test to `test_types.py`
ByteFlowing1337 Jul 20, 2026
24cd9d8
Address review
ByteFlowing1337 Jul 21, 2026
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-07-19-19-14-39.gh-issue-154043.Kych7F.rst
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Original file line number Diff line number Diff line change
@@ -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`.
12 changes: 9 additions & 3 deletions Objects/genericaliasobject.c
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Expand Up @@ -939,17 +939,23 @@ 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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