https://github.com/python/cpython/commit/68abf17fa926db94dc17f01a7095bdcee2a52314
commit: 68abf17fa926db94dc17f01a7095bdcee2a52314
branch: main
author: sobolevn <[email protected]>
committer: sobolevn <[email protected]>
date: 2026-07-08T17:57:22+03:00
summary:
gh-153298: Fix data race in `GenericAlias` parameter initialization on FT
(#153318)
files:
A Lib/test/test_free_threading/test_types.py
A
Misc/NEWS.d/next/Core_and_Builtins/2026-07-08-13-23-11.gh-issue-153298.wvcXxN.rst
M Objects/genericaliasobject.c
diff --git a/Lib/test/test_free_threading/test_types.py
b/Lib/test/test_free_threading/test_types.py
new file mode 100644
index 000000000000000..76fcf1590122f54
--- /dev/null
+++ b/Lib/test/test_free_threading/test_types.py
@@ -0,0 +1,33 @@
+import unittest
+from typing import TypeVar
+from test.support import threading_helper
+
+threading_helper.requires_working_threading(module=True)
+
+
+class TestGenericAlias(unittest.TestCase):
+ def test_parameters_race(self):
+ # gh-153298
+
+ T = TypeVar('T')
+ slot = [list[T]]
+
+ def access():
+ for _ in range(2000):
+ try:
+ _ = slot[0].__parameters__
+ except Exception:
+ pass
+
+ def refresh():
+ for _ in range(2000):
+ slot[0] = list[T]
+
+ threading_helper.run_concurrently([
+ *[access for _ in range(6)],
+ *[refresh for _ in range(2)],
+ ])
+
+
+if __name__ == "__main__":
+ unittest.main()
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2026-07-08-13-23-11.gh-issue-153298.wvcXxN.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2026-07-08-13-23-11.gh-issue-153298.wvcXxN.rst
new file mode 100644
index 000000000000000..38d548834d5e02e
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2026-07-08-13-23-11.gh-issue-153298.wvcXxN.rst
@@ -0,0 +1,2 @@
+Fixes a data race in :class:`types.GenericAlias` ``__parameters__``
+initialization on free-threading builds.
diff --git a/Objects/genericaliasobject.c b/Objects/genericaliasobject.c
index c2083e6fcb77f47..4e85927def7ea78 100644
--- a/Objects/genericaliasobject.c
+++ b/Objects/genericaliasobject.c
@@ -841,7 +841,7 @@ static PyMemberDef ga_members[] = {
};
static PyObject *
-ga_parameters(PyObject *self, void *unused)
+ga_parameters_lock_held(PyObject *self)
{
gaobject *alias = (gaobject *)self;
if (alias->parameters == NULL) {
@@ -853,6 +853,16 @@ ga_parameters(PyObject *self, void *unused)
return Py_NewRef(alias->parameters);
}
+static PyObject *
+ga_parameters(PyObject *self, void *unused)
+{
+ PyObject *result;
+ Py_BEGIN_CRITICAL_SECTION(self);
+ result = ga_parameters_lock_held(self);
+ Py_END_CRITICAL_SECTION();
+ return result;
+}
+
static PyObject *
ga_unpacked_tuple_args(PyObject *self, void *unused)
{
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