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[3.14] gh-129069: fix more thread safety issues in list (GH-143019) #158488

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[3.14] gh-129069: fix more thread safety issues in list (GH-143019) #158488

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[3.14] gh-129069: fix more thread safety issues in list (GH-143019) 
(cherry picked from commit 487e91c)

Co-authored-by: Kumar Aditya <kumaraditya@python.org>
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@KRRT7 @kumaraditya303
KRRT7 and kumaraditya303 committed Sep 30, 2026
commit fca6e412ece727f5e77fef0dfbe251baaa155f43
58 changes: 58 additions & 0 deletions Lib/test/test_free_threading/test_list.py
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Original file line number Diff line number Diff line change
Expand Up @@ -112,6 +112,64 @@ def size_function():
with threading_helper.start_threads(threads):
pass

def test_reverse(self):
def reverse_list(b, l):
b.wait()
for _ in range(100):
l.reverse()

def reader_list(b, l):
b.wait()
for _ in range(100):
for i in range(10):
self.assertTrue(0 <= l[i] < 10)

l = list(range(10))
barrier = Barrier(2)
threads = [Thread(target=reverse_list, args=(barrier, l)),
Thread(target=reader_list, args=(barrier, l))]
with threading_helper.start_threads(threads):
pass

def test_slice_assignment1(self):
def assign_slice(b, l):
b.wait()
for _ in range(100):
l[2:5] = [7, 8, 9]

def reader_list(b, l):
b.wait()
for _ in range(100):
self.assertIn(l[2], (2, 7))
self.assertIn(l[3], (3, 8))
self.assertIn(l[4], (4, 9))

l = list(range(10))
barrier = Barrier(2)
threads = [Thread(target=assign_slice, args=(barrier, l)),
Thread(target=reader_list, args=(barrier, l))]
with threading_helper.start_threads(threads):
pass

def test_slice_assignment2(self):
def assign_slice(b, l):
b.wait()
for _ in range(100):
l[::2] = [10, 11, 12, 13, 14]

def reader_list(b, l):
b.wait()
for _ in range(100):
for i in range(0, 10, 2):
self.assertIn(l[i], (i, 10 + i // 2))

l = list(range(10))
barrier = Barrier(2)
threads = [Thread(target=assign_slice, args=(barrier, l)),
Thread(target=reader_list, args=(barrier, l))]
with threading_helper.start_threads(threads):
pass


if __name__ == "__main__":
unittest.main()
10 changes: 5 additions & 5 deletions Objects/listobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -495,7 +495,7 @@ ins1(PyListObject *self, Py_ssize_t where, PyObject *v)
where = n;
items = self->ob_item;
for (i = n; --i >= where; )
FT_ATOMIC_STORE_PTR_RELAXED(items[i+1], items[i]);
FT_ATOMIC_STORE_PTR_RELEASE(items[i+1], items[i]);
FT_ATOMIC_STORE_PTR_RELEASE(items[where], Py_NewRef(v));
return 0;
}
Expand Down Expand Up @@ -1091,7 +1091,7 @@ list_ass_item_lock_held(PyListObject *a, Py_ssize_t i, PyObject *v)
if (v == NULL) {
Py_ssize_t size = Py_SIZE(a);
for (Py_ssize_t idx = i; idx < size - 1; idx++) {
FT_ATOMIC_STORE_PTR_RELAXED(a->ob_item[idx], a->ob_item[idx + 1]);
FT_ATOMIC_STORE_PTR_RELEASE(a->ob_item[idx], a->ob_item[idx + 1]);
}
Py_SET_SIZE(a, size - 1);
}
Expand Down Expand Up @@ -1580,8 +1580,8 @@ reverse_slice(PyObject **lo, PyObject **hi)
--hi;
while (lo < hi) {
PyObject *t = *lo;
*lo = *hi;
*hi = t;
FT_ATOMIC_STORE_PTR_RELEASE(*lo, *hi);
FT_ATOMIC_STORE_PTR_RELEASE(*hi, t);
++lo;
--hi;
}
Expand Down Expand Up @@ -3832,7 +3832,7 @@ list_ass_subscript_lock_held(PyObject *_self, PyObject *item, PyObject *value)
cur += (size_t)step, i++) {
garbage[i] = selfitems[cur];
ins = Py_NewRef(seqitems[i]);
selfitems[cur] = ins;
FT_ATOMIC_STORE_PTR_RELEASE(selfitems[cur], ins);
}

for (i = 0; i < slicelength; i++) {
Expand Down
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