youknowone · Oct 29, 2026 · Oct 28, 2026
diff --git a/Lib/test/test_free_threading/test_grp.py b/Lib/test/test_free_threading/test_grp.py
@@ -0,0 +1,35 @@
+import unittest
+
+from test.support import import_helper, threading_helper
+from test.support.threading_helper import run_concurrently
+
+grp = import_helper.import_module("grp")
+
+from test import test_grp
+
+
+NTHREADS = 10
+
+
+@threading_helper.requires_working_threading()
+class TestGrp(unittest.TestCase):
+    def setUp(self):
+        self.test_grp = test_grp.GroupDatabaseTestCase()
+
+    def test_racing_test_values(self):
+        # test_grp.test_values() calls grp.getgrall() and checks the entries
+        run_concurrently(
+            worker_func=self.test_grp.test_values, nthreads=NTHREADS
+        )
+
+    def test_racing_test_values_extended(self):
+        # test_grp.test_values_extended() calls grp.getgrall(), grp.getgrgid(),
+        # grp.getgrnam() and checks the entries
+        run_concurrently(
+            worker_func=self.test_grp.test_values_extended,
+            nthreads=NTHREADS,
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/Lib/test/test_free_threading/test_itertools.py b/Lib/test/test_free_threading/test_itertools.py
@@ -0,0 +1,146 @@
+import unittest
+from itertools import (
+    accumulate,
+    batched,
+    chain,
+    combinations_with_replacement,
+    cycle,
+    permutations,
+    tee,
+    zip_longest,
+)
+from test.support import threading_helper
+
+
+threading_helper.requires_working_threading(module=True)
+
+
+def work_iterator(it):
+    while True:
+        try:
+            next(it)
+        except StopIteration:
+            break
+
+
+class ItertoolsThreading(unittest.TestCase):
+    @threading_helper.reap_threads
+    def test_accumulate(self):
+        number_of_iterations = 10
+        for _ in range(number_of_iterations):
+            it = accumulate(tuple(range(40)))
+            threading_helper.run_concurrently(
+                work_iterator, nthreads=10, args=[it]
+            )
+
+    @threading_helper.reap_threads
+    def test_batched(self):
+        number_of_iterations = 10
+        for _ in range(number_of_iterations):
+            it = batched(tuple(range(1000)), 2)
+            threading_helper.run_concurrently(
+                work_iterator, nthreads=10, args=[it]
+            )
+
+    @threading_helper.reap_threads
+    def test_cycle(self):
+        def work(it):
+            for _ in range(400):
+                next(it)
+
+        number_of_iterations = 6
+        for _ in range(number_of_iterations):
+            it = cycle((1, 2, 3, 4))
+            threading_helper.run_concurrently(work, nthreads=6, args=[it])
+
+    @threading_helper.reap_threads
+    def test_chain(self):
+        number_of_iterations = 10
+        for _ in range(number_of_iterations):
+            it = chain(*[(1,)] * 200)
+            threading_helper.run_concurrently(
+                work_iterator, nthreads=6, args=[it]
+            )
+
+    @threading_helper.reap_threads
+    def test_combinations_with_replacement(self):
+        number_of_iterations = 6
+        for _ in range(number_of_iterations):
+            it = combinations_with_replacement(tuple(range(2)), 2)
+            threading_helper.run_concurrently(
+                work_iterator, nthreads=6, args=[it]
+            )
+
+    @threading_helper.reap_threads
+    def test_permutations(self):
+        number_of_iterations = 6
+        for _ in range(number_of_iterations):
+            it = permutations(tuple(range(4)), 2)
+            threading_helper.run_concurrently(
+                work_iterator, nthreads=6, args=[it]
+            )
+
+    @threading_helper.reap_threads
+    def test_zip_longest(self):
+        number_of_iterations = 10
+        for _ in range(number_of_iterations):
+            it = zip_longest(list(range(4)), list(range(8)), fillvalue=0)
+            threading_helper.run_concurrently(
+                work_iterator, nthreads=10, args=[it]
+            )
+
+
+class TestTeeConcurrent(unittest.TestCase):
+    # itertools.tee branches share a linked list of internal data cells.
+    # Concurrent iteration must not corrupt that shared state or crash the
+    # free-threaded build.  A crash shows up as the interpreter dying (not as a
+    # caught exception); tee is documented as not thread-safe, so a
+    # ``RuntimeError`` from the re-entrancy guard is an allowed outcome and is
+    # tolerated here.
+
+    def test_same_branch(self):
+        # Many threads consume the same tee branch.
+        errors = []
+
+        def consume(it):
+            try:
+                for _ in it:
+                    pass
+            except RuntimeError:
+                pass
+            except Exception as e:
+                errors.append(e)
+
+        for _ in range(100):
+            a, _ = tee(iter(range(2000)), 2)
+            threading_helper.run_concurrently(consume, nthreads=8, args=(a,))
+
+        self.assertEqual(errors, [], msg=f"unexpected errors: {errors}")
+
+    def test_sibling_branches(self):
+        # Each thread consumes a different sibling branch of the same tee.
+        errors = []
+
+        def make_worker(it):
+            def consume():
+                try:
+                    for _ in it:
+                        pass
+                except RuntimeError:
+                    pass
+                except Exception as e:
+                    errors.append(e)
+
+            return consume
+
+        for _ in range(100):
+            branches = tee(iter(range(4000)), 8)
+            threading_helper.run_concurrently(
+                [make_worker(it) for it in branches]
+            )
+
+        self.assertEqual(errors, [], msg=f"unexpected errors: {errors}")
+
+
+if __name__ == "__main__":
+    unittest.main()