Add a test.

Author: ZeroIntensity

Lib/test/test_threading.py

@@ -1039,6 +1039,22 @@ def checker():
         self.assertEqual(threading.gettrace(), old_trace)
         self.assertEqual(sys.gettrace(), old_trace)
 
+    @unittest.skipUnless(support.Py_GIL_DISABLED, "only meaningful under free-threading")
+    def test_settrace_all_threads_race(self):
+        # GH-132296: settrace_all_threads() could be racy on the free-threaded build
+        #if the threads were concurrently deleted.
+        def dummy(*args):
+            pass
+
+        def do_settrace():
+            threading.settrace_all_threads(dummy)
+
+        with threading_helper.catch_threading_exception() as cm:
+            with threading_helper.start_threads((threading.Thread(target=do_settrace) for _ in range(8))):
+                pass
+
+            self.assertIsNone(cm.exc_value)
+
     def test_getprofile(self):
         def fn(*args): pass
         old_profile = threading.getprofile()