pythongh-130522: Fix unraisable TypeError in threading at interpreter shutdown (python#131537)

Co-authored-by: Peter Bierma <[email protected]>

Author: 2 people

Lib/test/test_threading.py

@@ -2042,6 +2042,23 @@ def modify_file():
             t.start()
             t.join()
 
+    def test_dummy_thread_on_interpreter_shutdown(self):
+        # GH-130522: When `threading` held a reference to itself and then a
+        # _DummyThread() object was created, destruction of the dummy thread
+        # would emit an unraisable exception at shutdown, due to a lock being
+        # destroyed.
+        code = """if True:
+        import sys
+        import threading
+
+        threading.x = sys.modules[__name__]
+        x = threading._DummyThread()
+        """
+        rc, out, err = assert_python_ok("-c", code)
+        self.assertEqual(rc, 0)
+        self.assertEqual(out, b"")
+        self.assertEqual(err, b"")
+
 
 class ThreadRunFail(threading.Thread):
     def run(self):

Lib/threading.py

@@ -1414,7 +1414,7 @@ def __init__(self, dummy_thread):
         # the related _DummyThread will be kept forever!
         _thread_local_info._track_dummy_thread_ref = self
 
-    def __del__(self):
+    def __del__(self, _active_limbo_lock=_active_limbo_lock, _active=_active):
         with _active_limbo_lock:
             if _active.get(self._tident) is self._dummy_thread:
                 _active.pop(self._tident, None)

Misc/NEWS.d/next/Library/2025-07-25-09-21-56.gh-issue-130522.Crwq68.rst

@@ -0,0 +1,2 @@
+Fix unraisable :exc:`TypeError` raised during :term:`interpreter shutdown`
+in the :mod:`threading` module.