[3.12] gh-110167: Fix test_socket deadlock in doCleanups() (GH-110416)

Lib/test/test_socket.py

@@ -218,8 +218,13 @@ def setUp(self):
 class ThreadSafeCleanupTestCase:
     """Subclass of unittest.TestCase with thread-safe cleanup methods.
 
-    This subclass protects the addCleanup() and doCleanups() methods
-    with a recursive lock.
+    This subclass protects the addCleanup() method with a recursive lock.
+
+    doCleanups() is called when the server completed, but the client can still
+    be running in its thread especially if the server failed with a timeout.
+    Don't put a lock on doCleanups() to prevent deadlock between addCleanup()
+    called in the client and doCleanups() waiting for self.done.wait of
+    ThreadableTest._setUp() (gh-110167)
     """
 
     def __init__(self, *args, **kwargs):
@@ -230,9 +235,6 @@ def addCleanup(self, *args, **kwargs):
         with self._cleanup_lock:
             return super().addCleanup(*args, **kwargs)
 
-    def doCleanups(self, *args, **kwargs):
-        with self._cleanup_lock:
-            return super().doCleanups(*args, **kwargs)
 
 class SocketCANTest(unittest.TestCase):
 

Misc/NEWS.d/next/Tests/2023-10-05-19-33-49.gh-issue-110167.mIdj3v.rst

@@ -0,0 +1,5 @@
+Fix a deadlock in test_socket when server fails with a timeout but the
+client is still running in its thread. Don't hold a lock to call cleanup
+functions in doCleanups(). One of the cleanup function waits until the
+client completes, whereas the client could deadlock if it called
+addCleanup() in such situation. Patch by Victor Stinner.