bpo-42350: Fix Thread._reset_internal_locks() (GH-23268)

Fix the threading.Thread class at fork: do nothing if the thread is
already stopped (ex: fork called at Python exit). Previously, an
error was logged in the child process.

1 files changed, 6 insertions, 2 deletions

diff --git a/Lib/threading.py b/Lib/threading.py
index 7dae77dfd4..7b3d63dd21 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -844,8 +844,12 @@ class Thread:
         # they may be in an invalid state leading to a deadlock or crash.
         self._started._at_fork_reinit()
         if is_alive:
-            self._tstate_lock._at_fork_reinit()
-            self._tstate_lock.acquire()
+            # bpo-42350: If the fork happens when the thread is already stopped
+            # (ex: after threading._shutdown() has been called), _tstate_lock
+            # is None. Do nothing in this case.
+            if self._tstate_lock is not None:
+                self._tstate_lock._at_fork_reinit()
+                self._tstate_lock.acquire()
         else:
             # The thread isn't alive after fork: it doesn't have a tstate
             # anymore.