bpo-37788: Fix a reference leak if a thread is not joined (GH-15228)

Add threading.Thread.__del__() method to ensure that the thread state
lock is removed from the _shutdown_locks list when a thread
completes.

1 files changed, 10 insertions, 0 deletions

diff --git a/Lib/threading.py b/Lib/threading.py
index 32a3d7c..67e1c4f 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -806,6 +806,16 @@ class Thread:
         # For debugging and _after_fork()
         _dangling.add(self)
 
+    def __del__(self):
+        if not self._initialized:
+            return
+        lock = self._tstate_lock
+        if lock is not None and not self.daemon:
+            # ensure that self._tstate_lock is not in _shutdown_locks
+            # if join() was not called explicitly
+            with _shutdown_locks_lock:
+                _shutdown_locks.discard(lock)
+
     def _reset_internal_locks(self, is_alive):
         # private!  Called by _after_fork() to reset our internal locks as
         # they may be in an invalid state leading to a deadlock or crash.