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

vstinner · miss-islington · commit 2d6197190b01 · 2019-08-19T22:37:26.000Z
Add threading.Thread.__del__() method to ensure that the thread state lock is removed from the _shutdown_locks list when a thread completes. (cherry picked from commit d3dcc92) Co-authored-by: Victor Stinner <vstinner@redhat.com>
diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
@@ -757,6 +757,14 @@ def test_shutdown_locks(self):
                 # Daemon threads must never add it to _shutdown_locks.
                 self.assertNotIn(tstate_lock, threading._shutdown_locks)
 
+    def test_leak_without_join(self):
+        # bpo-37788: Test that a thread which is not joined explicitly
+        # does not leak. Test written for reference leak checks.
+        def noop(): pass
+        with support.wait_threads_exit():
+            threading.Thread(target=noop).start()
+            # Thread.join() is not called
+
 
 class ThreadJoinOnShutdown(BaseTestCase):
 
diff --git a/Lib/threading.py b/Lib/threading.py
@@ -805,6 +805,16 @@ class is implemented.
         # 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.
diff --git a/Misc/NEWS.d/next/Library/2019-08-12-17-21-10.bpo-37788.F0tR05.rst b/Misc/NEWS.d/next/Library/2019-08-12-17-21-10.bpo-37788.F0tR05.rst
@@ -0,0 +1 @@
+Fix a reference leak if a thread is not joined.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+Fix a reference leak if a thread is not joined.`