[3.10] bpo-37788: Fix reference leak when Thread is never joined (GH-26103) (GH-26138)
When a Thread is not joined after it has stopped, its lock may remain in the _shutdown_locks set until interpreter shutdown. If many threads are created this way, the _shutdown_locks set could therefore grow endlessly. To avoid such a situation, purge expired locks each time a new one is added or removed.
(cherry picked from commit c10c2ec7a0e06975e8010c56c9c3270f8ea322ec)
Co-authored-by: Antoine Pitrou <antoine@python.org>
diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
index 546773e..08c0ccd 100644
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -907,6 +907,13 @@ def __call__(self):
thread.join()
self.assertTrue(target.ran)
+ 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 threading_helper.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
index fb70abd..6c3d49c 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -780,12 +780,27 @@ def _newname(name_template):
_active = {} # maps thread id to Thread object
_limbo = {}
_dangling = WeakSet()
+
# Set of Thread._tstate_lock locks of non-daemon threads used by _shutdown()
# to wait until all Python thread states get deleted:
# see Thread._set_tstate_lock().
_shutdown_locks_lock = _allocate_lock()
_shutdown_locks = set()
+def _maintain_shutdown_locks():
+ """
+ Drop any shutdown locks that don't correspond to running threads anymore.
+
+ Calling this from time to time avoids an ever-growing _shutdown_locks
+ set when Thread objects are not joined explicitly. See bpo-37788.
+
+ This must be called with _shutdown_locks_lock acquired.
+ """
+ # If a lock was released, the corresponding thread has exited
+ to_remove = [lock for lock in _shutdown_locks if not lock.locked()]
+ _shutdown_locks.difference_update(to_remove)
+
+
# Main class for threads
class Thread:
@@ -968,6 +983,7 @@ def _set_tstate_lock(self):
if not self.daemon:
with _shutdown_locks_lock:
+ _maintain_shutdown_locks()
_shutdown_locks.add(self._tstate_lock)
def _bootstrap_inner(self):
@@ -1023,7 +1039,8 @@ def _stop(self):
self._tstate_lock = None
if not self.daemon:
with _shutdown_locks_lock:
- _shutdown_locks.discard(lock)
+ # Remove our lock and other released locks from _shutdown_locks
+ _maintain_shutdown_locks()
def _delete(self):
"Remove current thread from the dict of currently running threads."