bpo-36977: Make SharedMemoryManager release its resources if its parent process dies

Lib/multiprocessing/managers.py

@@ -159,6 +159,11 @@ def __init__(self, registry, address, authkey, serializer):
  self.id_to_local_proxy_obj ={}
  self.mutex = threading.Lock()
 
+ def _track_parent(self):
+ if process.parent_process() is not None:
+ process.parent_process().join()
+ self.stop_event.set()
+
  def serve_forever(self):
  '''
  Run the server forever
@@ -169,6 +174,12 @@ def serve_forever(self):
  accepter = threading.Thread(target=self.accepter)
  accepter.daemon = True
  accepter.start()
+
+ if process.parent_process() is not None:
+ watcher = threading.Thread(target=self._track_parent)
+ watcher.daemon = True
+ watcher.start()
+
  try:
  while not self.stop_event.is_set():
  self.stop_event.wait(1)

Lib/test/_test_multiprocessing.py

@@ -3824,6 +3824,45 @@ def test_shared_memory_SharedMemoryServer_ignores_sigint(self):
 
  smm.shutdown()
 
+ def test_shared_memory_SharedMemoryManager_cleanup_if_parent_dies(self):
+ # If a process that spawned a SharedMemoryManager was terminated, its
+ # manager process should notice it, unlink the resources the manager
+ # delivered, and shut down.
+ cmd = '''if 1:
+ import sys, time
+
+ from multiprocessing.managers import SharedMemoryManager
+
+
+ smm = SharedMemoryManager()
+ smm.start()
+ sl = smm.ShareableList([1, 2, 3])
+
+ sys.stdout.write(f'{sl.shm.name}\\n')
+ sys.stdout.flush()
+ time.sleep(100)
+ '''
+
+ p = subprocess.Popen([sys.executable, '-E', '-c', cmd],
+ stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+ shm_name = p.stdout.readline().decode().strip()
+ p.terminate()
+ start_time = time.monotonic()
+ deadline = start_time + 60
+ t = 0.1
+ while time.monotonic() < deadline:
+ time.sleep(t)
+ # The shared_memory segment should be released by the
+ # SharedMemoryManager server process before it shuts down.
+ try:
+ sl = shared_memory.SharedMemory(shm_name, create=False)
+ except FileNotFoundError:
+ break
+ else:
+ raise AssertionError(
+ "A SharedMemoryManager prevented some resources to be cleaned "
+ "up after its parent process was terminated")
+
  @unittest.skipIf(os.name != "posix", "resource_tracker is posix only")
  def test_shared_memory_SharedMemoryManager_reuses_resource_tracker(self):
  # bpo-36867: test that a SharedMemoryManager uses the

Misc/NEWS.d/next/Library/2019-05-20-20-56-20.bpo-36977.0Yf6-z.rst

@@ -0,0 +1 @@
+SharedMemoryManager server processes do not block anymore the release of shared memory segments if their parent process was unexpectedly terminated.