message: Running session.close if coordinator can't kill all threads.
diff: @@ -66,6 +66,9 @@ def QueueRunners(session):
  yield
  finally:
  coord.request_stop()
  + try:
  coord.join(threads, stop_grace_period_secs=120)
  + except RuntimeError:
  + session.close()
  _queue_runner_lock.release()
  