code: def put(self, message):
      
      with self._outgoing_lock:
        self._outgoing.append(message)
        self._outgoing_counter += 1
  
        # Check to see if there are pending queues waiting for the item.
        if self._outgoing_counter in self._outgoing_pending_queues:
          for q in self._outgoing_pending_queues[self._outgoing_counter]:
            q.put(message)
          del self._outgoing_pending_queues[self._outgoing_counter]
docs: Put a message into the outgoing message stack.
  
      Outgoing message will be stored indefinitely to support multi-users.