docs: async def _process_message(self, message):
          """
          Adds the given message to the list of messages that must be
          acknowledged and dispatches control to different ``_handle_*``
          method based on its type.
          """
          self._pending_ack.add(message.msg_id)
          handler = self._handlers.get(message.obj.CONSTRUCTOR_ID,
                                       self._handle_update)
          await handler(message)