code: def notice_stream(self, stream):
          
          self._routes_by_stream[stream] = set([stream.remote_id])
          self._propagate_up(mitogen.core.ADD_ROUTE, stream.remote_id,
                          stream.name)
          mitogen.core.listen(
              obj=stream,
              name='disconnect',
              func=lambda: self._on_stream_disconnect(stream),
          )
docs: When this parent is responsible for a new directly connected child
          stream, we're also responsible for broadcasting DEL_ROUTE upstream
          if/when that child disconnects.