:type span_datas: list of :class:
            `~opencensus.trace.span_data.SpanData`
        :param list of opencensus.trace.span_data.SpanData span_datas:
            SpanData tuples to emit

def emit(self, span_datas):
        """
        :type span_datas: list of :class:
            `~opencensus.trace.span_data.SpanData`
        :param list of opencensus.trace.span_data.SpanData span_datas:
            SpanData tuples to emit
        """

        try:

            # TODO: keep the stream alive.
            # The stream is terminated after iteration completes.
            # To keep it alive, we can enqueue proto spans here
            # and asyncronously read them and send to the agent.
            responses = self.client.Export(
                self.generate_span_requests(span_datas))

            # read response
            for _ in responses:
                pass

        except grpc.RpcError:
            pass