docs: def _flush(self):
          """
          Flush the write buffers of the stream.
          """
          # Upload segment with workers
          name = self._segment_name % self._seek
          response = self._workers.submit(
              self._client.put_object, self._container, name,
              self._get_buffer())
  
          # Save segment information in manifest
          self._write_futures.append(dict(
              etag=response, path='/'.join((self._container, name))))