def _flush(self):
        """
        Flush the write buffers of the stream if applicable.

        In write mode, send the buffer content to the cloud object.
        """
        # Flush buffer to specified range
        buffer = self._get_buffer()
        start = self._buffer_size * (self._seek - 1)
        end = start + len(buffer)

        future = self._workers.submit(
            self._flush_range, buffer=buffer, start=start, end=end)
        self._write_futures.append(future)
        future.add_done_callback(partial(self._update_size, end))
Flush the write buffers of the stream if applicable.

        In write mode, send the buffer content to the cloud object.