code: func (d *deadlineTimer) SetWriteDeadline(t time.Time) error {
  	d.mu.Lock()
  	d.setDeadline(&d.writeCancelCh, &d.writeTimer, t)
  	d.mu.Unlock()
  	return nil
  }
docs: // SetWriteDeadline implements net.Conn.SetWriteDeadline and
  // net.PacketConn.SetWriteDeadline.