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