func (p *Pinger) RunLoop() {
	p.mu.Lock()
	p.ctx = newContext()
	p.mu.Unlock()
	go p.run(false)
}
func (p *Pinger) RunLoop() {
	p.mu.Lock()
	p.ctx = newContext()
	p.mu.Unlock()
	go p.run(false)
}
// RunLoop invokes send/receive procedure repeatedly. It sends packets to all
// hosts which have already been added by AddIP() etc. and wait those responses.
// When it receives a response, it calls "receive" handler registered by
// AddHander(). After MaxRTT seconds, it calls "idle" handler, resend packets
// and wait those response. MaxRTT works as an interval time.
//
// This is a non-blocking method so immediately returns. If you want to monitor
// and stop sending packets, use Done() and Stop() methods. For example,
//
//	p.RunLoop()
//	ticker := time.NewTicker(time.Millisecond * 250)
//	select {
//	case <-p.Done():
//		if err := p.Err(); err != nil {
//			log.Fatalf("Ping failed: %v", err)
//		}
//	case <-ticker.C:
//		break
//	}
//	ticker.Stop()
//	p.Stop()
//
// For more details, please see "cmd/ping/ping.go".