if you run many goroutine some goroutine will be a deadlock

[goofy-z]

i have study golang for only 3 weeks i can not solve this problem

1. if someone can help me to find out the reason why my program will block;
2. i do many goroutine it has some wrong result ,some ip can ping right but pinger.PacketsRecv = 0
   

i tried to find the reason, and i got some message

var wg sync.WaitGroup
recv := make(chan *packet, 5)
defer close(recv)
wg.Add(1)
go p.recvICMP(conn, recv, &wg)
err := p.sendICMP(conn)
if err != nil {
	fmt.Println(err.Error())
}
    timeout := time.NewTicker(p.Timeout)
defer timeout.Stop()
interval := time.NewTicker(p.Interval)
defer interval.Stop()

for {
	select {
	case <-p.done:
		wg.Wait()
		return
	case <-timeout.C:
		close(p.done)
		wg.Wait()
		return
	case <-interval.C:
		if p.Count > 0 && p.PacketsSent >= p.Count {
			continue
		}
		err = p.sendICMP(conn)
		if err != nil {
			fmt.Println("FATAL: ", err.Error())
		}
	case r := <-recv:
		err := p.processPacket(r)
		if err != nil {
			fmt.Println("FATAL: ", err.Error())
		}
	}
	if p.Count > 0 && p.PacketsRecv >= p.Count {
		close(p.done)
		wg.Wait()
		return
	}
}

i need to ping almost 16000 server ，if i use more goroutine to do this , block happen frequently
i debug my code , i found the reason
in ping.go 406

`

defer wg.Done()
for {
select {
case <-p.done:
fmt.Println("ok")
return
default:
bytes := make([]byte, 512)
conn.SetReadDeadline(time.Now().Add(time.Millisecond * 100))
var n, ttl int
var err error
if p.ipv4 {
var cm *ipv4.ControlMessage
n, cm, _, err = conn.IPv4PacketConn().ReadFrom(bytes)
if cm != nil {
ttl = cm.TTL
}
} else {
var cm *ipv6.ControlMessage
n, cm, _, err = conn.IPv6PacketConn().ReadFrom(bytes)
if cm != nil {
ttl = cm.HopLimit
}
}
if err != nil {
if neterr, ok := err.(*net.OpError); ok {
if neterr.Timeout() {
// Read timeout
continue
} else {
close(p.done)
return
}
}
}
fmt.Println(len(recv))
recv <- &packet{bytes: bytes, nbytes: n, ttl: ttl}
}
}

`

the wg.Wait() is blocked by p.recvICMP(conn, recv, &wg)
and in the func recvICMP i foud in the for cycle
recv <- &packet{bytes: bytes, nbytes: n, ttl: ttl}
it will block by send a msg to the channel recv
but the chan recv := make(chan *packet, 5) only 5 size
if i do more goroutine i found the size 5 is not enough, so it will be blocked because the full channel ,
ok in some coincidence time the main goroutine dose not do the comsume func
case r := <-recv,
it is do close(p.done) then do wg.Wait() block to wait recvICMP
but in recvICMP
case <-p.done: fmt.Println("ok") return
this code will not effective because the block send msg to channel recv,so will not do
defer wg.Done()
then they all block like a deadlock
i sorry to my poor english
i don't konw i say my question clear
now i just do this to solve recv := make(chan *packet, 100)
by the way do many goroutine it has some wrong result ,some ip can ping right but pinger.PacketsRecv = 0

[CHTJonas]

I believe this is the same issues at #78 and has been fixed by #85 in 70ede2a.