golang panic when invoke http.Get

error message:

goroutine 11357 [runnable]:
net.runtime_pollWait(0x1737f28, 0x77, 0x4fa90)
	/usr/local/go/src/runtime/netpoll.go:157 +0x60
net.(*pollDesc).Wait(0xc829571bf0, 0x77, 0x0, 0x0)
	/usr/local/go/src/net/fd_poll_runtime.go:73 +0x3a
net.(*pollDesc).WaitWrite(0xc829571bf0, 0x0, 0x0)
	/usr/local/go/src/net/fd_poll_runtime.go:82 +0x36
net.(*netFD).connect(0xc829571b90, 0x0, 0x0, 0x1714f80, 0xc829572f20, 0xece412272, 0x33aa2325, 0x473ea0, 0x0, 0x0)
	/usr/local/go/src/net/fd_unix.go:114 +0x1f6
net.(*netFD).dial(0xc829571b90, 0x1714f38, 0x0, 0x1714f38, 0xc8295755c0, 0xece412272, 0x33aa2325, 0x473ea0, 0x0, 0x0)
	/usr/local/go/src/net/sock_posix.go:137 +0x351
net.socket(0x3050e8, 0x3, 0x2, 0x1, 0x0, 0xc829575500, 0x1714f38, 0x0, 0x1714f38, 0xc8295755c0, ...)
	/usr/local/go/src/net/sock_posix.go:89 +0x411
net.internetSocket(0x3050e8, 0x3, 0x1714f38, 0x0, 0x1714f38, 0xc8295755c0, 0xece412272, 0xc833aa2325, 0x473ea0, 0x1, ...)
	/usr/local/go/src/net/ipsock_posix.go:160 +0x141
net.dialTCP(0x3050e8, 0x3, 0x0, 0xc8295755c0, 0xece412272, 0xc833aa2325, 0x473ea0, 0x2, 0x0, 0x0)
	/usr/local/go/src/net/tcpsock_posix.go:171 +0x11e
net.dialSingle(0xc829580b80, 0x1714ea8, 0xc8295755c0, 0xece412272, 0x33aa2325, 0x473ea0, 0x0, 0x0, 0x0, 0x0)
	/usr/local/go/src/net/dial.go:364 +0x3f5
net.dialSerial.func1(0xece412272, 0x33aa2325, 0x473ea0, 0x0, 0x0, 0x0, 0x0)
	/usr/local/go/src/net/dial.go:336 +0x75
net.dial(0x3050e8, 0x3, 0x1714ea8, 0xc8295755c0, 0xc8232f96e8, 0xece412272, 0x33aa2325, 0x473ea0, 0x0, 0x0, ...)
	/usr/local/go/src/net/fd_unix.go:40 +0x60
net.dialSerial(0xc829580b80, 0xc829572f00, 0x2, 0x2, 0x0, 0x0, 0x0, 0x0, 0x0)
	/usr/local/go/src/net/dial.go:338 +0x760
net.(*Dialer).Dial(0xc8200783c0, 0x3050e8, 0x3, 0xc823166ed0, 0x10, 0x0, 0x0, 0x0, 0x0)
	/usr/local/go/src/net/dial.go:232 +0x50f
net.(*Dialer).Dial-fm(0x3050e8, 0x3, 0xc823166ed0, 0x10, 0x0, 0x0, 0x0, 0x0)
	/usr/local/go/src/net/http/transport.go:38 +0x6e
net/http.(*Transport).dial(0xc820092090, 0x3050e8, 0x3, 0xc823166ed0, 0x10, 0x0, 0x0, 0x0, 0x0)
	/usr/local/go/src/net/http/transport.go:499 +0x79
net/http.(*Transport).dialConn(0xc820092090, 0x0, 0x7fff5fbff92a, 0x4, 0xc823166ed0, 0x10, 0x0, 0x0, 0x0)
	/usr/local/go/src/net/http/transport.go:596 +0x19a9
net/http.(*Transport).getConn.func4(0xc820092090, 0x0, 0x7fff5fbff92a, 0x4, 0xc823166ed0, 0x10, 0xc8232a9560)
	/usr/local/go/src/net/http/transport.go:549 +0x66
created by net/http.(*Transport).getConn
	/usr/local/go/src/net/http/transport.go:551 +0x265

source

package main

import (
	"fmt"
	"io/ioutil"
	"net/http"
	"os"
	"strconv"
	"time"
)

func golanggo(url string, round int, c chan int64) {
	for i := 0; i < round; i++ {
		call(url, c)
	}
}

func call(url string, c chan int64) {
	eslap := int64(0)
	defer func() {
		c <- eslap
		//fmt.Println("put", eslap)
		// if err := recover(); err != nil {
		// 	fmt.Println(err)
		// }
	}()
	now := time.Now()
	resp, err := http.Get(url)
	defer resp.Body.Close()
	if err != nil {
		fmt.Println("err:", err)
		return
	}
	if resp.StatusCode == 200 {
		ioutil.ReadAll(resp.Body)
		//fmt.Println(string(data[:]))
	}
	eslap = time.Now().Sub(now).Nanoseconds()
}

func main() {
	url := os.Args[1]
	size, _ := strconv.Atoi(os.Args[2])
	round, _ := strconv.Atoi(os.Args[3])
	c := make(chan int64)

	for i := 0; i < size; i++ {
		go golanggo(url, round, c)
	}

	var total int64 = 0

	var nanos int64
	for i := 0; i < (size * round); i++ {
		//fmt.Print(i)
		nanos = <-c
		//fmt.Println(i, "get", nanos)
		total += nanos
	}

	fmt.Println(total / 1000000)
}

when exec go run client.go http://www.baidu.com 10000 1, and after a few seconds program crash.
when exec go run client.go http://www.baidu.com 100 1, it's ok.

How much of goroutine will cause this error?

Please help me! Thanks.

resp, err := http.Get(url)
defer resp.Body.Close()
if err != nil {
	fmt.Println("err:", err)
	return
}

If err!= nil, then resp==nil, so crash with nil pointer dereference.
Fix ur code with:

resp, err := http.Get(url)
if err != nil {
	fmt.Println("err:", err)
	return
}
defer resp.Body.Close()

You probably hit os thread limit for single go process due to simultaneous hostname resolving using system (cgo-based) resolving. For using pure-go resolving which does not occupy one system thread per resolve request, try setting GOBEBUG environment variable like this export GODEBUG=netdns=go (see https://golang.org/pkg/net doc, "Name Resolution" section).

The default os thread limit for single Go process is set to 10000: https://golang.org/pkg/runtime/debug/#SetMaxThreads

Also it seems that you're running latest Go runtime which outputs trace of a single goroutine by default; running with GOTRACEBACK=all environment variable set will give you much bigger stacktrace — it's always better to post it in full.