如题，最近在写一个高并发查询大量域名A记录的工具，使用的是github.com/miekg/dns这个包，基本思路是给定一个域名列表和dns服务器列表，将dns服务器做成循环链表，将dns服务器与域名一一对应存入map然后交给worker解析，当域名大约在10万以上的，goroutine在2000左右就会出现大量占用cpu的情况。请问各位有没有写过类似程序的经验，请教一下应该是哪里出问题了。代码如下。用pprof查看显示是 lookup占用了大量cpu。也测试过和并发map应该没关系。
```
package main
import (
"bufio"
"container/ring"
"errors"
"fmt"
"github.com/miekg/dns"
cmap "github.com/orcaman/concurrent-map"
"log"
"os"
"time"
)
var (
client = new(dns.Client)
)
var (
signalsnum = 0
)
func init() {
client.Timeout = time.Duration(500*time.Millisecond)
}
func lookupA(fqdn, serverAddr string) ([]string, error) {
var ips []string
m1 := new(dns.Msg)
m1.Id = dns.Id()
m1.RecursionDesired = true
m1.Question = make([]dns.Question, 1)
m1.Question[0] = dns.Question{dns.Fqdn(fqdn), dns.TypeA, dns.ClassINET}
in, _, err := client.Exchange(m1, serverAddr+":53")
if err != nil {
return ips,err
}
if len(in.Answer) < 1 {
return ips, errors.New("no answer")
}
for _, answer := range in.Answer {
if a, ok := answer.(*dns.A); ok {
ips = append(ips, a.A.String())
return ips,nil
}
}
return ips, nil
}
func worker(dnsmapkey chan string,gather chan string,m cmap.ConcurrentMap) {
for {
select {
case name := <-dnsmapkey:
dnskey, _ := m.Get(name)
dnserver := fmt.Sprintf("%s", dnskey)
//fmt.Println(name,"========",dnserver)
result, err := lookupA(name+".lenovo.com", dnserver)
if err != nil {
//有err就认为解析失败，加入失败队列。
}
if len(result) > 0 {
signalsnum++
gather <- name + "===" + result[0] + "===" + dnserver
}
m.Remove(name)
}
}
}
func filelines(name string) int {
line := 0
file,err := os.Open(name)
if err != nil{
log.Fatal(err)
}
defer file.Close()
scanner := bufio.NewScanner(file)
for scanner.Scan(){
line++
}
return line
}
var (
hashMapSize = 3000
)
func main() {
//profile.Start().Stop()
r := ring.New(filelines("../dns.txt"))
//var results []string
dnsmapkey := make(chan string, hashMapSize)
m := cmap.New()
gather := make(chan string)
fh, err := os.Open("./hostname.txt")
if err != nil {
panic(err)
}
defer fh.Close()
dnsfile, err := os.Open("../dns.txt")
if err != nil {
panic(err)
}
defer dnsfile.Close()
namescanner := bufio.NewScanner(fh)
dnscanner := bufio.NewScanner(dnsfile)
for dnscanner.Scan(){
r.Value = dnscanner.Text()
r = r.Next()
}
for i := 0; i < hashMapSize; i++ {
go worker(dnsmapkey,gather,m)
}
for namescanner.Scan() {
name := namescanner.Text()
dns := fmt.Sprintf("%s",r.Value)
m.Set(name,dns)
dnsmapkey <- name
r = r.Next()
}
close(dnsmapkey)
for i:=0;i<signalsnum;i++{
fmt.Println(<-gather)
}
}
```
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