golang 并发实例

go关键字实现并发请求示例：
起Numcpu个进程，并发请求url,输出请求结果。

package main

import (
    "fmt"
    "runtime"
    "sync"
    "net/http"
    "io/ioutil"
)

func httpGet(ip string, ports []string, c chan string,wg *sync.WaitGroup) {
    nums := len(ports)
    client := &http.Client{  // 设置http client连接超时时间
        Timeout: 5 * time.Second,
    }
    for i:=0;i<nums;i++{
        url := fmt.Sprintf("http://%s:%s/status.html", ip, ports[i])
        fmt.Println(url)
        resp, err := client.Get(url)
        if err != nil {
            c <- fmt.Sprintf("%s:%s error", ip, ports[i])
            fmt.Println(fmt.Sprintf("%s:%s error", ip, ports[i]))
            wg.Done() //注意wg.Done的放置，确保每次循环都执行
            continue
        }
        body, err := ioutil.ReadAll(resp.Body)
        if err != nil {
            fmt.Println("can not read body.")
        } else {
            c <- string(body)
            resp.Body.Close()
        }
        wg.Done()
    }
}

func main() {
    var procs int
    runtime.GOMAXPROCS(runtime.NumCPU())
    numcpu := runtime.NumCPU()
    ports := []string{"80","8080","8020","18133",}
    if numcpu>len(ports) {
        procs=len(ports)
    }else {
        procs=numcpu
    }
    wg := sync.WaitGroup{}   //利用sync.WaitGroup确保goroutine在main程序前执行完成
    elment := len(ports)/4
    wg.Add(len(ports))
    c := make(chan string,len(ports))
    var start,end int
    for i := 0; i <procs; i++ {
        if i==procs-1 {
            end=len(ports)
        }else {
            end=start+elment
        }
        fmt.Println(ports[start:end])
        go httpGet("192.168.1.240",ports[start:end], c,&wg)
        start +=elment
    }
    wg.Wait()
    fmt.Println("99999999999")
    nums := len(c)
    fmt.Println(len(c))
    for i := 0; i < nums; i++ {
        fmt.Println(<-c)
    }
    defer close(c)
    return

}