golang中协程同步sync.waitGroup

//使用golang中sync.WaitGroup来实现协程同步

package main

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

var waitGroup = new(sync.WaitGroup)
func download(i int ){
url := fmt.Sprintf("http://pic2016.ytqmx.com:82/2016/0919/41/%d.jpg", i)
fmt.Printf("开始下载:%s\n", url)
res,err := http.Get(url)
if err != nil || res.StatusCode != 200{
fmt.Printf("下载失败:%s", res.Request.URL)
}
fmt.Printf("开始读取文件内容,url=%s\n", url)
data ,err2 := ioutil.ReadAll(res.Body)
if err2 != nil {
fmt.Printf("读取数据失败")
}

ioutil.WriteFile(fmt.Sprintf("pic2016/1_%d.jpg", i), data, 0644)
//计数器-1
waitGroup.Done()
}

func main()  {
//创建多个协程，同时下载多个图片
os.MkdirAll("pic2016", 0666)
now := time.Now()

for i :=1; i<24; i++ {
//计数器+1
waitGroup.Add(1)
go download(i)
}

//等待所有协程操作完成
waitGroup.Wait()
fmt.Printf("下载总时间:%v\n", time.Now().Sub(now))
}