WaitGroup 会将main goroutine阻塞直到所有的goroutine运行结束,从而达到并发控制的目的。使用方法非常简单,真心佩服创造Golang的大师们!

type WaitGroup               //相当于一个箱子,将main goroutine 保护到里面

func (*WaitGroup) Add   //调用一次为箱子加一把锁(当然,你愿意也可以多把)

func (*WaitGroup) Done  // 调用一次开一把锁(only one!)

func (*WaitGroup) Wait    //箱子的盖子,没锁了自动打开

官网说明:一个WaitGroup锁等待一个goroutines合集结束。main goroutine里面调用Add方法设置需要等待的goroutines 数量,然后运行每一个goroutine,并且当其结束时调用Done方法。同时,main goroutine 被锁住直到所有的goroutines完成。

使用方法(官网Example):

var wg sync.WaitGroup
var urls = []string{
"http://www.golang.org/",
"http://www.google.com/",
"http://www.somestupidname.com/",
}
for _, url := range urls {
  // Increment the WaitGroup counter.
  wg.Add()
  // Launch a goroutine to fetch the URL.
  go func(url string) {
    // Decrement the counter when the goroutine completes.
    defer wg.Done()
    // Fetch the URL.
    http.Get(url)
  }(url)
}
// Wait for all HTTP fetches to complete.
wg.Wait()

任何放在wg.Wait() 后面的语句阻塞,直到所有的goroutine返回:

package main

import (
"fmt"
"net/http"
"sync"
) func main() {
var wg sync.WaitGroup
var urls = []string{
"http://www.golang.org/",
"http://www.google.com/",
"http://www.somestupidname.com/",
}
for _, url := range urls {
// Increment the WaitGroup counter.
wg.Add()
// Launch a goroutine to fetch the URL.
go func(url string) {
// Decrement the counter when the goroutine completes.
defer wg.Done()
// Fetch the URL.
http.Get(url)
fmt.Println("我先干活, 主程序等着我")
}(url)
}
// Wait for all HTTP fetches to complete.
wg.Wait()
fmt.Println("应该最后才出来") }
05-11 09:43