sync.WaitGroup不等待 [英] sync.WaitGroup doesnt waits

问题描述

可能是我看不到明显的东西，我在做什么错了：

May be I can not see obvious thing, what am I doing wrong:

func printSize (listOfUrls []string){
    var wg sync.WaitGroup
    wg.Add(len(listOfUrl))
    for _, myurl := range(listOfUrls){
        go func(){
               body := getUrlBody(myurl)
               fmt.Println(len(body))
               wg.Done()
           }()    
    } 
    wg.Wait()
}

如果我删除wg并走了，我会收到每个网址正文的大小正确地。如果我像上面那样做，它几乎立即打印零。 getUrlBody（）有时要花几分钟才能执行。

If I remove wg and go, I receive the size of each url body correctly. If I do it as in above, it prints zeroes almost instantly. The getUrlBody() takes time to execute sometimes minutes.

答案：我也尝试过这种方法，可以肯定的是，它也表现出相同的行为。
我发现错误在于getUrlBody和main（）函数...

Answering comment: I also tried it this way, to be sure, and it demonstrate same behaviour. I found the error was in getUrlBody and main() function...

func printSize(listOfUrls []string) {
    var wg sync.WaitGroup
    wg.Add(len(listOfUrls))
        for _, myurl := range listOfUrls {
          go f(myurl, &wg)
        }
    wg.Wait()
}

func f(myurl string, wg *sync.WaitGroup) {
    body := getUrlBody(myurl)
    fmt.Println(len(body))
    wg.Done()
 }

推荐答案

所有goroutine都共享单个 myurl 变量。有关更多信息，请参见 https://golang.org/doc/faq#closures_and_goroutines 。

All of the goroutines are sharing the single myurl variable. See https://golang.org/doc/faq#closures_and_goroutines for more information.

将代码更改为：

func f(listOfUrls []string){
  var wg sync.WaitGroup
  wg.Add(len(listOfUrl))
  for _, myurl := range(listOfUrls){
    go func(myurl string){
           body := getUrlBody(myurl)
           fmt.Println(len(body))
           wg.Done()
       }(myurl)    
  } 
  wg.Wait()
}

或

func f(listOfUrls []string){
  var wg sync.WaitGroup
  wg.Add(len(listOfUrl))
  for _, myurl := range(listOfUrls){
    myurl := myurl
    go func(){
           body := getUrlBody(myurl)
           fmt.Println(len(body))
           wg.Done()
       }()    
  } 
  wg.Wait()
}

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