[英]sync.WaitGroup doesnt waits
May be I can not see obvious thing, what am I doing wrong: 可能是我看不到明显的东西,我在做什么错:
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()
}
If I remove wg and go, I receive the size of each url body correctly. 如果删除wg并走,我将正确接收每个URL主体的大小。 If I do it as in above, it prints zeroes almost instantly. 如果我按照上面的方法进行操作,它将几乎立即输出零。 The getUrlBody() takes time to execute sometimes minutes. getUrlBody()有时需要花费几分钟才能执行。
Answering comment: I also tried it this way, to be sure, and it demonstrate same behaviour. 回答评论:可以肯定的是,我也尝试过这种方法,并且表现出相同的行为。 I found the error was in getUrlBody and main() function... 我发现错误发生在getUrlBody和main()函数中...
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()
}
All of the goroutines are sharing the single myurl
variable. 所有goroutine都共享一个myurl
变量。 See https://golang.org/doc/faq#closures_and_goroutines for more information. 有关更多信息,请参见https://golang.org/doc/faq#closures_and_goroutines 。
Change the code to: 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()
}
or 要么
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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