英文:
Go WaitGroup with goroutine
问题
我想知道为什么我们需要在goroutine中运行wg.Wait()。
// 这个例子按预期工作...
func main() {
var wg sync.WaitGroup
for i:=0; i<5; i++ {
wg.Add(1)
go func() {
defer wg.Done()
}()
time.Sleep(time.Second)
}
go func() {
wg.Wait()
}()
}
但是这个例子永远不会结束等待。
func main() {
var wg sync.WaitGroup
for i:=0; i<5; i++ {
wg.Add(1)
go func() {
defer wg.Done()
}()
time.Sleep(time.Second)
}
wg.Wait()
}
有人能解释一下为什么我需要在另一个goroutine中等待吗？
谢谢！
英文:
I wonder why we need to run the wg.Wait() in goroutine
// This one works as expected...
func main() {
var wg sync.WaitGroup
for i:=0; i<5; i++ {
wg.Add(1)
go func() {
defer wg.Done()
}()
time.Sleep(time.Second)
}
go func() {
wg.Wait()
}()
}
But this one never ends waiting forever
func main() {
var wg sync.WaitGroup
for i:=0; i<5; i++ {
wg.Add(1)
go func() {
defer wg.Done()
}()
time.Sleep(time.Second)
}
wg.Wait()
}
Can anybody explain why I need to wait in another goroutine?
Thanks!
答案1
得分: 1
为什么我们需要在goroutine中运行wg.Wait()？
在你提到的例子中（coop/blob/master/coop.go#L85），在goroutine中运行等待是为了立即返回一个通道，该通道将指示所有其他goroutine何时完成。
以下是要启动的goroutine：
for _, fn := range fns {
go func(f func()) {
f()
wg.Done()
}(fn)
}
它们通过var wg sync.WaitGroup来指示完成。
该WaitGroup设置为等待正确数量的goroutine完成：
wg.Add(len(fns))
等待是在goroutine中完成的，因为它将向全局完成通道发出信号：
go func() {
wg.Wait()
doneSig(ch, true)
}()
但是通道会立即返回。
ch := make(chan bool, 1)
...
return ch
这就是为什么等待是异步完成的原因：你不想在这个函数中等待。你只想要通道。
英文:
> why we need to run the wg.Wait() in goroutine?
In the example you mention (coop/blob/master/coop.go#L85), the wait is in a goroutine in order to return immediately a channel that will indicate when all the other goroutines have completed.
Those are the goroutines to be started:
for _, fn := range fns {
go func(f func()) {
f()
wg.Done()
}(fn)
}
They mention the completion through the var wg sync.WaitGroup.
That WaitGroup is set to wait for the right number of goroutines to finish:
wg.Add(len(fns))
The wait is done in a goroutine because it will in turn signal the global completion to a channel:
go func() {
wg.Wait()
doneSig(ch, true)
}()
But the channel is returned immediately.
ch := make(chan bool, 1)
...
return ch
That is why the Wait is done asynchronously: you don't want to wait in this function. You just want the channel.
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