英文:
A Tour of Go example on Goroutines concurrency
问题
我是你的中文翻译助手，以下是翻译好的内容：
我对Go语言还不熟悉，在这里学习：https://tour.golang.org/concurrency/1
当我运行https://play.golang.org/p/9JvbtSuv5o时，结果是：
world
hello
hello
所以我添加了sync.WaitGroup：https://play.golang.org/p/vjdhnDssGk
package main
import (
"fmt"
"sync"
"time"
)
var w sync.WaitGroup
func say(s string) {
for i := 0; i < 2; i++ {
time.Sleep(100 * time.Millisecond)
fmt.Println(s)
}
w.Done()
}
func main() {
w.Add(1)
go say("world")
say("hello")
w.Wait()
}
但结果仍然相同：
world
hello
hello
我的代码有什么问题？
请帮忙看看，谢谢你的帮助。
英文:
I'm new to the Go Language, and learning here:
https://tour.golang.org/concurrency/1
When I run https://play.golang.org/p/9JvbtSuv5o the result is:
world
hello
hello
So Added sync.WaitGroup: https://play.golang.org/p/vjdhnDssGk
<!-- language: lang-golang -->
package main
import (
"fmt"
"sync"
"time"
)
var w sync.WaitGroup
func say(s string) {
for i := 0; i < 2; i++ {
time.Sleep(100 * time.Millisecond)
fmt.Println(s)
}
w.Done()
}
func main() {
w.Add(1)
go say("world")
say("hello")
w.Wait()
}
But the result is same:
world
hello
hello
What is wrong with my code?
Please help,
Thank you for your help.
答案1
得分: 0
w.Done() 函数会减少 WaitGroup 计数器的值。所以你的代码有时会出现 panic: sync: negative WaitGroup counter 的错误。
你有两个 Goroutine：
1 - go say("world")
2 - say("hello") 在 main Goroutine 中
所以使用 w.Add(2)，可以参考这个工作示例（The Go Playground）：
package main
import (
"fmt"
"sync"
"time"
)
var w sync.WaitGroup
func say(s string) {
for i := 0; i < 2; i++ {
time.Sleep(100 * time.Millisecond)
fmt.Println(s)
}
w.Done()
}
func main() {
w.Add(2)
go say("world")
say("hello")
w.Wait()
}
输出结果：
world
hello
hello
world
希望对你有所帮助。
英文:
w.Done() decrements the WaitGroup counter.
So your code even sometimes panic: sync: negative WaitGroup counter.
You have two Goroutines:
1 - go say("world")
2 - say("hello") inside main Goroutine
so use w.Add(2), see this working sample (The Go Playground):
<!-- language: lang-golang -->
package main
import (
"fmt"
"sync"
"time"
)
var w sync.WaitGroup
func say(s string) {
for i := 0; i < 2; i++ {
time.Sleep(100 * time.Millisecond)
fmt.Println(s)
}
w.Done()
}
func main() {
w.Add(2)
go say("world")
say("hello")
w.Wait()
}
output:
world
hello
hello
world
I hope this helps.
答案2
得分: 0
你只是将WaitGroup增加了1，但是从两个say的调用中调用了Done。
在你的示例中，如果将WaitGroup的初始值设为2，就可以正常工作。
w.Add(2)
英文:
You're only adding 1 to the WaitGroup, but calling Done from 2 invocations of say.
In your example, starting the WaitGroup with 2 would work
w.Add(2)
答案3
得分: 0
问题是由于对w.Done()的无条件调用而引起的。所以当你调用say("hello")时，这也会减少waitGroup的计数器。
请参考 https://play.golang.org/p/wJeAyYyjA2
package main
import (
"fmt"
"sync"
"time"
)
var w sync.WaitGroup
func say(s string, async bool) {
if async {
defer w.Done()
}
for i := 0; i < 2; i++ {
time.Sleep(100 * time.Millisecond)
fmt.Println(s)
}
}
func main() {
w.Add(1)
go say("world", true)
say("hello", false)
w.Wait()
}
英文:
Problem occurs due to unconditional call to w.Done(). So when u called say("hello") this also decremented counter for waitGroup.
Refer https://play.golang.org/p/wJeAyYyjA2
package main
import (
"fmt"
"sync"
"time"
)
var w sync.WaitGroup
func say(s string, async bool) {
if async {
defer w.Done()
}
for i := 0; i < 2; i++ {
time.Sleep(100 * time.Millisecond)
fmt.Println(s)
}
}
func main() {
w.Add(1)
go say("world", true)
say("hello", false)
w.Wait()
}
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