英文:
How to use sync.WaitGroup in pipeline
问题
我正在尝试在Go中实现一个流水线，但遇到了一个问题：程序在其他goroutine完成之前就退出了主goroutine。
请使用**等待组（wait groups）**来修复这个问题。
package main
import (
"fmt"
"sync"
)
var wg sync.WaitGroup
func main() {
c1 := make(chan string)
c2 := make(chan string)
go sender(c1)
go removeDuplicates(c1, c2)
go printer(c2)
wg.Wait()
}
func sender(outputStream chan string) {
wg.Add(1)
defer wg.Done()
for _, v := range []string{"one", "one", "two", "two", "three", "three"} {
outputStream <- v
}
close(outputStream)
}
func removeDuplicates(inputStream, outputStream chan string) {
wg.Add(1)
defer wg.Done()
temp := ""
for v := range inputStream {
if v != temp {
outputStream <- v
temp = v
}
}
close(outputStream)
}
func printer(inputStream chan string) {
wg.Add(1)
defer wg.Done()
for v := range inputStream {
fmt.Println(v)
}
}
当我在这种情况下使用time.Sleep时，程序成功运行。
英文:
I'm trying to implement a pipeline in Go and there was a problem that the program exits the main goroutine before the rest of the goroutines are finished.
Please, help fix this case using wait groups.
package main
import (
"fmt"
"sync"
)
var wg sync.WaitGroup
func main() {
c1 := make(chan string)
c2 := make(chan string)
go sender(c1)
go removeDuplicates(c1, c2)
go printer(c2)
wg.Wait()
}
func sender(outputStream chan string) {
wg.Add(1)
wg.Done()
for _, v := range []string{"one", "one", "two", "two", "three", "three"} {
outputStream <- v
}
close(outputStream)
}
func removeDuplicates(inputStream, outputStream chan string) {
wg.Add(1)
wg.Done()
temp := ""
for v := range inputStream {
if v != temp {
outputStream <- v
temp = v
}
}
close(outputStream)
}
func printer(inputStream chan string) {
wg.Add(1)
wg.Done()
for v := range inputStream {
fmt.Println(v)
}
}
When I used time.Sleep in this case, the program worked successfully.
答案1
得分: 2
使用等待组（WaitGroup）的第一条规则是：不要在你要等待的goroutine中调用Add()方法。可能会出现在Add()之前调用Wait()的情况，这不是你期望的结果。第二条规则是：在结束时调用Done()方法，而不是在开始时调用。所以，修复的代码如下：
func main() {
c1 := make(chan string)
c2 := make(chan string)
wg.Add(3)
go sender(c1)
go removeDuplicates(c1, c2)
go printer(c2)
wg.Wait()
}
func sender(outputStream chan string) {
defer wg.Done()
for _, v := range []string{"one", "one", "two", "two", "three", "three"} {
outputStream <- v
}
close(outputStream)
}
// 其他两个函数类似
请注意，这是一个示例代码，其中使用了等待组（WaitGroup）来同步goroutine的执行顺序。
英文:
The first rules of working with wait groups: don't call Add() from a goroutine you're going to wait for. It is possible, that Wait() will be called before Add(), which is not what you expect. The second rule: call Done() in the end, not in the beginning. So, the fix would be:
func main() {
c1 := make(chan string)
c2 := make(chan string)
wg.Add(3)
go sender(c1)
go removeDuplicates(c1, c2)
go printer(c2)
wg.Wait()
}
func sender(outputStream chan string) {
defer wg.Done()
for _, v := range []string{"one", "one", "two", "two", "three", "three"} {
outputStream <- v
}
close(outputStream)
}
// etc for other two functions
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