为什么所有的goroutine都处于休眠状态 – 死锁。识别瓶颈。

huangapple
go评论104阅读模式
英文:

Why all goroutines are asleep - deadlock. Identifying bottleneck

问题

  1. package main
  3. import (
  4. 	"fmt"
  5. 	"runtime"
  6. 	"sync"
  7. 	"time"
  8. )
  10. func main() {
  11. 	intInputChan := make(chan int, 50)
  12. 	var wg sync.WaitGroup
  13. 	for i := 0; i < 3; i++ {
  14. 		wg.Add(1)
  15. 		go worker(intInputChan, wg)
  16. 	}
  17. 	for i := 1; i < 51; i++ {
  18. 		fmt.Printf("输入：%d \n", i)
  19. 		intInputChan <- i
  20. 	}
  21. 	close(intInputChan)
  22. 	wg.Wait()
  23. 	fmt.Println("主应用程序退出...")
  24. 	panic("---------------")
  25. }
  27. func worker(input chan int, wg sync.WaitGroup) {
  28. 	defer func() {
  29. 		fmt.Println("执行延迟函数...")
  30. 		wg.Done()
  31. 	}()
  33. 	for {
  34. 		select {
  35. 		case intVal, ok := <-input:
  36. 			time.Sleep(100 * time.Millisecond)
  37. 			if !ok {
  38. 				input = nil
  39. 				return
  40. 			}
  41. 			fmt.Printf("%d  %v\n", intVal, ok)
  43. 		default:
  44. 			runtime.Gosched()
  45. 		}
  46. 	}
  47. }

抛出的错误是：

致命错误：所有的goroutine都处于休眠状态 - 死锁！

goroutine 1 [semacquire]:
sync.(*WaitGroup).Wait(0xc082004600)
c:/go/src/sync/waitgroup.go:132 +0x170
main.main()
E:/Go/go_projects/go/src/Test.go:22 +0x21a

英文: 
  1. package main
  3. import (
  4. 	&quot;fmt&quot;
  5. 	&quot;runtime&quot;
  6. 	&quot;sync&quot;
  7. 	&quot;time&quot;
  8. )
  10. func main() {
  11. 	intInputChan := make(chan int, 50)
  12. 	var wg sync.WaitGroup
  13. 	for i := 0; i &lt; 3; i++ {
  14. 		wg.Add(1)
  15. 		go worker(intInputChan, wg)
  16. 	}
  17. 	for i := 1; i &lt; 51; i++ {
  18. 		fmt.Printf(&quot;Inputs. %d \n&quot;, i)
  19. 		intInputChan &lt;- i
  20. 	}
  21. 	close(intInputChan)
  22. 	wg.Wait()
  23. 	fmt.Println(&quot;Existing Main App... &quot;)
  24. 	panic(&quot;---------------&quot;)
  25. }
  27. func worker(input chan int, wg sync.WaitGroup) {
  28. 	defer func() {
  29. 		fmt.Println(&quot;Executing defer..&quot;)
  30. 		wg.Done()
  31. 	}()
  33. 	for {
  34. 		select {
  35. 		case intVal, ok := &lt;-input:
  36. 			time.Sleep(100 * time.Millisecond)
  37. 			if !ok {
  38. 				input = nil
  39. 				return
  40. 			}
  41. 			fmt.Printf(&quot;%d  %v\n&quot;, intVal, ok)
  43. 		default:
  44. 			runtime.Gosched()
  45. 		}
  46. 	}
  48. }

error thrown is.

fatal error: all goroutines are asleep - deadlock!

goroutine 1 [semacquire]:
sync.(*WaitGroup).Wait(0xc082004600)
c:/go/src/sync/waitgroup.go:132 +0x170
main.main()
E:/Go/go_projects/go/src/Test.go:22 +0x21a

答案1

得分: 8

我刚刚尝试了一下（playground），传递了一个wg *sync.WaitGroup，它可以工作。

传递sync.WaitGroup意味着传递了sync.WaitGroup的副本（按值传递）：goroutine将Done()方法应用于不同的sync.WaitGroup。

  1. var wg sync.WaitGroup
  2. for i := 0; i < 3; i++ {
  3. 	wg.Add(1)
  4. 	go worker(intInputChan, &wg)
  5. }

注意&wg：你通过值传递了指向原始sync.WaitGroup的指针，供goroutine使用。

英文:

I just tried it (playground) passing a wg *sync.WaitGroup and it works.

Passing sync.WaitGroup means passing a copy of the sync.WaitGroup (passing by value): the goroutine mentions Done() to a different sync.WaitGroup.

  1. var wg sync.WaitGroup
  2. for i := 0; i &lt; 3; i++ {
  3. 	wg.Add(1)
  4. 	go worker(intInputChan, &amp;wg)
  5. }

Note the &amp;wg: you are passing by value the pointer to the original sync.WaitGroup, for the goroutine to use.

答案2

得分: 3

如上所述，在sync包文档的开头附近提到，不要通过值传递来传递sync包中的类型："不应该复制包含此包中定义的类型的值"，这也包括类型本身（sync.Mutex，sync.WaitGroup等）。

然而，有几点需要注意：

  • 如果你知道要添加多少个，可以只调用一次wg.Add（但要确保在任何地方调用Wait之前完成）。
  • 你不应该像那样调用runtime.Gosched，它会使工作线程忙于循环。
  • 你可以使用range从通道中读取以简化在通道关闭时停止。
  • 对于小函数，你可以使用闭包而不必传递通道或等待组。

代码如下：

  1. package main
  3. import (
  4. 	"fmt"
  5. 	"sync"
  6. 	"time"
  7. )
  9. func main() {
  10. 	const numWorkers = 3
  12. 	c := make(chan int, 10)
  13. 	var wg sync.WaitGroup
  15. 	wg.Add(numWorkers)
  16. 	for i := 0; i < numWorkers; i++ {
  17. 		go func() {
  18. 			defer func() {
  19. 				fmt.Println("执行延迟操作...")
  20. 				wg.Done()
  21. 			}()
  23. 			for v := range c {
  24. 				fmt.Println("接收:", v)
  25. 				time.Sleep(100 * time.Millisecond)
  26. 			}
  27. 		}()
  28. 	}
  30. 	for i := 1; i < 51; i++ {
  31. 		fmt.Println("发送:", i)
  32. 		c <- i
  33. 	}
  34. 	fmt.Println("关闭通道...")
  35. 	close(c)
  37. 	fmt.Println("等待...")
  38. 	wg.Wait()
  39. 	fmt.Println("退出主应用程序...")
  40. }

点击此处查看示例

英文:

As mentioned, don't pass types from the sync package around by value, right near the top of the sync package documentation: "Values containing the types defined in this package should not be copied." That also includes the types themselves (sync.Mutex, sync.WaitGroup, etc).

However, several notes:

  • You can use just a single call to wg.Add if you know how many you're going to add (but as documented make sure it's done before anything can call Wait).
  • You don't want to call runtime.Gosched like that; it makes the workers busy loop.
  • You can use range to read from the channel to simplify stopping when it's closed.
  • For small functions you can use a closure and not bother to pass the channel or wait group at all.

That turns it into this:

  1. package main
  3. import (
  4. 	&quot;fmt&quot;
  5. 	&quot;sync&quot;
  6. 	&quot;time&quot;
  7. )
  9. func main() {
  10. 	const numWorkers = 3
  12. 	c := make(chan int, 10)
  13. 	var wg sync.WaitGroup
  15. 	wg.Add(numWorkers)
  16. 	for i := 0; i &lt; numWorkers; i++ {
  17. 		go func() {
  18. 			defer func() {
  19. 				fmt.Println(&quot;Executing defer…&quot;)
  20. 				wg.Done()
  21. 			}()
  23. 			for v := range c {
  24. 				fmt.Println(&quot;recv:&quot;, v)
  25. 				time.Sleep(100 * time.Millisecond)
  26. 			}
  27. 		}()
  28. 	}
  30. 	for i := 1; i &lt; 51; i++ {
  31. 		fmt.Println(&quot;send:&quot;, i)
  32. 		c &lt;- i
  33. 	}
  34. 	fmt.Println(&quot;closing…&quot;)
  35. 	close(c)
  37. 	fmt.Println(&quot;waiting…&quot;)
  38. 	wg.Wait()
  39. 	fmt.Println(&quot;Exiting Main App... &quot;)
  40. }

<kbd>playground</kbd>

huangapple
  • 本文由 发表于 2015年2月24日 16:23:53
  • 转载请务必保留本文链接：https://go.coder-hub.com/28691035.html
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