从接收通道进行阻塞

huangapple
go评论135阅读模式
英文:

Go blocking from receiving channel

问题

我有以下的Go代码来等待流。预期的输出是：

  1. line1
  2. line2
  3. line3
  4. line4
  5. line5
  6. escape1
  7. scan done
  8. done....

但是在line5之后，我的代码一直挂起。

  1. var lines = `
  2. line1
  3. line2
  4. line3
  5. line4
  6. line5
  7. line6
  8. line7
  9. `
  11. func main() {
  12.     var (
  13.         donec  = make(chan struct{})
  14.         stream = make(chan string, 5000)
  15.         exitc  = make(chan struct{})
  16.     )
  17.     go func() {
  18.         scanner := bufio.NewScanner(strings.NewReader(lines))
  19.     escape1:
  20.         for {
  21.             for scanner.Scan() {
  22.                 select {
  23.                 case <-donec:
  24.                     fmt.Println("escape1")
  25.                     close(stream)
  26.                     break escape1
  27.                 default:
  28.                     stream <- scanner.Text()
  29.                 }
  30.             }
  31.         }
  32.         close(exitc)
  33.         fmt.Println("scan done")
  34.         return
  35.     }()
  37. escape2:
  38.     for {
  39.         select {
  40.         case txt, ok := <-stream:
  41.             if !ok {
  42.                 fmt.Println("stream closed!")
  43.             }
  44.             fmt.Println(txt)
  45.             if strings.Contains(txt, "line5") {
  46.                 close(donec)
  47.                 <-exitc
  48.                 break escape2
  49.             }
  50.         }
  51.     }
  52.     fmt.Println("done....")
  53. }

我认为我做得没错。有人可以帮我调试这个挂起的代码吗？

谢谢！

英文:

I have the following go code to wait for streams. The expected output is:

  1. line1
  2. line2
  3. line3
  4. line4
  5. line5
  6. escape1
  7. scan done
  8. done....

But after line5, my code keeps hanging.

  1. var lines = `
  2. line1
  3. line2
  4. line3
  5. line4
  6. line5
  7. line6
  8. line7
  9. `
  11. func main() {
  12.     var (
  13.         donec  = make(chan struct{})
  14.         stream = make(chan string, 5000)
  15.         exitc  = make(chan struct{})
  16.     )
  17.     go func() {
  18.         scanner := bufio.NewScanner(strings.NewReader(lines))
  19.     escape1:
  20.         for {
  21.             for scanner.Scan() {
  22.                 select {
  23.                 case &lt;-donec:
  24.                     fmt.Println(&quot;escape1&quot;)
  25.                     close(stream)
  26.                     break escape1
  27.                 default:
  28.                     stream &lt;- scanner.Text()
  29.                 }
  30.             }
  31.         }
  32.         close(exitc)
  33.         fmt.Println(&quot;scan done&quot;)
  34.         return
  35.     }()
  37. escape2:
  38.     for {
  39.         select {
  40.         case txt, ok := &lt;-stream:
  41.             if !ok {
  42.                 fmt.Println(&quot;stream closed!&quot;)
  43.             }
  44.             fmt.Println(txt)
  45.             if strings.Contains(txt, &quot;line5&quot;) {
  46.                 close(donec)
  47.                 &lt;-exitc
  48.                 break escape2
  49.             }
  50.         }
  51.     }
  52.     fmt.Println(&quot;done....&quot;)
  53. }

Think I am doing everything right. Could anybody help me debug this hanging code?

Thanks!

答案1

得分: 1

我认为问题出在你的 escape1 循环包裹了 for scanner.Scan() 循环。

当我移除外部的循环后，代码在我这里可以正常工作：https://play.golang.org/p/NU3m3Deil7

  1. func main() {
  2.     var (
  3.         donec  = make(chan struct{})
  4.         stream = make(chan string, 5000)
  5.         exitc  = make(chan struct{})
  6.     )
  7.     go func() {
  8.         scanner := bufio.NewScanner(strings.NewReader(lines))
  9.     escape1:
  10.         for scanner.Scan() {
  11.             select {
  12.             case <-donec:
  13.                 fmt.Println("escape1")
  14.                 close(stream)
  15.                 break escape1
  16.             default:
  17.                 stream <- scanner.Text()
  18.             }
  19.         }
  21.         close(exitc)
  22.         fmt.Println("scan done")
  23.         return
  24.     }()
  26. escape2:
  27.     for {
  28.         select {
  29.         case txt, ok := <-stream:
  30.             if !ok {
  31.                 fmt.Println("stream closed!")
  32.             }
  33.             fmt.Println(txt)
  34.             if strings.Contains(txt, "line5") {
  35.                 close(donec)
  36.                 <-exitc
  37.                 break escape2
  38.             }
  39.         }
  40.     }
  41.     fmt.Println("done....")
  42. }

请注意，我只是翻译了你的代码，并没有回答你的问题。

英文:

I think it's because your escape1 for loop wraps the for scanner.Scan() loop.

When I remove that outer for loop it works fine for me: https://play.golang.org/p/NU3m3Deil7

  1. func main() {
  2. 	var (
  3. 		donec  = make(chan struct{})
  4. 		stream = make(chan string, 5000)
  5. 		exitc  = make(chan struct{})
  6. 	)
  7. 	go func() {
  8. 		scanner := bufio.NewScanner(strings.NewReader(lines))
  9. 	escape1:
  10. 		for scanner.Scan() {
  11. 			select {
  12. 			case &lt;-donec:
  13. 				fmt.Println(&quot;escape1&quot;)
  14. 				close(stream)
  15. 				break escape1
  16. 			default:
  17. 				stream &lt;- scanner.Text()
  18. 			}
  19. 		}
  21. 		close(exitc)
  22. 		fmt.Println(&quot;scan done&quot;)
  23. 		return
  24. 	}()
  26. escape2:
  27. 	for {
  28. 		select {
  29. 		case txt, ok := &lt;-stream:
  30. 			if !ok {
  31. 				fmt.Println(&quot;stream closed!&quot;)
  32. 			}
  33. 			fmt.Println(txt)
  34. 			if strings.Contains(txt, &quot;line5&quot;) {
  35. 				close(donec)
  36. 				&lt;-exitc
  37. 				break escape2
  38. 			}
  39. 		}
  40. 	}
  41. 	fmt.Println(&quot;done....&quot;)
  42. }

huangapple
  • 本文由 发表于 2016年3月29日 07:03:35
  • 转载请务必保留本文链接：https://go.coder-hub.com/36272673.html
  • channel
  • concurrency
  • go
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