Go协程和通道不并行运行

huangapple
go评论120阅读模式
英文:

Go-routines with channels not running parallely

问题

  1. package main
  2. import "time"
  4. func main() {
  5.     stringCh := make(chan func() string)
  6.     go func() {
  7.         stringCh <- func() string {
  8.             return stringReturner()
  9.         }
  10.         close(stringCh)
  11.     }()
  13.     intCh := make(chan func() int)
  14.     go func() {
  15.         intCh <- func() int {
  16.             return intReturner()
  17.         }
  18.         close(intCh)
  19.     }()
  21.     str := (<-stringCh)()
  22.     print("Printing str: ", str,"\n\n")
  23.     num := (<-intCh)()
  24.     print("Printing int: ", num,"\n\n")        
  25. }
  27. func intReturner() int {
  28.     time.Sleep(5 * time.Second)
  29.     print("Inside int returner\n\n")
  30.     return 1
  31. }
  33. func stringReturner() string {
  34.     time.Sleep(5 * time.Second)
  35.     print("Inside string returner\n\n")
  36.     return "abcd"
  37. }

输出：

Inside string returner

Printing str: abcd

等待5秒

Inside int returner

Printing int: 1

https://play.golang.org/p/oE2ybs7Jo-W

为什么这段代码执行需要10秒而不是5秒？我们通过同时启动两个goroutine（一个用于stringReturner，一个用于intReturner）来并行调用，但为什么intReturner在stringReturner执行之后执行？

英文: 
  1. package main
  2. import &quot;time&quot;
  3. func main() {
  4. 	stringCh := make(chan func() (string))
  5. 	go func() {
  6. 		stringCh &lt;- func() (string) {
  7. 			return stringReturner()
  8. 		}
  9. 		close(stringCh)
  10. 	}()
  12. 	intCh := make(chan func() (int))
  13. 	go func() {
  14. 		intCh &lt;- func() (int) {
  15. 			return intReturner()
  16. 		}
  17. 		close(intCh)
  18. 	}()
  20. 	str := (&lt;-stringCh)()
  21. 	print(&quot;Printing str: &quot;, str,&quot;\n\n&quot;)
  22. 	num := (&lt;-intCh)()
  23. 	print(&quot;Printing int: &quot;, num,&quot;\n\n&quot;)		
  24. }
  26. func intReturner()int{
  27. 	time.Sleep(5 * time.Second)
  28. 	print(&quot;Inside int returner\n\n&quot;);
  29. 	return 1;
  30. }
  32. func stringReturner()string{
  33. 	time.Sleep(5 * time.Second)
  34. 	print(&quot;Inside string returner\n\n&quot;);
  35. 	return &quot;abcd&quot;;
  36. }

Output:

Inside string returner

Printing str: abcd

WAIT OF 5 SECONDS

Inside int returner

Printing int: 1

https://play.golang.org/p/oE2ybs7Jo-W

Why is this coding taking 10 seconds to execute instead of 5? We are parallelizing the calls by spawning two go-routines right (1 for string returner and 1 for int returner), but why is the int returner executing after the string returner executes?

答案1

得分: 3

该通道返回一个带有延时的函数，并且这个函数按顺序调用。这就是为什么通常需要10秒的原因。

https://play.golang.org/p/UpHD7Ttw03R

英文:

The channel is returning function with sleep, and such function got called in sequential manner. That is why it will take 10s in general.

https://play.golang.org/p/UpHD7Ttw03R

答案2

得分: 1

这是因为你只是并行地向通道写入数据，但是从通道读取数据是按顺序进行的。要解决这个问题，你可以使用单独的goroutine从两个通道读取数据。

  1. var wg sync.WaitGroup
  2. wg.Add(2)
  3. go func() {
  4.   defer wg.Done()
  5.   str := (<-stringCh)()
  6.   print("打印字符串: ", str, "\n\n")
  7. }()
  8. go func() {
  9.   defer wg.Done()
  10.   num := (<-intCh)()
  11.   print("打印整数: ", num, "\n\n")
  12. }()
  13. wg.Wait()
英文:

Thats because you are only writing to the channels parallelly. But the read from the channels are happening one-after-the-other. To fix this, you can read from both channels from separate go routines

  1. var wg sync.WaitGroup
  2. wg.Add(2)
  3. go func() {
  4.   defer wg.Done()
  5.   str := (&lt;-stringCh)()
  6.   print(&quot;Printing str: &quot;, str, &quot;\n\n&quot;)
  7. }()
  8. go func() {
  9.   defer wg.Done()
  10.   num := (&lt;-intCh)()
  11.   print(&quot;Printing int: &quot;, num, &quot;\n\n&quot;)
  12. }()
  13. wg.Wait()

答案3

得分: 1

根据建议，将sleep方法移入go routine以在5秒内同时运行两个函数：

  1. package main
  3. import "time"
  5. func main() {
  6.     stringCh := make(chan func() string)
  7.     go func() {
  8.         time.Sleep(5 * time.Second)
  9.         stringCh <- func() string {
  10.             return stringReturner()
  11.         }
  12.         close(stringCh)
  13.     }()
  15.     intCh := make(chan func() int)
  16.     go func() {
  17.         time.Sleep(5 * time.Second)
  18.         intCh <- func() int {
  19.             return intReturner()
  20.         }
  21.         close(intCh)
  22.     }()
  24.     str := (<-stringCh)()
  25.     print("Printing str: ", str, "\n\n")
  26.     num := (<-intCh)()
  27.     print("Printing int: ", num, "\n\n")
  28. }
  30. func intReturner() int {
  31.     print("Inside int returner\n\n")
  32.     return 1
  33. }
  35. func stringReturner() string {
  36.     print("Inside string returner\n\n")
  37.     return "abcd"
  38. }

输出：

  1. Inside string returner
  3. Printing str: abcd
  5. Inside int returner
  7. Printing int: 1
英文:

Based on the suggestions moving the sleep method into go routine to run both functions concurrently in 5s:

  1. package main
  3. import &quot;time&quot;
  5. func main() {
  6. 	stringCh := make(chan func() string)
  7. 	go func() {
  8. 		time.Sleep(5 * time.Second)
  9. 		stringCh &lt;- func() string {
  10. 			return stringReturner()
  11. 		}
  12. 		close(stringCh)
  13. 	}()
  15. 	intCh := make(chan func() int)
  16. 	go func() {
  17. 		time.Sleep(5 * time.Second)
  18. 		intCh &lt;- func() int {
  19. 			return intReturner()
  20. 		}
  21. 		close(intCh)
  22. 	}()
  24. 	str := (&lt;-stringCh)()
  25. 	print(&quot;Printing str: &quot;, str, &quot;\n\n&quot;)
  26. 	num := (&lt;-intCh)()
  27. 	print(&quot;Printing int: &quot;, num, &quot;\n\n&quot;)
  28. }
  30. func intReturner() int {
  31. 	print(&quot;Inside int returner\n\n&quot;)
  32. 	return 1
  33. }
  35. func stringReturner() string {
  36. 	print(&quot;Inside string returner\n\n&quot;)
  37. 	return &quot;abcd&quot;
  38. }

Output:

  1. Inside string returner
  3. Printing str: abcd
  5. Inside int returner
  7. Printing int: 1

huangapple
  • 本文由 发表于 2021年6月27日 12:55:28
  • 转载请务必保留本文链接：https://go.coder-hub.com/68148113.html
  • go
  • goroutine
  • parallel-processing
匿名

发表评论

匿名网友

:?: :razz: :sad: :evil: :!: :smile: :oops: :grin: :eek: :shock: :???: :cool: :lol: :mad: :twisted: :roll: :wink: :idea: :arrow: :neutral: :cry: :mrgreen:

确定