在 Goroutine 中等待管道 io.Copy 时发生死锁。

huangapple
go评论112阅读模式
英文:

Deadlock while waiting for piped io.Copy in Goroutine

问题

在下面的代码中，对io.Copy的调用永远不会返回；它只会无限期地阻塞，导致死锁。只有在使用io.Pipe将read的io.Reader连接到os.Stdout的io.Writer时才会出现这种行为。然而，我需要使用管道，因为在我的完整代码中，我正在使用io.MultiWriter和io.Pipe将一个io.Reader连接到多个期望io.Reader的函数。

以下是代码：

  1. func main() {
  2. 	read := strings.NewReader("abcdefghij")
  3. 	pipeReader, pipeWriter := io.Pipe()
  5. 	var wg sync.WaitGroup
  6. 	wg.Add(1)
  7. 	go func() {
  8. 		println("Start copy")
  9. 		_, err := io.Copy(os.Stdout, pipeReader)
  10. 		if err != nil {
  11. 			println(err.Error())
  12. 		}
  13. 		println("End copy")
  14. 		wg.Done()
  15. 	}()
  17. 	_, err := io.Copy(pipeWriter, read)
  18. 	if err != nil {
  19. 		println(err.Error())
  20. 	}
  22. 	wg.Wait()
  23. }

输出：

  1. Start copy
  2. abcdefghij
  3. fatal error: all goroutines are asleep - deadlock!
  5. goroutine 1 [semacquire]:
  6. sync.runtime_Semacquire(0xc0000b0018?)
  7. 	/usr/local/go-faketime/src/runtime/sema.go:62 +0x25
  8. sync.(*WaitGroup).Wait(0x4969c8?)
  9. 	/usr/local/go-faketime/src/sync/waitgroup.go:139 +0x52
  10. main.main()
  11. 	/tmp/sandbox4108076976/prog.go:31 +0x23c
  13. goroutine 18 [select]:
  14. io.(*pipe).read(0xc0000a6120, {0xc0000b6000, 0x8000, 0xc00009e101?})
  15. 	/usr/local/go-faketime/src/io/pipe.go:57 +0xb1
  16. io.(*PipeReader).Read(0x10?, {0xc0000b6000?, 0xc00009e1e0?, 0x4f75a0?})
  17. 	/usr/local/go-faketime/src/io/pipe.go:136 +0x25
  18. io.copyBuffer({0x496aa8, 0xc00009e1e0}, {0x4969a8, 0xc0000a4018}, {0x0, 0x0, 0x0})
  19. 	/usr/local/go-faketime/src/io/io.go:427 +0x1b2
  20. io.Copy(...)
  21. 	/usr/local/go-faketime/src/io/io.go:386
  22. os.genericReadFrom(0xb000000006018ab?, {0x4969a8, 0xc0000a4018})
  23. 	/usr/local/go-faketime/src/os/file.go:162 +0x67
  24. os.(*File).ReadFrom(0xc0000a4008, {0x4969a8, 0xc0000a4018})
  25. 	/usr/local/go-faketime/src/os/file.go:156 +0x1b0
  26. io.copyBuffer({0x496a28, 0xc0000a4008}, {0x4969a8, 0xc0000a4018}, {0x0, 0x0, 0x0})
  27. 	/usr/local/go-faketime/src/io/io.go:413 +0x14b
  28. io.Copy(...)
  29. 	/usr/local/go-faketime/src/io/io.go:386
  30. main.main.func1()
  31. 	/tmp/sandbox4108076976/prog.go:18 +0x71
  32. created by main.main
  33. 	/tmp/sandbox4108076976/prog.go:16 +0x1d3

这是代码的 playground 链接：https://goplay.tools/snippet/70UbGIz8fTV

有没有办法在保持io.Pipe的情况下避免死锁呢？

英文:

In the code below, the call to io.Copy never returns; it just blocks indefinitely, causing a deadlock. This behaviour only occurs when the io.Pipe is used to connect the read io.Reader to the os.Stdout io.Writer. However, I need to use the pipe since, in my full code, I am using io.MultiWriter with io.Pipes to connect one io.Reader to many functions expecting an io.Reader.

  1. func main() {
  2. 	read := strings.NewReader("abcdefghij")
  3. 	pipeReader, pipeWriter := io.Pipe()
  5. 	var wg sync.WaitGroup
  6. 	wg.Add(1)
  7. 	go func() {
  8. 		println("Start copy")
  9. 		_, err := io.Copy(os.Stdout, pipeReader)
  10. 		if err != nil {
  11. 			println(err.Error())
  12. 		}
  13. 		println("End copy")
  14. 		wg.Done()
  15. 	}()
  17. 	_, err := io.Copy(pipeWriter, read)
  18. 	if err != nil {
  19. 		println(err.Error())
  20. 	}
  22. 	wg.Wait()
  23. }

Output:

  1. Start copy
  2. abcdefghij
  3. fatal error: all goroutines are asleep - deadlock!
  5. goroutine 1 [semacquire]:
  6. sync.runtime_Semacquire(0xc0000b0018?)
  7. 	/usr/local/go-faketime/src/runtime/sema.go:62 +0x25
  8. sync.(*WaitGroup).Wait(0x4969c8?)
  9. 	/usr/local/go-faketime/src/sync/waitgroup.go:139 +0x52
  10. main.main()
  11. 	/tmp/sandbox4108076976/prog.go:31 +0x23c
  13. goroutine 18 [select]:
  14. io.(*pipe).read(0xc0000a6120, {0xc0000b6000, 0x8000, 0xc00009e101?})
  15. 	/usr/local/go-faketime/src/io/pipe.go:57 +0xb1
  16. io.(*PipeReader).Read(0x10?, {0xc0000b6000?, 0xc00009e1e0?, 0x4f75a0?})
  17. 	/usr/local/go-faketime/src/io/pipe.go:136 +0x25
  18. io.copyBuffer({0x496aa8, 0xc00009e1e0}, {0x4969a8, 0xc0000a4018}, {0x0, 0x0, 0x0})
  19. 	/usr/local/go-faketime/src/io/io.go:427 +0x1b2
  20. io.Copy(...)
  21. 	/usr/local/go-faketime/src/io/io.go:386
  22. os.genericReadFrom(0xb000000006018ab?, {0x4969a8, 0xc0000a4018})
  23. 	/usr/local/go-faketime/src/os/file.go:162 +0x67
  24. os.(*File).ReadFrom(0xc0000a4008, {0x4969a8, 0xc0000a4018})
  25. 	/usr/local/go-faketime/src/os/file.go:156 +0x1b0
  26. io.copyBuffer({0x496a28, 0xc0000a4008}, {0x4969a8, 0xc0000a4018}, {0x0, 0x0, 0x0})
  27. 	/usr/local/go-faketime/src/io/io.go:413 +0x14b
  28. io.Copy(...)
  29. 	/usr/local/go-faketime/src/io/io.go:386
  30. main.main.func1()
  31. 	/tmp/sandbox4108076976/prog.go:18 +0x71
  32. created by main.main
  33. 	/tmp/sandbox4108076976/prog.go:16 +0x1d3

Here is a playground link to the code: https://goplay.tools/snippet/70UbGIz8fTV

Is there any way to avoid the deadlock while keeping the io.Pipe?

答案1

得分: 5

当完成时，关闭管道的写入端：

  1. _, err := io.Copy(pipeWriter, read)
  2. pipeWriter.Close()
  3. if err != nil {
  4.     println(err.Error())
  5. }

如果没有这样做，读取端将会无限期等待。

英文:

Close the writing end of the pipe when done:

  1. _, err := io.Copy(pipeWriter, read)
  2. pipeWriter.Close()
  3. if err != nil {
  4.     println(err.Error())
  5. }

Without that, the reader end will wait indefinitely.

huangapple
  • 本文由 发表于 2023年1月7日 02:04:03
  • 转载请务必保留本文链接：https://go.coder-hub.com/75034559.html
  • go
  • goroutine
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