嘗試寫入/讀取時 io.Pipe 和死鎖

問題內容

我花了幾個小時嘗試理解底層邏輯，但沒有任何進展。下面的程式碼在第一次迭代後返回死鎖。如果我在 io.copy 之前關閉 writer，死鎖就會消失，但不會列印任何內容（因為管道寫入端在讀取之前已關閉）

func main() {
    reader, writer := io.pipe()
    c := make(chan string)

    go func() {
        for i := 0; i < 5; i++ {
            text := fmt.sprintf("hello %vth time", i+1)
            c <- text
        }

        close(c)
    }()

    for msg := range c {
        msg = fmt.sprintf("\nreceived from channel -> %v\n", msg)

        go fmt.fprint(writer, msg)
        io.copy(os.stdout, reader)
        writer.close()
    }

}

這是運行程式碼後的錯誤

received from channel -> hello 1th time fatal error: all goroutines
are asleep - deadlock!
goroutine 1 [select]: io.(*pipe).read(0xc000130120, {0xc00013e000,
0x8000, 0xc00011e001?})
/usr/lib/go/src/io/pipe.go:57 +0xb1 io.(*PipeReader).Read(0x0?, {0xc00013e000?, 0xc00011e050?, 0x10?})
/usr/lib/go/src/io/pipe.go:136 +0x25 io.copyBuffer({0x4bde98, 0xc00011e050}, {0x4bddb8, 0xc00012e018}, {0x0, 0x0, 0x0})
/usr/lib/go/src/io/io.go:427 +0x1b2 io.Copy(...)
/usr/lib/go/src/io/io.go:386 os.genericReadFrom(0x101c00002c500?, {0x4bddb8, 0xc00012e018})
/usr/lib/go/src/os/file.go:161 +0x67 os.(*File).ReadFrom(0xc00012e008, {0x4bddb8, 0xc00012e018})
/usr/lib/go/src/os/file.go:155 +0x1b0 io.copyBuffer({0x4bde38, 0xc00012e008}, {0x4bddb8, 0xc00012e018}, {0x0, 0x0, 0x0})
/usr/lib/go/src/io/io.go:413 +0x14b io.Copy(...)
/usr/lib/go/src/io/io.go:386 main.pipetest()
/home/stranger/source-code/golang/ipctest/pipes/main.go:39 +0x1ae main.main()
/home/stranger/source-code/golang/ipctest/pipes/main.go:10 +0x17
goroutine 18 [chan send]: main.pipetest.func1()
/home/stranger/source-code/golang/ipctest/pipes/main.go:29 +0x85 created by main.pipetest
/home/stranger/source-code/golang/ipctest/pipes/main.go:26 +0x17a exit status 2

正確答案

io.copy 不斷嘗試複製，直到讀取器到達eof（在本例中，當管道關閉時）。由於您在io.copy 結束後呼叫writer.close() after ，因此io.copy 將永遠不會看到eof，並永遠掛起。

程式碼的另一個問題是您嘗試多次關閉管道（每次循環程式碼重複時）。一般情況下，closeable 物件只應關閉一次，並且在 closed 後被假定為不可用。如果您需要重新使用它們，您應該建立一個新實例。

這是程式碼的工作修訂版：

func main() {
    c := make(chan string)

    go func() {
        for i := 0; i < 5; i++ {
            text := fmt.Sprintf("hello %vth time", i+1)
            c <- text
        }

        close(c)
    }()

    for msg := range c {
        msg = fmt.Sprintf("\nreceived from channel -> %v\n", msg)

        // Create a new pipe for this message.
        reader, writer := io.Pipe()
        go func() {
            fmt.Fprint(writer, msg)
            // Close the pipe after writing the message.
            writer.Close()
        }()

        io.Copy(os.Stdout, reader)
    }
}

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