Deadlock while waiting for piped io.Copy in Goroutine-CodePudding

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.

func main() {
    read := strings.NewReader("abcdefghij")
    pipeReader, pipeWriter := io.Pipe()

    var wg sync.WaitGroup
    wg.Add(1)
    go func() {
        println("Start copy")
        _, err := io.Copy(os.Stdout, pipeReader)
        if err != nil {
            println(err.Error())
        }
        println("End copy")
        wg.Done()
    }()

    _, err := io.Copy(pipeWriter, read)
    if err != nil {
        println(err.Error())
    }

    wg.Wait()
}

Output:

Start copy
abcdefghij
fatal error: all goroutines are asleep - deadlock!

goroutine 1 [semacquire]:
sync.runtime_Semacquire(0xc0000b0018?)
    /usr/local/go-faketime/src/runtime/sema.go:62  0x25
sync.(*WaitGroup).Wait(0x4969c8?)
    /usr/local/go-faketime/src/sync/waitgroup.go:139  0x52
main.main()
    /tmp/sandbox4108076976/prog.go:31  0x23c

goroutine 18 [select]:
io.(*pipe).read(0xc0000a6120, {0xc0000b6000, 0x8000, 0xc00009e101?})
    /usr/local/go-faketime/src/io/pipe.go:57  0xb1
io.(*PipeReader).Read(0x10?, {0xc0000b6000?, 0xc00009e1e0?, 0x4f75a0?})
    /usr/local/go-faketime/src/io/pipe.go:136  0x25
io.copyBuffer({0x496aa8, 0xc00009e1e0}, {0x4969a8, 0xc0000a4018}, {0x0, 0x0, 0x0})
    /usr/local/go-faketime/src/io/io.go:427  0x1b2
io.Copy(...)
    /usr/local/go-faketime/src/io/io.go:386
os.genericReadFrom(0xb000000006018ab?, {0x4969a8, 0xc0000a4018})
    /usr/local/go-faketime/src/os/file.go:162  0x67
os.(*File).ReadFrom(0xc0000a4008, {0x4969a8, 0xc0000a4018})
    /usr/local/go-faketime/src/os/file.go:156  0x1b0
io.copyBuffer({0x496a28, 0xc0000a4008}, {0x4969a8, 0xc0000a4018}, {0x0, 0x0, 0x0})
    /usr/local/go-faketime/src/io/io.go:413  0x14b
io.Copy(...)
    /usr/local/go-faketime/src/io/io.go:386
main.main.func1()
    /tmp/sandbox4108076976/prog.go:18  0x71
created by main.main
    /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?

CodePudding user response：

Close the writing end of the pipe when done:

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

Without that, the reader end will wait indefinitely.