There might be. Or I might be holding it wrong. I'm about to post another
thread with a different angle on this. This thread was mis-framed.
On Mon, Jun 17, 2024 at 1:16 PM Harri L <harl...@gmail.com> wrote:
> I’m wondering if there’s a specific reason you’re using io.Pipe instead
> of the Cmd.StdoutPipe helper? When using io.Pipe you need to Close the
> pipe by yourself, but when using the Cmd.StdoutPipe, the Cmd.Wait will
> close the pipe for you.
>
> Here’s a sample following your previous example:
> func main() { defer err2.Catch() cmdName := "/bin/sh" cmdArgs := []string{
> "-c", "for i in 1 2 3 4 5 6 7 8 9 10; do echo step $i; sleep 0.1; done",
> } cmd := exec.CommandContext(context.Background(), cmdName, cmdArgs...)
> stdoutPipe := try.To1(cmd.StdoutPipe()) var wg sync.WaitGroup go
> readPipe(stdoutPipe, &wg) try.To(cmd.Start()) wg.Wait() try.To(cmd.Wait())
> fmt.Println("DONE") } func readPipe(src io.Reader, wg *sync.WaitGroup) {
> defer err2.Catch() wg.Add(1) defer wg.Done() buf := make([]byte, 256) for
> eof, n := try.IsEOF1(src.Read(buf)); !eof; eof, n =
> try.IsEOF1(src.Read(buf)) { try.To1(os.Stdout.Write(buf[:n])) } }
>
> And here’s a sample using io.Pipe; please see the noted line:
> func main() { defer err2.Catch() cmdName := "/bin/sh" cmdArgs := []string{
> "-c", "for i in 1 2 3 4 5 6 7 8 9 10; do echo step $i; sleep 0.1; done",
> } cmdStdoutR, cmdStdoutW := io.Pipe() cmd :=
> exec.CommandContext(context.Background(), cmdName, cmdArgs...) cmd.Stdout =
> cmdStdoutW var wg sync.WaitGroup go readPipe(cmdStdoutR, &wg)
> try.To(cmd.Run()) cmdStdoutW.Close() // NOTE: needed for io.Pipe ↓
> fmt.Println("DONE") wg.Wait() }
>
> On Monday, June 17, 2024 at 6:21:13 AM UTC+3 Salvatore Domenick Desiano
> wrote:
>
>> Ah!
>>
>> I apologize... in reducing it to a compact example I didn't notice that I
>> changed the semantics of what the code was doing. You are, of course, right
>> about the cause of the deadlock in this code.
>>
>> That said, working backward from the self-contained example to my full
>> code clarified the actual issue I'm debugging. It is sufficiently different
>> from what I said here that I will start a new thread if I can't figure it
>> out myself.
>>
>> Thank you!
>>
>> -- Salvatore
>> smile.
>>
>>
>> On Sun, Jun 16, 2024 at 10:35 PM Robert Engels <ren...@ix.netcom.com>
>> wrote:
>>
>>> It hangs because cmd.Run() waits for the process to complete - and with
>>> nothing reading the pipe it will never complete.
>>>
>>> On Jun 16, 2024, at 9:33 PM, Robert Engels <ren...@ix.netcom.com> wrote:
>>>
>>>
>>> It looks like you don’t have anything reading from the pipe so it’s
>>> going to hang.
>>>
>>> On Jun 16, 2024, at 8:54 PM, Salvatore Domenick Desiano <
>>> near...@gmail.com> wrote:
>>>
>>>
>>> Simpler self-contained example, same result:
>>>
>>> func main() {
>>>
>>> cmdName := "/bin/bash"
>>> cmdArgs := []string{"-c", "while true; do echo step; sleep 1; done"}
>>>
>>> cmdStdoutR, cmdStdoutW := io.Pipe()
>>> cmd := exec.Command(cmdName, cmdArgs...)
>>> cmd.Stdout = cmdStdoutW
>>> if err := cmd.Run(); err != nil {
>>>
>>> fmt.Println(err)
>>>
>>> }
>>> fmt.Println("DONE")
>>>
>>> cmdStdoutR = cmdStdoutR
>>>
>>> }
>>>
>>> For the sake of completeness I'll mention that this runs fine if
>>> cmd.Stdout is not assigned, which points to exec.awaitGoroutines() as being
>>> the culprit.
>>>
>>> FWIW, I have no direct evidence that the pipes aren't being closed on
>>> the SIGKILL. That said, the (exec-internal) goroutines are hung on
>>> io.Copy(). I expect that if the process's output pipe was actually closed
>>> the io.Copy() would return, the goroutine would complete, and the deadlock
>>> would not happen.
>>>
>>> -- Salvatore
>>> smile.
>>>
>>>
>>> On Sun, Jun 16, 2024 at 7:58 PM Salvatore Domenick Desiano <
>>> near...@gmail.com> wrote:
>>>
>>>> I hope this isn't a red herring but in constructing a self-contained
>>>> example I triggered a deadlock. Perhaps the deadlock is the answer to my
>>>> question or perhaps it is another issue. Either way this code does not seem
>>>> malformed:
>>>>
>>>> func main() {
>>>>
>>>> cmdName := "/bin/bash"
>>>> cmdArgs := []string{
>>>>
>>>> "-c",
>>>>
>>>> "while true; do echo step; sleep 1; done",
>>>>
>>>> }
>>>> cmdStdinR, cmdStdinW := io.Pipe()
>>>> cmdStdoutR, cmdStdoutW := io.Pipe()
>>>> cmdStderrR, cmdStderrW := io.Pipe()
>>>> ctx, cancelCmd := context.WithCancel(context.Background())
>>>> cmd := exec.CommandContext(ctx, cmdName, cmdArgs...)
>>>> cmd.Stdin = cmdStdinR
>>>> cmd.Stdout = cmdStdoutW
>>>> cmd.Stderr = cmdStderrW
>>>>
>>>> if err := cmd.Start(); err != nil {
>>>>
>>>> fmt.Println(err)
>>>>
>>>> }
>>>>
>>>> cmdStdinW.Close()
>>>> if err := cmd.Wait(); err != nil {
>>>>
>>>> fmt.Println(err)
>>>>
>>>> }
>>>>
>>>> fmt.Println("DONE")
>>>>
>>>> cancelCmd = cancelCmd
>>>> cmdStdoutR = cmdStdoutR
>>>> cmdStderrR = cmdStderrR
>>>>
>>>> }
>>>>
>>>> If you run this code and SIGKILL the bash process, go flags it as a
>>>> deadlock and panics. FWIW, this also happens if there are goroutines
>>>> monitoring cmdStdoutR and cmdStderrR.
>>>>
>>>> What am I missing?
>>>>
>>>> -- Salvatore
>>>> smile.
>>>>
>>>>
>>>> --
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