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 <reng...@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 <reng...@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 <
> neard...@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 <
> neard...@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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