CODEWITHSUNDEEP
gosignals
MakotoE
MakotoE

Reputation: 2109

How do I send a signal to a child process?

I'm having trouble sending a signal from a parent process and receiving it in the child process.

This is the code for the child process. It exits when it receives SIGINT.

// child.go
func main() {
    stop := make(chan os.Signal, 1)
    signal.Notify(stop, os.Interrupt)
    fmt.Println("started")

    <-stop
    fmt.Println("stopped")
}

This is the parent process. It starts child.go, sends SIGINT, then waits for it to exit.

// main.go
func main() {
    // Start child process
    cmd := exec.Command("go", "run", "child.go")
    cmd.Stdout = os.Stdout
    cmd.Stderr = os.Stderr
    err := cmd.Start()
    if err != nil {
        _, _ = fmt.Fprintf(os.Stderr, "Start: " + err.Error())
        return
    }

    // Wait, then send signal
    time.Sleep(time.Millisecond * 500)
    err = cmd.Process.Signal(os.Interrupt)
    if err != nil {
        _, _ = fmt.Fprintf(os.Stderr, "Signal: " + err.Error())
        return
    }

    // Wait for child process to finish
    err = cmd.Wait()
    if err != nil {
        _, _ = fmt.Fprintf(os.Stderr, "Wait: " + err.Error())
    }
    return
}

This code should print started\nstopped to show that it worked as expected, but it only prints started and hangs at cmd.Wait(), meaning the child process did not receive the signal.

When I run go run child.go it works fine, so I don't think the problem is with that file. I understand that func (*Process) Signal doesn't work on Windows; I am using Linux.

How can I fix the code so that the child process gets the signal sent by the parent process?

Upvotes: 3

Views: 4726

Answers (1)

thst
thst

Reputation: 4602

As mentioned by @JimB in the comments section, the go run is your problem.

go run child.go will compile child and execute it as it's own process. If you run a ps after go run child.go, you will see two processes running.

The process you are watching and signalling is the go executable, not the child.

Replace the exec.Command("go", "run", "child.go") with the compiled binary exec.Command("child")and it should work.

Upvotes: 5

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