How do I write an async child reaper in Go?

Question

I have some go code like this:

cmd = exec.Command(command)
//...
cmd.Run()
func reapChild(cmd) {
    sigc := make(chan os.Signal, 1)
    signal.Notify(sigc, syscall.SIGCHLD)
    go func() {
        my_signal := <- sigc
        log.Infof("appstore: reapChildren: got a SIGCHLD signal")
        cmd.Wait()
        signal.Stop(sigc)
    }()
}

This reaps the process for a specific spawned child, but I'm looking for something more generic.

Is there a way to get the PID off my_signal? I'm looking for something like the pid_t wait(int *status) -- golang provides a function called Wait4 that takes a specific PID.

Answer 1

As you say, Go's syscall package has this function:

func Wait4(pid int, wstatus *WaitStatus, options int, rusage *Rusage) (wpid int, err error)

That seems to work for you. From the BSD man page for wait(2) (remember that Go was developed partly on Macs!):

The wait4() call provides a more general interface for programs that need to wait for certain child processes, that need resource utilization statistics accumulated by child processes, or that require options. The other wait functions are implemented using wait4().

By passing the right arguments, you can achieve what you want with Wait4. For example, if you don't want to wait for a specific child:

If pid is -1, the call waits for any child process.

You can find the rest of the information you need in the man page.