I don't need to read from the process, just write to it. I know open2() returns PID. I am specifically using open2() because it returns a PID and I am able to write to the process. But maybe I can do that like you said.

I know I can open the handle globally (ie; before I fork), but I couldn't figure out how to work it into the code I wrote so that the flow works out to how it should.

Thing is, I need to be able to write to the binary process, whilst also checking to see if it exists, if it doesn't, I need to restart it.

If the binary process terminates for some reason, it must be restarted. But if I want to actually end the binary process, I need to kill off the parent(s). I couldn't see that this would work with what I had done unless I just send it a catchable SIGNAL. Of course if one were to send a SIGKILL signal to the parent, it wouldn't be catchable. Sure it will terminate it, but the binary process would still remain.

I will try some stuff and re-post it.

And here is a solution :

------------------------------------

use POSIX ":sys_wait_h"; # Didn't do this before.
my $spid;
print "Launching \"$actual_prog\" as UID($uid)/GID($gid)\n";

    unless (my $pid=fork()) {
        # Re-direct $program's STDERR to a file on the hard disk
        open(STDERR,">> $logfile"); 
        $spid = open2(*SREAD, *SWRITE, "$program @prog_options");
        while(1) {
            if($got_sig==1) {
                print STDOUT "GOT SIGNAL on $0\n";
                print SWRITE "Hey there server process\n";
                sleep 0.5;
                kill('KILL',$spid);
                exit(0);
            }else{
                    my $der = waitpid($spid,WNOHANG);
                    # If return val < 0. It ended ...
                    if($der==-1) {
                        print STDOUT "Time to re-launch\n";
                        open(STDERR,">> $logfile");
                        $spid = open2(*SREAD, *SWRITE, "$program @prog
+_options");
                    }
            }
        }
    }
[download]

------------------------------------

Obviously I am only using one Perl process to manage the spawned binary process now. I also specifically included sys_wait_h : use POSIX ":sys_wait_h";, which I hadn't done before. Now the following works fine :

my $der = waitpid($spid,WNOHANG);
                    if($der==-1) {
                        print STDOUT "Time to re-launch\n";
                        open(STDERR,">> $logfile");
                        $spid = open2(*SREAD, *SWRITE, "$program @prog
+_options");
                    }
[download]

and I can do other stuff whilst the child process state hasn't changed (ie; actually non-blocking waitpid()).

This works fine for me. But I liked my other code. Oh well. Whatever works. I should probably re-read over waitpid() and how Perl implements it.