Doing job-control on you own ?

[Ole Nomann Thomsen]

Hello All.

I am trying to write a small shell-like program, that will enable me
to simulate a limited form of job-control on a system that hasn't got
it. (SCO Xenix rel. 2.3.2).

What I have in mind is this:

$ co-start prog1 prog2

Now, prog1 is active, until you generate some signal, at which
point prog1 is suspended, and prog2 starts up (and so on). To simplify
things, I will avoid detaching the suspended process from the terminal
and stuff like that.

My idea was something like this:

main()
{
	signal(SOMESIGNAL, switch);
	/* SOMESIGNAL should be something the keyboard could generate */

	if (fork() == 0) exec ("Prog1");
	if (fork() == 0) exec ("Prog2");

	/* do something else */
}

switch()
{
	static int flag;

	if (flag == MYTURN) {
		flag = NOTMYTURN;
		resume; /* probably some longjump */
	} else {
		flag = MYTURN;
		sleep (INFINITE);
	}
}

But then I realised: "Hey, the signal(SOMESIGNAL, switch) will never
survive the exec!", and I got stuck.

Isn't there some way of doing this, even when you <som'thing>IX
doesn't support job control? Or have I just asked for the impossible?

I would really appriciate help, ranging from: "You misused fork()" to:
"Ah, what you need is probably this: <CODE> Have fun.", or perhaps even:
"This is impossible because of <REASON>, you poor ignorant soul.".

Standard nettiquette applies: Please E-mail, and I'll post a summary.

- Ole. (nomann at diku.dk).

"Information is not knowledge" - Frank Zappa.