Test SCO Xenix IPC reliability

[The Beach Bum]

Someone was screaming about how unrealiable IPC (such as shared memory)
on SCO Xenix was.  I whipped this program up originally back during the
great volatile debate and only discovered it again tonigh while cleaning
out my home directory.  When run it prints out

TICK ...
... TOCK

forever as each process gets a chance to execute.  The code is short
enough that you should be able to understand what is going on.  If
you can run this without any trouble then your shared memory is working
just fine.  Otherwise, you have troubles ...

- John.
---------------------- clip out and save as volatile.c ----------------
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <signal.h>

int	zero = 0;
int	*loc = &zero;

int	key = ('v' << 8) | 'o';

catch (sig)
int	sig;
{
	signal (sig, catch);
}

parent ()
{
	while (1) {
		while (*loc)
			;

		write (1, "TICK ....\n", 10);
		*loc = 1;
		kill (loc[2], SIGUSR1);
		pause ();
	}
}

child ()
{
	while (1) {
		while (! *loc)
			;

		write (1, ".... TOCK\n", 10);
		*loc = 0;
		kill (loc[1], SIGUSR1);
		pause ();
	}
}

main ()
{
	int	id;

	if ((id = shmget (key, 3 * sizeof (int), IPC_CREAT|0666)) == -1) {
		perror ("shmget");
		exit (1);
	}
	if ((loc = (int *) shmat (id, (char *) 0, 0)) == (int *) 0) {
		perror ("shmat");
		exit (1);
	}
	loc[0] = 0;
	switch (fork ()) {
		default:
			loc[1] = getpid ();
			signal (SIGUSR1, catch);
			parent ();
		case 0:
			loc[2] = getpid ();
			signal (SIGUSR1, catch);
			child ();
		case -1:
			perror ("fork");
			exit (1);
	}
	exit (1);
}
-- 
John F. Haugh II                 +--------- Cute Chocolate Quote ---------
HASA, "S" Division               | "USENET should not be confused with
UUCP:   killer!rpp386!jfh        |  something that matters, like CHOCOLATE"
DOMAIN: jfh at rpp386.uucp          |         -- apologizes to Dennis O'Connor