#include    <stdio.h>
#include    <string.h>	/* bzero */
#include    <signal.h>
#include    <unistd.h>
#include    <pthread.h>

#define NPROC	2

int inter[NPROC];
int cnt[NPROC];
int turn;

/* Stolen from BSD libkern */
#define	timevalcmp(tvp, uvp, cmp)					\
	(((tvp)->tv_sec == (uvp)->tv_sec) ?				\
	    ((tvp)->tv_usec cmp (uvp)->tv_usec) :			\
	    ((tvp)->tv_sec cmp (uvp)->tv_sec))

static void
timevalfix(t1)
	struct timeval *t1;
{

	if (t1->tv_usec < 0) {
		t1->tv_sec--;
		t1->tv_usec += 1000000;
	}
	if (t1->tv_usec >= 1000000) {
		t1->tv_sec++;
		t1->tv_usec -= 1000000;
	}
}

void
timevalsub(t1, t2)
	struct timeval *t1, *t2;
{

	t1->tv_sec -= t2->tv_sec;
	t1->tv_usec -= t2->tv_usec;
	timevalfix(t1);
}
/* end stolen */

void
finish(void)
{
    register int    i;

    putchar('\n');
    for (i = 0; i < NPROC; ++i)
	printf("proc %d: %d\n", i, cnt[i]);
    exit(0);
}

void
catch_intr(int sig)
{
    finish();
}

void
enter_crit(int pn)
{
    inter[pn] = 1;
    turn = pn;
    while (turn == pn && inter[1 - pn])
	;
}

void
leave_crit(int pn)
{
    inter[pn] = 0;
}

/* Not sure how well this actually works - */
void
synch(int pn)
{
    inter[pn] = 0;
    while (inter[1 - pn])
	;
    /*printf("synch\n");*/
}

void
busy_sleep(long usecs)
{
    long	    stime;
    struct timeval  tv, itv, stv, ztv;

    itv.tv_usec = usecs;
    itv.tv_sec = 0;
    gettimeofday(&stv, NULL);
    do
    {
	gettimeofday(&tv, NULL);
	timevalsub(&tv, &itv);
    }
    while (timevalcmp(&tv, &stv, <));
}

void
*run(void *ppn)
{
    int	pn = (int)ppn;

    synch(pn);
    /*printf("Starting thread %d\n", pn);*/
    while (cnt[pn] < 10000)
    {
	enter_crit(pn);
	++cnt[pn];
	leave_crit(pn);
	busy_sleep(250);
    }
    finish();
}

int
main(int ac, char *av[])
{
    pthread_t	pt1, pt2;

    turn = 0;
    inter[0] = inter[1] = 1;
    bzero(cnt, sizeof(cnt));
    signal(SIGINT, catch_intr);
    pthread_create(&pt1, NULL, run, (void *)0);
    pthread_create(&pt2, NULL, run, (void *)1);
    pthread_exit(NULL);
    return 0;	/* NOTREACHED */
}