#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>


#define TRUE	1
#define FALSE	0
typedef void              (*sigfunc_t)();


int QueueIntvl = 4;
volatile int DoQueueRun;
volatile int tick_cnt = 0;
volatile int child_cnt = 0;

sigfunc_t
setsignal(sig, handler)
	int sig;
	sigfunc_t handler;
{
	return signal(sig, handler);
}


int
blocksignal(sig)
	int sig;
{
	sigset_t sset, oset;

	sigemptyset(&sset);
	sigaddset(&sset, sig);
	if (sigprocmask(SIG_BLOCK, &sset, &oset) < 0)
	{
		perror ("sigprocmask");
		exit (1);
	}
	else
		return sigismember(&oset, sig);
}


int
releasesignal(sig)
	int sig;
{
	sigset_t sset, oset;

	sigemptyset(&sset);
	sigaddset(&sset, sig);
	if (sigprocmask(SIG_UNBLOCK, &sset, &oset) < 0)
	{
		perror ("sigprocmask");
		exit (1);
	}
	else
		return sigismember(&oset, sig);
}

void
tick(int sig)
{
	tick_cnt++;
	DoQueueRun = TRUE;
}


void
setevent(intvl)
	time_t intvl;
{
	int wasblocked;

	wasblocked = blocksignal(SIGALRM);

	setsignal(SIGALRM, tick);
	(void) alarm((unsigned) intvl);
	if (wasblocked == 0)
		(void) releasesignal(SIGALRM);
	printf ("Requested tick\n");
}


void
reapchild(int sig)
{
	pid_t pid;
	int status;

	child_cnt++;
	pid = waitpid(-1, &status, WNOHANG);
	if (pid <= 0)
	{
		printf("waitpid failed!\n");
		exit (1);
	}
}


int
runqueue(void)
{
	pid_t pid;

	printf ("Setting DoQueueRun FALSE\n");
	DoQueueRun = FALSE;

	blocksignal(SIGCHLD);
	(void) setsignal(SIGCHLD, reapchild);

	pid = fork();
	if (pid == -1)
	{
		perror ("fork");
		exit (1);
	}
	if (pid != 0)
	{
		/* parent -- pick up intermediate zombie */
		printf("Child %d\n", pid);
		releasesignal(SIGCHLD);
		setevent(QueueIntvl);
		return TRUE;
	}
	/* Child exits */
	exit (0);
}


int
main (int argc, char **argv)
{
	int cnt = 0;
	int last_tick_cnt, last_child_cnt, new_tick_cnt, new_child_cnt;

	runqueue();
	for (;;)
	{
		printf ("Pause %d\n", cnt++);
		last_tick_cnt = tick_cnt;
		last_child_cnt = child_cnt;
		pause();
		new_tick_cnt = tick_cnt;
		new_child_cnt = child_cnt;
		if (last_tick_cnt == new_tick_cnt && last_child_cnt == new_child_cnt)
		{
			int loop = 0;
			printf ("Hmm, seems we came off pause for no reason.\n");
			printf ("Looping waiting for sig hander to finish\n");
			while (last_tick_cnt == tick_cnt && last_child_cnt == child_cnt)
				loop++;
			printf ("Handler ran, loop %d (tick %d -> %d, child %d -> %d)\n",
				loop, last_tick_cnt, tick_cnt, last_child_cnt, child_cnt);
		}

		if (DoQueueRun)
			(void) runqueue();
		else
			printf ("DoQueueRun FALSE (tick %d -> %d, child %d -> %d)\n",
				last_tick_cnt, tick_cnt, last_child_cnt, child_cnt);
	}
	return 0;
}