#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <signal.h>
#include <getopt.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/stat.h>

/* compile with -D_XOPEN_SOURCE=500 */

int main(int argc, char *argv[])
{
	long ps_delay = 250000, fork_delay = 100000;
	char c;
	pid_t ps_pid, pid;
	sigset_t set;

	while ((c = getopt(argc, argv, "p:f:")) != -1) {
		switch (c) {
			case 'p':
				ps_delay = strtol(optarg, NULL, 0);
				if (errno != 0 || ps_delay < 0)
					return EXIT_FAILURE;
				break;
			case 'f':
				fork_delay = strtol(optarg, NULL, 0);
				if (errno != 0 || fork_delay < 0)
					return EXIT_FAILURE;
				break;
			default:
				return EXIT_FAILURE;
		}
	}
	for (;;) {
		ps_pid = fork();
		if (ps_pid > 0)
			break;
		else if (ps_pid < 0) {
			if (errno == EAGAIN)
				errno = 0;
			else
				return EXIT_FAILURE;
		} else {
			int fd = open("/dev/null", 0);

			if (fd < 0)
				return EXIT_FAILURE;
			if (dup2(fd, STDIN_FILENO) != STDIN_FILENO)
				return EXIT_FAILURE;
			if (dup2(fd, STDOUT_FILENO) != STDOUT_FILENO)
				return EXIT_FAILURE;
			if (dup2(fd, STDERR_FILENO) != STDERR_FILENO)
				return EXIT_FAILURE;
			if (close(fd) != 0)
				return EXIT_FAILURE;
			for (;;) {
				if (system("ps -elf") == 0) {
					if (usleep(ps_delay) != 0)
						return EXIT_FAILURE;
				} else if (errno == EAGAIN)
					errno = 0;
				else
					return EXIT_FAILURE;
			}
			return EXIT_SUCCESS;
		}
	}
	sigfillset(&set);
	if (sigprocmask(SIG_BLOCK, &set, NULL) != 0)
		return EXIT_FAILURE;
	for (;;) {
		int ret;

		for (;;) {
			pid = fork();
			if (pid == 0)
				return EXIT_SUCCESS;
			else if (pid > 0)
				break;
			else if (errno != EAGAIN)
				goto cleanup_ps;
		}
		ret = waitpid(pid, NULL, 0);
		if (ret == -1)
			goto cleanup_ps;
		/* check up on ps child */
		ret = waitpid(ps_pid, NULL, WNOHANG);
		/*
		 * panic and leave mess on error
		 * or exit without doing anything if ps child died
		 */
		if (ret == -1 || ret == ps_pid)
			return EXIT_FAILURE;
		sigfillset(&set);
		if (sigpending(&set) != 0)
			goto cleanup_ps;
		if (sigismember(&set, SIGHUP)
				|| sigismember(&set, SIGINT)
				|| sigismember(&set, SIGQUIT)
				|| sigismember(&set, SIGILL)
				|| sigismember(&set, SIGABRT)
				|| sigismember(&set, SIGFPE)
				|| sigismember(&set, SIGKILL)
				|| sigismember(&set, SIGSEGV)
				|| sigismember(&set, SIGPIPE)
				|| sigismember(&set, SIGALRM)
				|| sigismember(&set, SIGTERM)
				|| sigismember(&set, SIGUSR1)
				|| sigismember(&set, SIGUSR2)
				|| sigismember(&set, SIGSTOP)
				|| sigismember(&set, SIGTSTP)
				|| sigismember(&set, SIGTTIN)
				|| sigismember(&set, SIGTTOU))
			goto cleanup_ps;
		if (usleep(fork_delay) != 0)
			goto cleanup_ps;
	}
	return EXIT_SUCCESS;
cleanup_ps:
	/* clean up ps child, ignoring errors */
	kill(ps_pid, SIGKILL);
	waitpid(ps_pid, NULL, 0);
	return EXIT_FAILURE;
}