#include <semaphore.h>
#include <sys/types.h>

#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>

static int timed_out = 0;

void timeout(int sig)
{
	timed_out = 1;
}

int main()
{
	static const char* sem_name = "/myhappysemaphore";
	sem_t* ps = sem_open(sem_name, O_RDWR);
	if (ps) sem_close(ps);	// clean up old semaphore; we probably crashed
	ps = sem_open(sem_name, O_CREAT, 0600, 0);
	if (ps == SEM_FAILED) {
		perror("sem_open");
		return 1;
	}
	puts("Created semamphore.");

	pid_t pid = fork();
	switch (pid) {
		case -1:	// error
			perror("fork");
			return 2;

		case 0:		// child
			signal(SIGALRM, timeout);
			while (1) {
				alarm(1);
				int ret = sem_wait(ps);
				if (ret == -1) {
					if (timed_out) {
						if (errno == EINTR) {
							puts("Child timed out normally waiting "
									"for the semaphore.");
							timed_out = 0;
						}
						else {
							puts("Child timed out ABNORMALLY waiting "
									"for the semaphore!");
							exit(99);
						}
					}
					else {
						perror("sem_wait");
						exit(69);
					}
				}
				else {
					puts("Child got the semaphore!  "
							"How the spit did that happen?");
					exit(42);
				}
			}
			break;

		default: {	// parent
			puts("Created child.  Posting the deathwatch.");
			int status;
			while (1) {
				pid_t ret = waitpid(pid, &status, 0);
				if (ret > 0) {
					if (WIFEXITED(status)) {
						printf("Child %d died peacefully, code %d.\n",
								ret, WEXITSTATUS(status));
						break;
					}
					else {
						printf("Child %d died screaming, status 0x%08X.\n",
								ret, status);
						return 3;
					}
				}
				else {
					perror("waitpid");
					return 4;
				}
			}
		}
	}

	return 0;
}