#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/sem.h>

int sem;

void *thread (int p) {
	struct sembuf op;
	op.sem_num = 0;
	op.sem_flg = 0;
	
	while (1) {
		printf("Thread %d ready\n", p);
		op.sem_op = -1;
		semop(sem, &op, 1);
		printf("Thread %d inside C.S.\n", p);
		usleep(1000000 * p);
		printf("Thread %d leaving C.S.\n", p);
		op.sem_op = 1;
		semop(sem, &op, 1);
		usleep(1000000);
	}
}

int main () {
	pthread_t thr_id;

	sem = semget(IPC_PRIVATE, 1, 0600 | IPC_CREAT);
	semctl(sem, 0, SETVAL, 1);
	
	pthread_create(&thr_id, NULL, thread, (void *) 1);
	pthread_create(&thr_id, NULL, thread, (void *) 2);
	pthread_create(&thr_id, NULL, thread, (void *) 3);
	pthread_create(&thr_id, NULL, thread, (void *) 4);
	pthread_create(&thr_id, NULL, thread, (void *) 5);
	pthread_create(&thr_id, NULL, thread, (void *) 6);
		
	usleep(50000000); //simulation time

	return 0;
}