Hi,

I have problem with my functions. Sometimes two processes enter into critical section. I can't find problem in this after I spent 10 hours by debugging. On what I should aim?

    // lock semaphore
    static int P(int sem_id)
    {
        struct sembuf sem_b;
        sem_b.sem_num = 0;
        sem_b.sem_op = -1; /* P() */
        sem_b.sem_flg = 0;
        if (semop(sem_id, &sem_b, 1) == -1) {
        print_error("semop in P", errno);
        return(0);
        }
        return(1);
    }

    // unlock semaphore
    static int V(int sem_id)
    {
        struct sembuf sem_b[1];
        sem_b.sem_num = 0;
        sem_b.sem_op = 1; /* V() */
        sem_b.sem_flg = 0;
        if (semop(sem_id, &sem_b, 1) == -1) {
            print_error("semop in V", errno);
            return(0);
        }
        return(1);
    }

The action loop:

int mutex;
if ((mutex=semget(key, 1, 0666))>=0) {
    // semaphore exists
}
while(1) {
        P(mutex);   
        assert(get_val(mutex)==0);
        (*action)++;
        V(mutex);
}   

Many thanks