Semaphores

The Dining Philosophers Problem

`c++
typedef struct __Zem_t {
int value;
pthread_cont_t cond;
phtread_mutex_t lock;
} Zem_t;

void Zem_init(Zem_t *s, int value) {
s -> value = value;
Cond_init(&s -> cond);
Mutex_init(&s -> lock);
}

void Zem_wait(Zem_t *s) {
Mutex_lock(&s -> lock);
while (s->value <= 0) {
Cond_wait(&s->cond, &s->lock);
}
s->value –;
Mutex_unlock(&s->lock);
}

void Zem_post(Zem_t *s) {
Mutex_lock(&s -> lock);
s->value ++;
Cond_signal(&s->cond);
Mutex_unlock(&s->lock);
}