#include <stdio.h>	/* simula un semaforo usando mutex e variabili condizione */
#include <pthread.h>
#include <semaphore.h>

typedef struct {
  	pthread_mutex_t mutex;
  	pthread_cond_t cond;
  	int counter;
} mysem_t;
mysem_t mysem;

void unlock_mutex(void *m)
{   pthread_mutex_unlock((pthread_mutex_t *)m); }

void mysem_init(mysem_t *s, int num) {
  	pthread_mutexattr_t m;
  	pthread_condattr_t c;

  	s->counter = num;
  	pthread_mutexattr_init(&m);
  	pthread_mutex_init(&s->mutex, &m);
  	pthread_mutexattr_destroy(&m);
  	pthread_condattr_init(&c);
  	pthread_cond_init(&s->cond, &c);
  	pthread_condattr_destroy(&c);
}

void mysem_wait(mysem_t *s) {
	pthread_mutex_lock(&s->mutex);
  	while (!(s->counter)) pthread_cond_wait(&s->cond, &s->mutex);
  	
  	s->counter--;
  	pthread_mutex_unlock(&s->mutex);
}

void mysem_post(mysem_t *s) {
  	pthread_mutex_lock(&s->mutex);
  	if (!(s->counter++)) pthread_cond_signal(&s->cond);

  	pthread_mutex_unlock(&s->mutex);
}
void *body(void *arg) {
  	int i,j;
mysem_wait(&mysem);
  	for (j=0; j<40; j++) {
    		
    		for (i=0; i<1000000; i++);  printf("%c",*(char *)arg);
    		
  	}
mysem_post(&mysem);
  	return NULL;
}

int main() {
  	pthread_t t1,t2,t3;
  	pthread_attr_t myattr;
  	int err;

  	mysem_init(&mysem,1);
  	pthread_attr_init(&myattr);
  	err = pthread_create(&t1, &myattr, body, (void *)".");
  	err = pthread_create(&t2, &myattr, body, (void *)"#");
  	err = pthread_create(&t3, &myattr, body, (void *)"o");
  	pthread_attr_destroy(&myattr);

  	pthread_join(t1, NULL);  pthread_join(t2, NULL);   pthread_join(t3, NULL);
  	printf("\n");   	return 0;
}