#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>

volatile long cnt = 0; /* Counter */
sem_t *s; /* Semaphore that protects counter */

void *thread(void *vargp){
  long i, niters =    *((long *)vargp);
  for (i = 0; i < niters; i++){
    sem_wait(s); /* P(s) */
    cnt++;                   
    sem_post(s); /* V(s) */
  }
  return NULL;
} 

int main(int argc, char **argv)
{
  long niters;
  pthread_t tid1, tid2;

  s = sem_open("semaphore",O_CREAT, 0644, 1);

  niters = atoi(argv[1]);
    pthread_create(&tid1, NULL, thread, &niters);
    pthread_create(&tid2, NULL, thread, &niters);
    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);

  /* Check result */
  if (cnt != (2 * niters))
    printf("BOOM! cnt=%ld\n", cnt);
  else
    printf("OK cnt=%ld\n", cnt);
  exit(0);
}