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

void *thr_main(void *arg);
int value;
sem_t *sem;

int main(int argc, char *argv[]){
  pthread_t thrID[3];
  int i;

  value = 1;
  sem = (sem_t *)malloc( sizeof(sem_t) );
  sem_init(sem, 0, 1);

  for(i=0; i<3; i++)
    pthread_create(&(thrID[i]), NULL, thr_main, NULL);
  for(i=0; i<3; i++)
    pthread_join(thrID[i], NULL); 
  printf("value: %d\n",value);

  return(0);
}

void *thr_main(void *arg){
  sem_wait(sem);
  value++;
  sem_post(sem);
}