/*semaphore.c*/
#include <fcntl.h>           /* For O_* constants */
#include <sys/stat.h>        /* For mode constants */
#include <semaphore.h>
#include <stdio.h>

int main(int argc, char * argv[]){
  char *name = "my_semaphore";
  int VALUE = 2;
  sem_t *sema;
  //If semaphore with name does not exist, then creat it with VALUE
  printf("Open or Creat a named semaphore, %s, its value is %d\n", name,VALUE);
  sema = sem_open(name, O_CREAT, 0666, VALUE);
  sem_wait(sema);
  printf("Decrease semaphore by 1\n");
  sem_post(sema);
  printf("Add semaphore by 1\n");
  //Befor exit, you need to close semaphore and unlink it, when all  processes have
  //finished using the semaphore, it can be removed from the system using sem_unlink
  sem_close(sema);
  sem_unlink(name);
  return 0;
}