//
// Program to create shared semaphores
//

#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/shm.h>
#include <sys/wait.h>
#include <unistd.h>

int main() {
  int shmid, pid;
  sem_t *sem;

  shmid = shmget(IPC_PRIVATE, sizeof(sem_t), IPC_CREAT | 0600);
  sem = (sem_t *)shmat(shmid, NULL, 0);

  sem_init(sem, 1, 0);

  if ((pid = fork()) != 0) {
    printf("Parent!. Making my child wait for 1 second.\n");
    sleep(1);
    sem_post(sem);
    wait(NULL);
    sem_destroy(sem);
    shmctl(shmid, IPC_RMID, 0);
  } else {
    sem_wait(sem);
    printf("Child! Waited 1 second for parent.\n");
  }
}
