#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

#define KEY 12

union semun 
{
    int val;
    struct semid_ds *buf;
    unsigned short *array;
};

int main()
{
  int sem_id;
  int i;
 
  printf("PID = **%d**\n",getpid());

  // CREATE SEMAPHORE
  sem_id = semget((key_t)KEY, 1, IPC_CREAT); 

  printf("Semaphore id = %d\n",sem_id);

  // INITIALIZE SEMAPHORE to 1
  union semun cmd1;
  cmd1.val = 1; //any value.
  if(semctl(sem_id, 0, SETVAL, cmd1) == 0) 
    printf("Semaphore SETVAL to %d SUCCESSFUL.\n",cmd1.val);
  else
    {
      printf("Semaphore SETVAL FAILED\n");
      exit(EXIT_FAILURE);
    }


  struct sembuf sem_p = {0,-1,SEM_UNDO};

  // SEMAPHORE P Operation
  if(semop(sem_id, &sem_p, 1) == -1)
  {
    printf("Semaphore P operation FAILED.\n");
    exit(EXIT_FAILURE);
  }
  else
  {
    printf("Process %d >>>>entering critical section>>>>\n",getpid());
  }

  for(i=0;i<10;i++)
    {
      printf("%d\n",i);
      sleep(1);
    }

  struct sembuf sem_v = {0,1, SEM_UNDO};

  // SEMAPHORE V Operation
  if(semop(sem_id, &sem_v, 1) == -1)
  {
    printf("Semaphore V operation FAILED.\n");  
    exit(EXIT_FAILURE);
  }
  else
  {
    printf("Process %d <<<<leaving critical section<<<<\n",getpid());
  }

  // DELETE SEMAPHORE
  union semun cmd2;
  if(semctl(sem_id, 0, IPC_RMID,cmd2) == 0)
    printf("Process %d deleted semaphore %d.\n",getpid(),sem_id);
  else
    printf("Process %d failed to delete semaphore %d.\n",getpid(),sem_id);
 
  exit(EXIT_SUCCESS);
}