#include <unistd.h>
#include <stdio.h>
#include <sys/stat.h>

#include <sys/shm.h>

#define NO_BUFFER ((char *)-1)
#define NONE (-1)

extern void byee(int);

class Shared {
   pid_t pid;
   int shm_id;
   char *shm_base;
public:
   void * allocate(int size);
   void destroy(void);
};

void * Shared::allocate(int size) {
      shm_id = shmget(IPC_PRIVATE, size,
                      IPC_CREAT | S_IREAD | S_IWRITE);
      if (shm_id < 0) {
         perror ("Shared::allocate shmget");
         byee (-1);
      }
      shm_base = shmat (shm_id, (char *)0, 0);
      if (shm_base == NO_BUFFER){
         perror ("Shared::allocate shmat");
         byee (-1);
      }
      pid = getpid();
      return (void *) shm_base;
   };

void Shared::destroy(void) {

      /* Buffer not yet created */
      if (shm_id == NONE) return;

      if (shmdt (shm_base) == -1)
         perror ("Shared::destroy shmdt");

      if (getpid() != pid) return;   /* only the creator should remove */

      if (shmctl (shm_id, IPC_RMID, (struct shmid_ds *)0) == -1){
         perror ("Shared::destroy shmctl");
      }
   };