#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>

int main ( int argc, char *argv[] )
{
   int rshmid, wshmid, *p;
   int r_mutex, w_mutex, block_read, block_write;

   if (argc == 1) {
      fprintf(stderr, "*** Run with command: create or remove\n");
      exit(1);
   }

   if (!strcmp(argv[1], "create")) {
      rshmid = shmget(ftok("/home",1), sizeof(int), 0666 | IPC_CREAT | IPC_EXCL);
      p = (int *)shmat(rshmid, NULL, 0); *p = 0;
      shmdt(p);
      wshmid = shmget(ftok("/home",2), sizeof(int), 0666 | IPC_CREAT | IPC_EXCL);
      p = (int *)shmat(wshmid, NULL, 0); *p = 0;
      shmdt(p);

      r_mutex = semget(ftok("/home",3), 1, 0666 | IPC_CREAT | IPC_EXCL);
      semctl(r_mutex, 0, SETVAL, 1);
      w_mutex = semget(ftok("/home",4), 1, 0666 | IPC_CREAT | IPC_EXCL);
      semctl(w_mutex, 0, SETVAL, 1);
      block_read = semget(ftok("/home",5), 1, 0666 | IPC_CREAT | IPC_EXCL);
      semctl(block_read, 0, SETVAL, 1);
      block_write = semget(ftok("/home",6), 1, 0666 | IPC_CREAT | IPC_EXCL);
      semctl(block_write, 0, SETVAL, 1);
   } else if (!strcmp(argv[1], "remove")) {
      rshmid = shmget(ftok("/home",1), sizeof(int), 0666);
      wshmid = shmget(ftok("/home",2), sizeof(int), 0666);

      r_mutex = semget(ftok("/home",3), 1, 0666);
      w_mutex = semget(ftok("/home",4), 1, 0666);
      block_read = semget(ftok("/home",5), 1, 0666);
      block_write = semget(ftok("/home",6), 1, 0666);

      printf("\t\t\tHit return when all readers and writers are gone\n");
      while (getchar() != '\n') ;

      shmctl(rshmid, IPC_RMID, NULL);
      shmctl(wshmid, IPC_RMID, NULL);

      semctl(r_mutex, 0, IPC_RMID, 0);
      semctl(w_mutex, 0, IPC_RMID, 0);
      semctl(block_read, 0, IPC_RMID, 0);
      semctl(block_write, 0, IPC_RMID, 0);
   }

   exit(0);
}