/* Program to demonstrate shared memory IPC  */
/* Written by Carey Williamson  Jan 27, 2010 */

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

#define DEBUG 1
#define SLOW 1

int main()
  {
    pid_t pid;
    int i, num = 0;

    /* fork a child process */
    pid = fork();

    if( pid < 0 )
      {
	/* error occurred */
	fprintf(stderr, "Fork failed!\n");
	return 1;
      }
    else if( pid == 0 )
      {
	/* child process */
#ifdef DEBUG
	printf("\t\t\t\tI am the child! Here I go...\n");
#endif
#ifdef SLOW
        sleep(1);
#endif
	printf("\t\t\t\tChild process: num = %d\n", num);
	num = 1;
	printf("\t\t\t\tChild process sets num = %d\n", num);
#ifdef SLOW
        sleep(3);
#endif
	printf("\t\t\t\tChild process: num = %d\n", num);
	num = 3;
	printf("\t\t\t\tChild process sets num = %d\n", num);
#ifdef SLOW
        sleep(5);
#endif
	printf("\t\t\t\tChild process: num = %d\n", num);
	num = 5;
	printf("\t\t\t\tChild process sets num = %d\n", num);

#ifdef SLOW
        sleep(7);
#endif
	printf("\t\t\t\tThat was fun! All done now.\n");
      }
    else
      {
	/* parent process */
#ifdef DEBUG
	printf("I am the parent!\n");
#endif
#ifdef SLOW
        sleep(2);
#endif
	printf("Parent process: num = %d\n", num);
	num = 2;
	printf("Parent process sets num = %d\n", num);

#ifdef SLOW
        sleep(4);
#endif
	printf("Parent process: num = %d\n", num);
	num = 4;
	printf("Parent process sets num = %d\n", num);

#ifdef DEBUG
	printf("Waiting for child now...\n");
#endif
	wait(NULL);
#ifdef DEBUG
	printf("All done, and my child too!\n");
#endif
      }
  }