#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <fcntl.h>

struct shared {
	int a, b;
};

#define SM_NAME  "/sm_example_name"  /* created in /dev/shm/ */
#define SM_SIZE  sizeof (struct shared)
#define PROC_NUM 10

void process(int app_id)
{
	int id, tmp;
	struct shared *x;

	sleep(app_id); /* sync by sleep */

	/* create/open shared memory object; map it to memory */
	id = shm_open(SM_NAME, O_CREAT | O_RDWR, 00600);
	if (id == -1 || ftruncate(id, SM_SIZE) == -1) {
		perror("shm_open/ftruncate");
		exit(1);
	}
	x = mmap(NULL, SM_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, id, 0);
	if (x == (void *) -1) {
		perror("mmap");
		exit(1);
	}
	close(id);

	if (app_id == 0) {
		x->a = 0;
		x->b = 1;
	} else {
		tmp = x->a + x->b;
		x->a = x->b;
		x->b = tmp;
	}
	printf("[%d] %d\n", app_id+1, x->b);

	/* last process should delete shared memory */
	if (app_id == PROC_NUM-1) {
		munmap(x, SM_SIZE);
		shm_unlink(SM_NAME);
	}
}

int main(void)
{
	int i;

	for (i = 0; i < PROC_NUM; i++)
		if (!fork()) {
			process(i);
			exit(0);
		}
	for (i = 0; i < PROC_NUM; i++)
		wait(NULL);

	return 0;
}