#include <stdlib.h>
#include <stdio.h>
#include <sys/mman.h>
#include <sys/stat.h>        /* For mode constants */
#include <fcntl.h>           /* For O_* constants */
#include <unistd.h>
#include <sys/mman.h>

#define DEBUG 1

#ifdef DEBUG
#define dprintf(format, ...) printf(format, ##__VA_ARGS__)
#else
#define dprintf(format, ...) (void) 0
#endif

#define error(format, ...) do {			\
    fprintf(stderr, format, ## __VA_ARGS__);	\
    exit(0);					\
  } while(0)


int plop = 0;


int main(int argc, char**argv) {
  int fd = shm_open("/key", O_CREAT| O_RDWR, 0666);
  if(fd<0) {
    error("shm_open failed");
  }

  /* set the size of the shared memory segment */
  if(ftruncate(fd, 8192) < 0) {
    error("ftruncate failed");
  }

  if(fork() == 0 ) {
    dprintf("[%d] I'm the child process\n", getpid());
/* map the shared memory segment in the current address space */
    void* buffer = NULL;
    if((buffer = mmap((void*)0x20000000, 8192, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) <0) {
      error("mmap failed");
    }

    dprintf("child process starts working\n");
    sleep(5);
    dprintf("child process stops working\n");
    int* ptr = buffer;
    *ptr = 1;

    int* ptr2 = ptr + 1;
    dprintf("child process starts waiting\n");
    while(*ptr2 == 0) { /* do nothing */ }
    dprintf("child process stops waiting\n");
    
    /* unmap the memory region */
    if(munmap(buffer, 8192) < 0) {
      error("munmap failed");
    }
    /* close the shared memory segment */
    if(close(fd) < 0){
      error("close failed");
    }    
  } else {
    dprintf("[%d] I'm the parent process\n", getpid());

    /* map the shared memory segment in the current address space */
    void* buffer = NULL;
    if((buffer = mmap((void*)0x10000000, 8192, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) <0) {
      error("mmap failed");
    }

    int* ptr = buffer;
    dprintf("parent process starts waiting\n");
    while(*ptr == 0) { /* do nothing */ }
    dprintf("parent process stops waiting\n");

    sleep(5);
    dprintf("parent process notifies the child process\n");
    int* ptr2 = ptr + 1;
    *ptr2 = 1;    
    
    /* unmap the memory region */
    if(munmap(buffer, 8192) < 0) {
      error("munmap failed");
    }
    /* close the shared memory segment */
    if(close(fd) < 0){
      error("close failed");
    }
    
  }
  int retval = shm_unlink(/key);
  if(retval<0) {
    error("shm_unlink failed");
  }

  
  return EXIT_SUCCESS;
}