#include <sys/mman.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <iostream>

#include <bits/atomicity.h>
using __gnu_cxx::__atomic_add;
using __gnu_cxx::__exchange_and_add;
using namespace std;

void die(char *msg) {
  perror(msg);
  exit(0);
}

void add(volatile _Atomic_word *to, int amt) {
  __atomic_add(to, amt);
}

int main(int argc, char *argv[]) {
  if (argc < 2) {
    die("bad usage");
  }
  int mmap_fd = open(argv[1], O_RDWR);
  if (mmap_fd < 0)
    die("couldn't open mmap");
  void *mem = mmap(NULL, sizeof(_Atomic_word), PROT_WRITE, MAP_SHARED, mmap_fd, 0);
  if (mem == NULL)
    die("couldn't mmap file");
  volatile _Atomic_word *counter = (volatile _Atomic_word *)mem;

  int count = atoi(argv[2]);
  for(int i=0;i<count;i++) {
    add(counter, 1);
  }
  cout << "counter is now " << *counter << endl;
}