#include <stdio.h>
#include <stdlib.h>
#include <mach/mach_init.h>
#include <mach/mach_error.h>
#include <mach/semaphore.h>
#include <mach/task.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h> 
#include <fcntl.h>
#include <unistd.h>

#define FILE_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)

/* global */
semaphore_t mutex;

int main() {
  int fd, i, nloop, zero = 0;
  int *ptr = NULL;
  nloop = 50000;

  fd = open("./share", O_RDWR | O_CREAT, FILE_MODE);
  write(fd, &zero, sizeof(int));
  ptr = mmap(NULL, sizeof(int), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  close(fd);

  printf("ready mmap: %d\n", getpid());

  mach_port_t self = mach_task_self();
  kern_return_t ret = semaphore_create(self, &mutex, SYNC_POLICY_FIFO, 1);
  if (ret != KERN_SUCCESS) {
    fprintf(stderr, "semaphore create failed. Error <%d, %s>", ret, mach_error_string(ret));
    return ret;
  }

  setbuf(stdout, NULL);

  /* child */
  if (fork() == 0) {
    for (i = 0; i < nloop; i++) {
      ret = semaphore_wait(mutex);
      (*ptr)++;
      (*ptr)--;
      (*ptr)++;
      printf("child (%d): %d\n", getpid(), *ptr);
      ret = semaphore_signal(mutex);
    }
    exit(0);
  } else {
    /* parent */
    for (i = 0; i < nloop; i++) {
      ret = semaphore_wait(mutex);
      (*ptr)++;
      (*ptr)--;
      (*ptr)++;
      printf("parent (%d): %d\n", getpid(), *ptr);
      ret = semaphore_signal(mutex);
    }
  }

  return 0;
}