// build it as gcc -std=c99 aio_race.c -o aio_race -lpthread -laio

#define _GNU_SOURCE

#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <assert.h>
#include <unistd.h>
#include <string.h>
#include <libaio.h>
#include <stdbool.h>

#define PAGE_SIZE 4096

#define FILENAME "tempfile"
#define FILEPATTERN '1'
#define DESTROY_PATTERN '2'

#define THREADS_NUM 100

void remove_tempfile(void) {
  assert(!unlink(FILENAME));
}

void aio_worker(void *ptr) {
  int fd = open(FILENAME, O_DIRECT | O_RDONLY);
  char buffer[PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));

  while(true) {
    io_context_t ctx;
    struct iocb cb;
    struct iocb *cbs[1];

    assert(!io_queue_init(1, &ctx));
    io_prep_pread(&cb, fd, buffer, PAGE_SIZE, 0);
    cbs[0] = &cb;

    memset(buffer, '0', PAGE_SIZE);
    assert(io_submit(ctx, 1, &cbs[0]) == 1);
    // wait random time (0-500ms) ?

    io_destroy(ctx);
    memset(buffer, DESTROY_PATTERN, PAGE_SIZE);
    // wait random for (0-500ms) ?

    // check it is still DESTROY_PATTERN
    for (int i = 0; i < PAGE_SIZE; i++) {
      if (buffer[i] != DESTROY_PATTERN) {
        fprintf(stderr, "Buffer has unexpected character: %c\n", buffer[i]);
        exit(EXIT_FAILURE);
      }
    }
  }

  close(fd);
}

int main(void) {
  int fd = open(FILENAME, O_CREAT | O_TRUNC | O_APPEND | O_RDWR, S_IRUSR | S_IWUSR);
  assert(fd != -1);
  //atexit(remove_tempfile);

  char buffer[PAGE_SIZE];
  memset(buffer, FILEPATTERN, PAGE_SIZE);
  write(fd, buffer, PAGE_SIZE);
  close(fd);

  pthread_t threads[THREADS_NUM];
  for (int i = 0; i < THREADS_NUM; i++) {
    assert(!pthread_create(&threads[i], NULL, (void *)&aio_worker, NULL));
  }
  for (int i = 0; i < THREADS_NUM; i++) {
    assert(!pthread_join(threads[i], NULL));
  }

  return EXIT_SUCCESS;
}