code: private static void writeFile(CyclicBarrier barrier, AtomicLong runtime, int count,
        AlluxioConfiguration alluxioConf)
        throws Exception {
      FileSystem fileSystem = FileSystem.Factory.create(alluxioConf);
      byte[] buffer = new byte[(int) Math.min(sFileSize, 4 * Constants.MB)];
      Arrays.fill(buffer, (byte) 'a');
      AlluxioURI path = filename(count);
  
      if (fileSystem.exists(path)) {
        fileSystem.delete(path);
      }
  
      barrier.await();
      long startTime = System.nanoTime();
      long bytesWritten = 0;
      try (FileOutStream outStream = fileSystem.createFile(path)) {
        while (bytesWritten < sFileSize) {
          outStream.write(buffer, 0, (int) Math.min(buffer.length, sFileSize - bytesWritten));
          bytesWritten += buffer.length;
        }
      }
      runtime.addAndGet(System.nanoTime() - startTime);
    }
docs: Writes a file.
  
  @param count the count to determine the filename
  @throws Exception if it fails to write