code: public void refresh() throws IOException {
      updateLock.writeLock().lock();
      try {
        root = new InnerDesc(fs, fs.getFileStatus(path),
          new MinFileFilter(conf.getLong(GRIDMIX_MIN_FILE, 128 * 1024 * 1024),
                            conf.getLong(GRIDMIX_MAX_TOTAL, 100L * (1L << 40))));
        if (0 == root.getSize()) {
          throw new IOException("Found no satisfactory file in " + path);
        }
      } finally {
        updateLock.writeLock().unlock();
      }
    }
docs: (Re)generate cache of input FileStatus objects.