code: public long getInputFiles(long minSize, Collection<FileStatus> files)
        throws IOException {
      updateLock.readLock().lock();
      try {
        return root.selectFiles(minSize, files);
      } finally {
        updateLock.readLock().unlock();
      }
    }
docs: Gather a collection of files at least as large as minSize.
  @return The total size of files returned.