@Override
    public void modifiedRegionUpdated(final long startOffsetInFile,
                                      final int length) {
      do {//CAS loop:
        final long actualFileSize = actualSize.get();
        final long requiredFileSize = startOffsetInFile + length;
        if (actualFileSize >= requiredFileSize) {
          return;
        }
        if (actualSize.compareAndSet(actualFileSize, requiredFileSize)) {
          return;
        }
      }
      while (true);
    }
@Override
    public void modifiedRegionUpdated(final long startOffsetInFile,
                                      final int length)