* @lucene.internal */
  public synchronized void decRefDeleter(SegmentInfos segmentInfos) throws IOException {
    ensureOpen();
    deleter.decRef(segmentInfos);
    if (infoStream.isEnabled("IW")) {
      infoStream.message("IW", "decRefDeleter for NRT reader version=" + segmentInfos.getVersion() + " segments=" + segString(segmentInfos));
    }
  }