* @lucene.internal */
  synchronized String segString(Iterable<SegmentCommitInfo> infos) {
    final StringBuilder buffer = new StringBuilder();
    for(final SegmentCommitInfo info : infos) {
      if (buffer.length() > 0) {
        buffer.append(' ');
      }
      buffer.append(segString(info));
    }
    return buffer.toString();
  }