Review

class IndexWriter {
  /** Expert: like {@link #getReader}, except you can
   *  specify which termInfosIndexDivisor should be used for
   *  any newly opened readers.
   * @param termInfosIndexDivisor Subsamples which indexed
   *  terms are loaded into RAM. This has the same effect as {@link
   *  IndexWriter#setTermIndexInterval} except that setting
   *  must be done at indexing time while this setting can be
   *  set per reader.  When set to N, then one in every
   *  N*termIndexInterval terms in the index is loaded into
   *  memory.  By setting this to a value > 1 you can reduce
   *  memory usage, at the expense of higher latency when
   *  loading a TermInfo.  The default value is 1.  Set this
   *  to -1 to skip loading the terms index entirely. */
  public IndexReader getReader(int termInfosIndexDivisor) throws IOException {
    if (infoStream != null) {
      message("flush at getReader");
    }

    // Do this up front before flushing so that the readers
    // obtained during this flush are pooled, the first time
    // this method is called:
    poolReaders = true;

    flush(true, true, true);
    
    // Prevent segmentInfos from changing while opening the
    // reader; in theory we could do similar retry logic,
    // just like we do when loading segments_N
    synchronized(this) {
      return new ReadOnlyDirectoryReader(this, segmentInfos, termInfosIndexDivisor);
    }
  }

}