public synchronized void drop(SegmentCommitInfo info) throws IOException {
      final ReadersAndUpdates rld = readerMap.get(info);
      if (rld != null) {
        assert info == rld.info;
//        System.out.println("[" + Thread.currentThread().getName() + "] ReaderPool.drop: " + info);
        readerMap.remove(info);
        rld.dropReaders();
      }
    }