code: BlockInfo[] getTimedOutBlocks() {
      synchronized (timedOutItems) {
        if (timedOutItems.size() <= 0) {
          return null;
        }
        BlockInfo[] blockList = timedOutItems.toArray(
                                new BlockInfo[timedOutItems.size()]);
        timedOutItems.clear();
        return blockList;
      }
    }
docs: Returns a list of blocks that have timed out their
  replication requests. Returns null if no blocks have
  timed out.