code: private void initBlkLocInfoExpireMap(long expireTime) {
      if (blkLocInfoExpireTimeout < 0) {
        return;
      }
  
      this.blkLocInfoExpireMap = new HashMap<LocatedBlock, Long>(this
          .getLocatedBlocks().size());
      for (LocatedBlock lb : this.getLocatedBlocks()) {
        blkLocInfoExpireMap.put(lb, expireTime);
      }
      timeBlkLocInfoExpire = expireTime;
    }
docs: Initial the blockExpireMap, which keeps track of the expiration time of all
  block location info.
  
  @param expireTime
  time for the located block to expire