/**
  * * Get sorted fileIds of the files cached in the worker.
  *
  * @return a sorted fileId list
  */
 private List<Long> getSortedFileIds() {
   Set<Long> fileIds = new HashSet<Long>();
   BlockStoreMeta storeMeta = mBlockDataManager.getStoreMeta();
   for (List<Long> blockIds : storeMeta.getBlockList().values()) {
     for (long blockId : blockIds) {
       long fileId =
           BlockId.createBlockId(BlockId.getContainerId(blockId), BlockId.getMaxSequenceNumber());
       fileIds.add(fileId);
     }
   }
   List<Long> sortedFileIds = new ArrayList<Long>(fileIds);
   Collections.sort(sortedFileIds);
   return sortedFileIds;
 }