code: public void releaseAllChunkMemoryUsage()
    {
      if (chunks == null || chunks.size() == 0)
      {
        return;
      }
  
      for (int i = 0; i < chunks.size(); i++)
      {
        releaseCurrentMemoryUsage(i, chunks.get(i).computeNeededChunkMemory());
      }
    }
docs: release all existing chunk memory usage before close