code: def close(self):
      if not self._closed:
          self._closed = True
          self._q_cmd.put("stop")
          assert self._q_cmd_out.get(), "Failed to stop process"
          self._p.join()
  
imports: from collections import OrderedDict
  import multiprocessing
  import os
  from queue import Empty
  from typing import Any, Callable, Dict, List, Optional, Set, Tuple, Union
  from typing_extensions import TypedDict
  from ...dataset import DistributedDataset
  from ...tokenizers import CPMBeeTokenizer
  from ...utils.config import load_dataset_config
  import numpy
  import time
  from numpy.typing import NDArray
  import torch
  import bmtrain
  import importlib.machinery
  import importlib.util
  import types
  import random
label_desc: Use image node_id 2 for calling the MixedDataset obj's underlying member method code with example usage: obj.close() without return types