code: def _worker(self):
      while True:
          sleep(0.001)
          cache_file_name = self._q.get()
          self._current_data = {}
          if cache_file_name is None:
              self._q.task_done()
              break
          self._current_data = self.read_cache(
              cache_file_name, self._variables
          )
          self._q.task_done()
  
imports: import atexit
  import csv
  import os
  import threading
  from collections import OrderedDict, deque
  from time import sleep
  import numpy
  from nnabla.config import nnabla_config
  from nnabla.logger import logger
  from nnabla.utils.communicator_util import current_communicator
  from six.moves import queue
  from .data_source import DataSource
  from .data_source_loader import FileReader, load
label_desc: Use image node_id 3 for calling the CachePrefetcher obj's underlying member method code with example usage: obj._worker() without return types