class_docstr: Get data from file cache directly.
code: def initialize_cache_files(self, filename):
      length = -1
      with self._filereader.open_cache(filename) as cache:
          # Check variables.
          if self._variables is None:
              self._variables = list(cache.keys())
          else:
              if current_communicator():
                  if not set(self._variables) == set(cache.keys()):
                      logger.log(
                          99,
                          "Error at worker {} {} {}".format(
                              current_communicator().rank,
                              set(self._variables),
                              set(cache.keys()),
                          ),
                      )
                      raise
  
          for k, v in cache.items():
              if length < 0:
                  length = len(v)
              else:
                  assert length == len(v)
          self._cache_files.append((filename, length))
          logger.info("{} {}".format(filename, length))
          if length > self._max_length:
              self._max_length = length
  
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 CacheDataSource obj's underlying member method code with example usage: obj.initialize_cache_files(filename) without return types