code: def _fill_cache(self, idx):
      feat_file = self.annotation_db[idx]["feature_path"]
      features, info = self._read_features_and_info(feat_file)
      self.feature_dict[feat_file] = (features, info)
  
file_path: mmf/mmf/datasets/databases/features_database.py
imports: import logging
  from multiprocessing.pool import ThreadPool
  import tqdm
  from mmf.datasets.databases.image_database import ImageDatabase
  from mmf.datasets.databases.readers.feature_readers import FeatureReader
  from mmf.utils.distributed import is_main
  from mmf.utils.general import get_absolute_path
label_desc: Use image node_id 3 for calling the FeaturesDatabase obj's underlying member method code with example usage: obj._fill_cache(idx) without return types