code: def _decref_writing_key(self, session_id: str, data_key: str):
      self._writing_infos[(session_id, data_key)].ref_counts -= 1
      if self._writing_infos[(session_id, data_key)].ref_counts == 0:
          del self._writing_infos[(session_id, data_key)]
  
file_path: mars/mars/services/storage/transfer.py
imports: import asyncio
  import logging
  from dataclasses import dataclass
  from typing import Dict, List
  from ...None import oscar
  from ...lib.aio import alru_cache
  from ...storage import StorageLevel
  from ...utils import dataslots
  from .core import DataManagerActor, WrappedStorageFileObject
  from .handler import StorageHandlerActor
label_desc: Use image node_id 3 for calling the ReceiverManagerActor obj's underlying member method code with example usage: obj._decref_writing_key(session_id, data_key) without return types