class_docstr: Router provides mapping from external address to internal address.
code: def add_router(self, router: "Router"):
      self._curr_external_addresses.extend(
          router._curr_external_addresses
      )
      self._local_mapping.update(router._local_mapping)
      self._mapping.update(router._mapping)
      self._cache_local = threading.local()
  
file_path: mars/mars/oscar/backends/router.py
imports: import threading
  from typing import Dict, List, Tuple, Type, Any, Optional
  from .communication import get_client_type, Client
label_desc: Use image node_id 7 for calling the Router obj's underlying member method code with example usage: obj.add_router(router) without return types