class_docstr: Router provides mapping from external address to internal address.
code: def set_instance(router: Optional["Router"]):
      # Default router is set when an actor pool started
      Router._instance = router
  
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 1 for calling the Router obj's underlying member method code with example usage: obj.set_instance(router) without return types