code: def start(self):
      if self._started:
          return
  
      self._started = True
      self._th_collector.start()
  
imports: import datetime
  import logging
  import time
  import weakref
  from collections import Counter
  from threading import Thread
  from typing import Union
  import aim.ext.transport.proto.remote_router_pb2
label_desc: Use image node_id 2 for calling the RPCHeartbeatSender obj's underlying member method code with example usage: obj.start() without return types