code: def _create_master(self, port, exit_event):
      master = Master(port=port)
      th = threading.Thread(target=master.run)
      th.start()
  
      exit_event.wait()
      master.exit()
      th.join()
  
imports: import unittest
  import parl
  import time
  import threading
  import multiprocessing
  from parl.remote.master import Master
  from parl.remote.worker import Worker
  from parl.remote.client import disconnect
  from parl.utils import get_free_tcp_port, _IS_WINDOWS
label_desc: Use image node_id 4 for calling the TestCluster obj's underlying member method code with example usage: obj._create_master(port, exit_event) without return types