code: private ServerSocket initializeServer(CoronaConf conf) throws IOException {
      // Choose any free port.
      ServerSocket sessionServerSocket =
        new ServerSocket(0, 0, getLocalAddress());
      TServerSocket tServerSocket = new TServerSocket(sessionServerSocket,
                                                      conf.getCMSoTimeout());
  
      TFactoryBasedThreadPoolServer.Args args =
        new TFactoryBasedThreadPoolServer.Args(tServerSocket);
      args.processor(new SessionDriverServiceProcessor(incoming));
      args.transportFactory(new TTransportFactory());
      args.protocolFactory(new TBinaryProtocol.Factory(true, true));
      args.stopTimeoutVal = 0;
      server = new TFactoryBasedThreadPoolServer(
        args, new TFactoryBasedThreadPoolServer.DaemonThreadFactory());
      return sessionServerSocket;
    }
docs: Start the SessionDriver callback server
  @param conf the corona configuration for this session
  @return the server socket of the callback server
  @throws IOException