code: func SetupSignalHandler() (stopCh <-chan struct{}) {
  	close(onlyOneSignalHandler) // panics when called twice
  
  	stop := make(chan struct{})
  	c := make(chan os.Signal, 2)
  	signal.Notify(c, shutdownSignals...)
  	go func() {
  		<-c
  		close(stop)
  		<-c
  		os.Exit(1) // second signal. Exit directly.
  	}()
  
  	return stop
  }
docs: // SetupSignalHandler registered for SIGTERM and SIGINT. A stop channel is returned
  // which is closed on one of these signals. If a second signal is caught, the program
  // is terminated with exit code 1.