code: func (el *CallbackEventListener) RegAccountShutdown(f SignalEventCallback) {
  	el.ids = append(el.ids, el.em.RegisterListener(func(data interface{}) {
  		f()
  	}, event.EventShutdown))
  }
docs: // RegAccountShutdown registers this listener to listen for shutdown messages.
  // A shutdown signal is normally only signaled once by the account on it's graceful termination.