code: public void addMaybeStartHandler(Handler handler, Stage stage) throws Exception
    {
      synchronized (handlers) {
        if (started.get()) {
          if (currStage == null || stage.compareTo(currStage) < 1) {
            handler.start();
          }
        }
        handlers.get(stage).add(handler);
      }
    }
docs: Adds a handler to the Lifecycle and starts it if the lifecycle has already been started.
  
  @param handler The hander to add to the lifecycle
  @param stage   The stage to add the lifecycle at
  
  @throws Exception an exception thrown from handler.start().  If an exception is thrown, the handler is *not* added