}
  }

  enum Impl {
    NEW {
      @Override
      <T> Facade<T> newFacade() {
        return new NewAbstractFutureFacade<T>();
      }
    },
    OLD {
      @Override
      <T> Facade<T> newFacade() {
        return new OldAbstractFutureFacade<T>();
      }
    };

    abstract <T> Facade<T> newFacade();
  }

  @SuppressWarnings("ThreadPriorityCheck") // TODO: b/175898629 - Consider onSpinWait.