code: public static void init(RythmEngine engine) {
          if (null != _Rythm.engine) throw new IllegalStateException("Rythm is already initialized");
          _Rythm.engine = engine;
          engine.setShutdownListener(new RythmEngine.IShutdownListener() {
              @Override
              public void onShutdown() {
                  _Rythm.engine = null;
              }
          });
      }
docs: Use an pre-initialized engine as the default engine. Note if there are already default
  engine initialized then the method will raise a <code>IllegalStateException</code>
  <p/>
  <p>When the default engine's {@link org.rythmengine.RythmEngine#shutdown() shutdown} method get called
  the default engine instance will be discard. Calling any servicing method of
  <code>Rythm</code> will cause an new <code>RythmEngine</code> initialized as
  the new default engine</p>
  
  @param engine