code: public void sessionIdle(IoSession session, IdleStatus status)
              throws Exception {
          SingleSessionIoHandler handler = (SingleSessionIoHandler) session
                  .getAttribute(HANDLER);
          handler.sessionIdle(status);
      }
docs: Delegates the method call to the
  {@link SingleSessionIoHandler#sessionIdle(IdleStatus)} method of the
  handler assigned to this session.