code: public void awaitError(def<Void> handler) {
                  while (!container.inProcess) {
                          // block
                          Style.sleep(1);
                  }
                  synchronized (container) {
                          if (null != throwable) {
                                  handler.apply(Style.$(throwable));
                          }
                  }
          }
docs: Handle exceptions that async task thrown.<br>
  the method would block current thread until async task finished or
  thrown with an exception, the handling process would be taken in
  current thread.<br>
  
  @param handler a function to invoke when occurred an exception<br>
  for all Throwable caught from the async task would be
  packed into StyleRuntimeException
  @see StyleRuntimeException