code: @Override
    protected boolean requestInvoke(FrameBuffer frameBuffer) {
      Runnable invocation = getRunnable(frameBuffer);
      if (invoker != null) {
        try {
          invoker.execute(invocation);
          return true;
        } catch (RejectedExecutionException rx) {
          LOGGER.warn("ExecutorService rejected execution!", rx);
          return false;
        }
      } else {
        // Invoke on the caller's thread
        invocation.run();
        return true;
      }
    }
docs: We override the standard invoke method here to queue the invocation for
  invoker service instead of immediately invoking. If there is no thread
  pool, handle the invocation inline on this thread