WScrollPanePeer.initialize has the following statements:

        super.initialize();
        setInsets();
        Insets i = getInsets();
        setScrollPosition(-i.left,-i.top);

Here both setInsets and setScrollPosition are native methods, both need to be run on the toolkit thread. These two calls can be coalesced so that both tasks are performed in a single JNI call with a single switch to the toolkit thread.