public List<LocalVertex> findSinkModuleVertices() {
        ArrayList<LocalVertex> ret = new ArrayList<>();
        Iterator<LocalVertex> iter = graph.iteratorOfVertex();
        while (iter.hasNext()) {
            LocalVertex vertex = iter.next();
            if (!(vertex instanceof LocalPhysicalVertex))
                continue;

            LocalPhysicalVertex lpv = (LocalPhysicalVertex) vertex;
            if (lpv.getVertex().isSinkModule())
                ret.add(lpv);
        }
        return ret;
    }