func (g *Graph) getOrCreateVertex_locked(vertexType vertexType, namespace, name string) *namedVertex {
	if vertex, exists := g.getVertex_rlocked(vertexType, namespace, name); exists {
		return vertex
	}
	return g.createVertex_locked(vertexType, namespace, name)
}

// must be called under a read lock
func (g *Graph) getVertex_rlocked(vertexType vertexType, namespace, name string) (*namedVertex, bool) {

	r.graph.lock.RLock()
	defer r.graph.lock.RUnlock()

	nodeVertex, exists := r.graph.getVertex_rlocked(nodeVertexType, "", nodeName)
	if !exists {
		return false, fmt.Errorf("unknown node '%s' cannot get %s %s/%s", nodeName, vertexTypes[startingType], startingNamespace, startingName)
	}

	startingVertex, exists := r.graph.getVertex_rlocked(startingType, startingNamespace, startingName)
	if !exists {