realized that StreamFactory.parallelStream(g.V()) was not sufficient for parallization. When doing it over the raw Map<Object,Vertex>.values().parallelStream() ... things in TinkerGraph went hay-wire. I got MapReduce implementation to be thread-safe, but need to get VertexProgram execute thread-safe for TinkerGraph... TinkerGraphView is the culprit. Got tired. Will fix later.