[jira] [Created] (TINKERPOP-1519) TinkerGraphComputer doesn't handle multiple MessageScopes in single iteration

["Felix Chapman (JIRA)" <ji...@apache.org>]

Felix Chapman created TINKERPOP-1519:
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             Summary: TinkerGraphComputer doesn't handle multiple MessageScopes in single iteration
                 Key: TINKERPOP-1519
                 URL: https://issues.apache.org/jira/browse/TINKERPOP-1519
             Project: TinkerPop
          Issue Type: Bug
          Components: tinkergraph
    Affects Versions: 3.1.1-incubating
         Environment: Mac OSX
            Reporter: Felix Chapman
            Priority: Minor


When executing a VertexProgram that sends messages on multiple MessageScopes in a single iteration, then the messages behave as if they were sent on all scopes within that iteration.

The problem can be resolved by using only a single MessageScope per iteration, but this involves increasing the number of iterations.

An example of this behaviour is below:

{{
public class TinkerTest {

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        TinkerGraph graph = TinkerGraph.open();
        Vertex a = graph.addVertex("a");
        Vertex b = graph.addVertex("b");
        Vertex c = graph.addVertex("c");
        a.addEdge("edge", b);
        b.addEdge("edge", c);

        // Simple graph:
        // a -> b -> c

        // Execute a traversal program that sends an incoming message of "2" and an outgoing message of "1" from "b"
        // then each vertex sums any received messages
        ComputerResult result = graph.compute().program(new MyVertexProgram()).submit().get();

        // We expect the results to be {a=2, b=0, c=1}. Instead it is {a=3, b=0, c=3}
        System.out.println(result.graph().traversal().V().group().by(Element::label).by("count").next());
    }
}

class MyVertexProgram implements VertexProgram<Long> {

    private final MessageScope.Local<Long> countMessageScopeIn = MessageScope.Local.of(__::inE);
    private final MessageScope.Local<Long> countMessageScopeOut = MessageScope.Local.of(__::outE);

    private static final String MEMORY_KEY = "count";

    private static final Set<String> COMPUTE_KEYS = Collections.singleton(MEMORY_KEY);

    @Override
    public void setup(final Memory memory) {}

    @Override
    public GraphComputer.Persist getPreferredPersist() {
        return GraphComputer.Persist.VERTEX_PROPERTIES;
    }

    @Override
    public Set<String> getElementComputeKeys() {
        return COMPUTE_KEYS;
    }

    @Override
    public Set<MessageScope> getMessageScopes(final Memory memory) {
        return Sets.newHashSet(countMessageScopeIn, countMessageScopeOut);
    }

    @Override
    public void execute(Vertex vertex, Messenger<Long> messenger, Memory memory) {
        switch (memory.getIteration()) {
            case 0:
                if (vertex.label().equals("b")) {
                    messenger.sendMessage(this.countMessageScopeIn, 2L);
                    messenger.sendMessage(this.countMessageScopeOut, 1L);
                }
                break;
            case 1:
                long edgeCount = IteratorUtils.reduce(messenger.receiveMessages(), 0L, (a, b) -> a + b);
                vertex.property(MEMORY_KEY, edgeCount);
                break;
        }
    }

    @Override
    public boolean terminate(final Memory memory) {
        return memory.getIteration() == 1;
    }

    @Override
    public GraphComputer.ResultGraph getPreferredResultGraph() {
        return GraphComputer.ResultGraph.NEW;
    }

    @Override
    public MyVertexProgram clone() {
        try {
            return (MyVertexProgram) super.clone();
        } catch (final CloneNotSupportedException e) {
            throw new RuntimeException(e);
        }
    }

}
}}



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