Fix issue with weighted graphs

Co-authored-by: Ioannis Panagiotas <ioannis.panagiotas@neotechnology.com>

Author: vnickolov

algo/src/main/java/org/neo4j/gds/leiden/Leiden.java

@@ -151,7 +151,7 @@ private void initVolumes(HugeDoubleArray nodeVolumes, HugeDoubleArray communityV
                 rootGraph.nodeCount(),
                 concurrency,
                 nodeId -> {
-                    rootGraph.forEachRelationship(nodeId, 1.0, (s, t, w) -> {
+                    rootGraph.concurrentCopy().forEachRelationship(nodeId, 1.0, (s, t, w) -> {
                         nodeVolumes.addTo(nodeId, w);
                         communityVolumes.addTo(nodeId, w);
                         return true;

algo/src/test/java/org/neo4j/gds/leiden/LeidenWeightedTest.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) "Neo4j"
+ * Neo4j Sweden AB [http://neo4j.com]
+ *
+ * This file is part of Neo4j.
+ *
+ * Neo4j is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.neo4j.gds.leiden;
+
+import org.junit.jupiter.api.RepeatedTest;
+import org.neo4j.gds.Orientation;
+import org.neo4j.gds.core.utils.progress.tasks.ProgressTracker;
+import org.neo4j.gds.extension.GdlExtension;
+import org.neo4j.gds.extension.GdlGraph;
+import org.neo4j.gds.extension.IdFunction;
+import org.neo4j.gds.extension.Inject;
+import org.neo4j.gds.extension.TestGraph;
+
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@GdlExtension
+class LeidenWeightedTest {
+
+    @GdlGraph(orientation = Orientation.UNDIRECTED)
+    private static final String DB_CYPHER =
+        "CREATE" +
+        "  (nAlice:User)," +
+        "  (nBridget:User)," +
+        "  (nCharles:User)," +
+        "  (nDoug:User)," +
+        "  (nMark:User)," +
+        "  (nMichael:User)," +
+
+        "  (nAlice)-[:LINK {weight: 1}]->(nBridget)," +
+        "  (nAlice)-[:LINK {weight: 1}]->(nCharles)," +
+        "  (nCharles)-[:LINK {weight: 1}]->(nBridget)," +
+
+        "  (nAlice)-[:LINK {weight: 5}]->(nDoug)," +
+
+        "  (nMark)-[:LINK {weight: 1}]->(nDoug)," +
+        "  (nMark)-[:LINK {weight: 1}]->(nMichael)," +
+        "  (nMichael)-[:LINK {weight: 1}]->(nMark)";
+
+    @Inject
+    private TestGraph graph;
+
+    @Inject
+    private IdFunction idFunction;
+
+    @RepeatedTest(10)
+    void weightedLeiden() {
+        var maxLevels = 10;
+        Leiden leiden = new Leiden(
+            graph,
+            maxLevels,
+            1.0 / graph.relationshipCount(),
+            0.01,
+            19L,
+            4,
+            ProgressTracker.NULL_TRACKER
+        );
+
+        var leidenResult = leiden.compute();
+
+        assertThat(leidenResult.ranLevels()).isLessThanOrEqualTo(maxLevels);
+        assertThat(leidenResult.didConverge()).isTrue();
+
+        var communities = leidenResult.communities();
+
+        var communitiesMap = Stream.of("nAlice", "nBridget", "nCharles", "nDoug", "nMark", "nMichael")
+            .collect(Collectors.groupingBy(v -> communities.get(idFunction.of(v))));
+
+        assertThat(communitiesMap.values())
+            .satisfiesExactlyInAnyOrder(
+                community -> assertThat(community).containsExactlyInAnyOrder("nAlice", "nDoug"),
+                community -> assertThat(community).containsExactlyInAnyOrder("nBridget", "nCharles"),
+                community -> assertThat(community).containsExactlyInAnyOrder("nMark", "nMichael")
+            );
+
+    }
+}