public void addEdge(Dependency dependency) {
    if (!edges.contains(dependency)) {
      edges.add(dependency);
      Set<Dependency> outboundEdges = vertices.get(dependency.getDepender());
      if (outboundEdges == null) {
        outboundEdges = new HashSet();
        vertices.put(dependency.getDepender(), outboundEdges);
      }
      outboundEdges.add(dependency);

      if (vertices.get(dependency.getDependsOn()) == null) {
        vertices.put(dependency.getDependsOn(), new HashSet());
      }
    }
  }
Add an edge to the dependency graph.
geode-core/src/main/java/org/apache/geode/distributed/internal/deadlock/DependencyGraph.java