core/common/src/test/java/org/onosproject/store/trivial/DefaultTopology.java - onos - Gitiles

 /*
  * Copyright 2014-2015 Open Networking Laboratory
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 package org.onosproject.store.trivial;

 import static com.google.common.base.MoreObjects.toStringHelper;
 import static org.onlab.graph.GraphPathSearch.ALL_PATHS;
 import static org.onosproject.core.CoreService.CORE_PROVIDER_ID;
 import static org.onosproject.net.Link.State.ACTIVE;
 import static org.onosproject.net.Link.State.INACTIVE;
 import static org.onosproject.net.Link.Type.INDIRECT;

 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;

 import org.onlab.graph.DijkstraGraphSearch;
 import org.onlab.graph.GraphPathSearch;
 import org.onlab.graph.GraphPathSearch.Result;
 import org.onlab.graph.TarjanGraphSearch;
 import org.onlab.graph.TarjanGraphSearch.SCCResult;
 import org.onosproject.net.AbstractModel;
 import org.onosproject.net.ConnectPoint;
 import org.onosproject.net.DefaultPath;
 import org.onosproject.net.DeviceId;
 import org.onosproject.net.Link;
 import org.onosproject.net.Path;
 import org.onosproject.net.provider.ProviderId;
 import org.onosproject.net.topology.ClusterId;
 import org.onosproject.net.topology.DefaultTopologyCluster;
 import org.onosproject.net.topology.DefaultTopologyVertex;
 import org.onosproject.net.topology.GraphDescription;
 import org.onosproject.net.topology.LinkWeight;
 import org.onosproject.net.topology.Topology;
 import org.onosproject.net.topology.TopologyCluster;
 import org.onosproject.net.topology.TopologyEdge;
 import org.onosproject.net.topology.TopologyGraph;
 import org.onosproject.net.topology.TopologyVertex;

 import com.google.common.base.Supplier;
 import com.google.common.base.Suppliers;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.ImmutableSetMultimap;
 import com.google.common.collect.ImmutableSetMultimap.Builder;

 // FIXME: Move to onos-core-common when ready
 /**
  * Default implementation of the topology descriptor. This carries the backing
  * topology data.
  */
 public class DefaultTopology extends AbstractModel implements Topology {

     private static final DijkstraGraphSearch<TopologyVertex, TopologyEdge> DIJKSTRA = new DijkstraGraphSearch<>();
     private static final TarjanGraphSearch<TopologyVertex, TopologyEdge> TARJAN = new TarjanGraphSearch<>();

     private final long time;
     private final long creationTime;
     private final long computeCost;
     private final TopologyGraph graph;

     private final LinkWeight weight;
     private final Supplier<SCCResult<TopologyVertex, TopologyEdge>> clusterResults;
     private final Supplier<ImmutableMap<ClusterId, TopologyCluster>> clusters;
     private final Supplier<ImmutableSet<ConnectPoint>> infrastructurePoints;
     private final Supplier<ImmutableSetMultimap<ClusterId, ConnectPoint>> broadcastSets;

     private final Supplier<ClusterIndexes> clusterIndexes;

     /**
      * Creates a topology descriptor attributed to the specified provider.
      *
      * @param providerId
      *            identity of the provider
      * @param description
      *            data describing the new topology
      */
     DefaultTopology(ProviderId providerId, GraphDescription description) {
         super(providerId);
         this.time = description.timestamp();
         this.creationTime = description.creationTime();

         // Build the graph
         this.graph = new DefaultTopologyGraph(description.vertexes(),
                 description.edges());

         this.clusterResults = Suppliers.memoize(() -> searchForClusters());
         this.clusters = Suppliers.memoize(() -> buildTopologyClusters());

         this.clusterIndexes = Suppliers.memoize(() -> buildIndexes());

         this.weight = new HopCountLinkWeight(graph.getVertexes().size());
         this.broadcastSets = Suppliers.memoize(() -> buildBroadcastSets());
         this.infrastructurePoints = Suppliers
                 .memoize(() -> findInfrastructurePoints());
         this.computeCost = Math.max(0, System.nanoTime() - time);
     }

     @Override
     public long time() {
         return time;
     }

     @Override
     public long creationTime() {
         return creationTime;
     }

     @Override
     public long computeCost() {
         return computeCost;
     }

     @Override
     public int clusterCount() {
         return clusters.get().size();
     }

     @Override
     public int deviceCount() {
         return graph.getVertexes().size();
     }

     @Override
     public int linkCount() {
         return graph.getEdges().size();
     }

     private ImmutableMap<DeviceId, TopologyCluster> clustersByDevice() {
         return clusterIndexes.get().clustersByDevice;
     }

     private ImmutableSetMultimap<TopologyCluster, DeviceId> devicesByCluster() {
         return clusterIndexes.get().devicesByCluster;
     }

     private ImmutableSetMultimap<TopologyCluster, Link> linksByCluster() {
         return clusterIndexes.get().linksByCluster;
     }

     /**
      * Returns the backing topology graph.
      *
      * @return topology graph
      */
     TopologyGraph getGraph() {
         return graph;
     }

     /**
      * Returns the set of topology clusters.
      *
      * @return set of clusters
      */
     Set<TopologyCluster> getClusters() {
         return ImmutableSet.copyOf(clusters.get().values());
     }

     /**
      * Returns the specified topology cluster.
      *
      * @param clusterId cluster identifier
      *
      * @return topology cluster
      */
     TopologyCluster getCluster(ClusterId clusterId) {
         return clusters.get().get(clusterId);
     }

     /**
      * Returns the topology cluster that contains the given device.
      *
      * @param deviceId device identifier
      *
      * @return topology cluster
      */
     TopologyCluster getCluster(DeviceId deviceId) {
         return clustersByDevice().get(deviceId);
     }

     /**
      * Returns the set of cluster devices.
      *
      * @param cluster topology cluster
      *
      * @return cluster devices
      */
     Set<DeviceId> getClusterDevices(TopologyCluster cluster) {
         return devicesByCluster().get(cluster);
     }

     /**
      * Returns the set of cluster links.
      *
      * @param cluster topology cluster
      *
      * @return cluster links
      */
     Set<Link> getClusterLinks(TopologyCluster cluster) {
         return linksByCluster().get(cluster);
     }

     /**
      * Indicates whether the given point is an infrastructure link end-point.
      *
      * @param connectPoint connection point
      *
      * @return true if infrastructure
      */
     boolean isInfrastructure(ConnectPoint connectPoint) {
         return infrastructurePoints.get().contains(connectPoint);
     }

     /**
      * Indicates whether the given point is part of a broadcast set.
      *
      * @param connectPoint connection point
      *
      * @return true if in broadcast set
      */
     boolean isBroadcastPoint(ConnectPoint connectPoint) {
         // Any non-infrastructure, i.e. edge points are assumed to be OK.
         if (!isInfrastructure(connectPoint)) {
             return true;
         }

         // Find the cluster to which the device belongs.
         TopologyCluster cluster = clustersByDevice().get(connectPoint.deviceId());
         if (cluster == null) {
             throw new IllegalArgumentException("No cluster found for device "
                     + connectPoint.deviceId());
         }

         // If the broadcast set is null or empty, or if the point explicitly
         // belongs to it, return true;
         Set<ConnectPoint> points = broadcastSets.get().get(cluster.id());
         return (points == null) || points.isEmpty() || points.contains(connectPoint);
     }

     /**
      * Returns the size of the cluster broadcast set.
      *
      * @param clusterId cluster identifier
      *
      * @return size of the cluster broadcast set
      */
     int broadcastSetSize(ClusterId clusterId) {
         return broadcastSets.get().get(clusterId).size();
     }

     /**
      * Returns the set of pre-computed shortest paths between source and
      * destination devices.
      *
      * @param src source device
      *
      * @param dst destination device
      *
      * @return set of shortest paths
      */
     Set<Path> getPaths(DeviceId src, DeviceId dst) {
         return getPaths(src, dst, null);
     }

     /**
      * Computes on-demand the set of shortest paths between source and
      * destination devices.
      *
      * @param src source device
      *
      * @param dst destination device
      *
      * @param weight link weight function
      *
      * @return set of shortest paths
      */
     Set<Path> getPaths(DeviceId src, DeviceId dst, LinkWeight weight) {
         final DefaultTopologyVertex srcV = new DefaultTopologyVertex(src);
         final DefaultTopologyVertex dstV = new DefaultTopologyVertex(dst);
         Set<TopologyVertex> vertices = graph.getVertexes();
         if (!vertices.contains(srcV) || !vertices.contains(dstV)) {
             // src or dst not part of the current graph
             return ImmutableSet.of();
         }

         GraphPathSearch.Result<TopologyVertex, TopologyEdge> result =
                 DIJKSTRA.search(graph, srcV, dstV, weight, ALL_PATHS);
         ImmutableSet.Builder<Path> builder = ImmutableSet.builder();
         for (org.onlab.graph.Path<TopologyVertex, TopologyEdge> path : result.paths()) {
             builder.add(networkPath(path));
         }
         return builder.build();
     }

     // Converts graph path to a network path with the same cost.
     private Path networkPath(org.onlab.graph.Path<TopologyVertex, TopologyEdge> path) {
         List<Link> links = new ArrayList<>();
         for (TopologyEdge edge : path.edges()) {
             links.add(edge.link());
         }
         return new DefaultPath(CORE_PROVIDER_ID, links, path.cost());
     }

     // Searches for SCC clusters in the network topology graph using Tarjan
     // algorithm.
     private SCCResult<TopologyVertex, TopologyEdge> searchForClusters() {
         return TARJAN.search(graph, new NoIndirectLinksWeight());
     }

     // Builds the topology clusters and returns the id-cluster bindings.
     private ImmutableMap<ClusterId, TopologyCluster> buildTopologyClusters() {
         ImmutableMap.Builder<ClusterId, TopologyCluster> clusterBuilder = ImmutableMap.builder();
         SCCResult<TopologyVertex, TopologyEdge> results = clusterResults.get();
         // Extract both vertexes and edges from the results; the lists form
         // pairs along the same index.
         List<Set<TopologyVertex>> clusterVertexes = results.clusterVertexes();
         List<Set<TopologyEdge>> clusterEdges = results.clusterEdges();

         // Scan over the lists and create a cluster from the results.
         for (int i = 0, n = results.clusterCount(); i < n; i++) {
             Set<TopologyVertex> vertexSet = clusterVertexes.get(i);
             Set<TopologyEdge> edgeSet = clusterEdges.get(i);

             ClusterId cid = ClusterId.clusterId(i);
             DefaultTopologyCluster cluster = new DefaultTopologyCluster(cid,
                                                                         vertexSet.size(),
                                                                         edgeSet.size(),
                                                                         findRoot(vertexSet));
             clusterBuilder.put(cid, cluster);
         }
         return clusterBuilder.build();
     }

     // Finds the vertex whose device id is the lexicographical minimum in the
     // specified set.
     private TopologyVertex findRoot(Set<TopologyVertex> vertexSet) {
         TopologyVertex minVertex = null;
         for (TopologyVertex vertex : vertexSet) {
             if ((minVertex == null) || (minVertex.deviceId().toString()
                     .compareTo(minVertex.deviceId().toString()) < 0)) {
                 minVertex = vertex;
             }
         }
         return minVertex;
     }

     // Processes a map of broadcast sets for each cluster.
     private ImmutableSetMultimap<ClusterId, ConnectPoint> buildBroadcastSets() {
         Builder<ClusterId, ConnectPoint> builder = ImmutableSetMultimap.builder();
         for (TopologyCluster cluster : clusters.get().values()) {
             addClusterBroadcastSet(cluster, builder);
         }
         return builder.build();
     }

     // Finds all broadcast points for the cluster. These are those connection
     // points which lie along the shortest paths between the cluster root and
     // all other devices within the cluster.
     private void addClusterBroadcastSet(TopologyCluster cluster, Builder<ClusterId, ConnectPoint> builder) {
         // Use the graph root search results to build the broadcast set.
         Result<TopologyVertex, TopologyEdge> result =
                 DIJKSTRA.search(graph, cluster.root(), null, weight, 1);
         for (Map.Entry<TopologyVertex, Set<TopologyEdge>> entry : result.parents().entrySet()) {
             TopologyVertex vertex = entry.getKey();

             // Ignore any parents that lead outside the cluster.
             if (clustersByDevice().get(vertex.deviceId()) != cluster) {
                 continue;
             }

             // Ignore any back-link sets that are empty.
             Set<TopologyEdge> parents = entry.getValue();
             if (parents.isEmpty()) {
                 continue;
             }

             // Use the first back-link source and destinations to add to the
             // broadcast set.
             Link link = parents.iterator().next().link();
             builder.put(cluster.id(), link.src());
             builder.put(cluster.id(), link.dst());
         }
     }

     // Collects and returns an set of all infrastructure link end-points.
     private ImmutableSet<ConnectPoint> findInfrastructurePoints() {
         ImmutableSet.Builder<ConnectPoint> builder = ImmutableSet.builder();
         for (TopologyEdge edge : graph.getEdges()) {
             builder.add(edge.link().src());
             builder.add(edge.link().dst());
         }
         return builder.build();
     }

     // Builds cluster-devices, cluster-links and device-cluster indexes.
     private ClusterIndexes buildIndexes() {
         // Prepare the index builders
         ImmutableMap.Builder<DeviceId, TopologyCluster> clusterBuilder =
                 ImmutableMap.builder();
         ImmutableSetMultimap.Builder<TopologyCluster, DeviceId> devicesBuilder =
                 ImmutableSetMultimap.builder();
         ImmutableSetMultimap.Builder<TopologyCluster, Link> linksBuilder =
                 ImmutableSetMultimap.builder();

         // Now scan through all the clusters
         for (TopologyCluster cluster : clusters.get().values()) {
             int i = cluster.id().index();

             // Scan through all the cluster vertexes.
             for (TopologyVertex vertex : clusterResults.get().clusterVertexes().get(i)) {
                 devicesBuilder.put(cluster, vertex.deviceId());
                 clusterBuilder.put(vertex.deviceId(), cluster);
             }

             // Scan through all the cluster edges.
             for (TopologyEdge edge : clusterResults.get().clusterEdges().get(i)) {
                 linksBuilder.put(cluster, edge.link());
             }
         }

         // Finalize all indexes.
         return new ClusterIndexes(clusterBuilder.build(),
                 devicesBuilder.build(), linksBuilder.build());
     }

     // Link weight for measuring link cost as hop count with indirect links
     // being as expensive as traversing the entire graph to assume the worst.
     private static class HopCountLinkWeight implements LinkWeight {
         private final int indirectLinkCost;

         HopCountLinkWeight(int indirectLinkCost) {
             this.indirectLinkCost = indirectLinkCost;
         }

         @Override
         public double weight(TopologyEdge edge) {
             // To force preference to use direct paths first, make indirect
             // links as expensive as the linear vertex traversal.
             return edge.link().state() ==
                     ACTIVE ? (edge.link().type() ==
                     INDIRECT ? indirectLinkCost : 1) : -1;
         }
     }

     // Link weight for preventing traversal over indirect links.
     private static class NoIndirectLinksWeight implements LinkWeight {
         @Override
         public double weight(TopologyEdge edge) {
             return (edge.link().state() == INACTIVE)
                     || (edge.link().type() == INDIRECT) ? -1 : 1;
         }
     }

     static final class ClusterIndexes {
         final ImmutableMap<DeviceId, TopologyCluster> clustersByDevice;
         final ImmutableSetMultimap<TopologyCluster, DeviceId> devicesByCluster;
         final ImmutableSetMultimap<TopologyCluster, Link> linksByCluster;

         public ClusterIndexes(
                 ImmutableMap<DeviceId, TopologyCluster> clustersByDevice,
                 ImmutableSetMultimap<TopologyCluster, DeviceId> devicesByCluster,
                 ImmutableSetMultimap<TopologyCluster, Link> linksByCluster) {
             this.clustersByDevice = clustersByDevice;
             this.devicesByCluster = devicesByCluster;
             this.linksByCluster = linksByCluster;
         }
     }

     @Override
     public String toString() {
         return toStringHelper(this)
                 .add("time", time)
                 .add("created", creationTime)
                 .add("computeCost", computeCost)
                 .add("clusters", clusterCount())
                 .add("devices", deviceCount())
                 .add("links", linkCount()).toString();
     }
 }
	/*
	* Copyright 2014-2015 Open Networking Laboratory
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	package org.onosproject.store.trivial;

	import static com.google.common.base.MoreObjects.toStringHelper;
	import static org.onlab.graph.GraphPathSearch.ALL_PATHS;
	import static org.onosproject.core.CoreService.CORE_PROVIDER_ID;
	import static org.onosproject.net.Link.State.ACTIVE;
	import static org.onosproject.net.Link.State.INACTIVE;
	import static org.onosproject.net.Link.Type.INDIRECT;

	import java.util.ArrayList;
	import java.util.List;
	import java.util.Map;
	import java.util.Set;

	import org.onlab.graph.DijkstraGraphSearch;
	import org.onlab.graph.GraphPathSearch;
	import org.onlab.graph.GraphPathSearch.Result;
	import org.onlab.graph.TarjanGraphSearch;
	import org.onlab.graph.TarjanGraphSearch.SCCResult;
	import org.onosproject.net.AbstractModel;
	import org.onosproject.net.ConnectPoint;
	import org.onosproject.net.DefaultPath;
	import org.onosproject.net.DeviceId;
	import org.onosproject.net.Link;
	import org.onosproject.net.Path;
	import org.onosproject.net.provider.ProviderId;
	import org.onosproject.net.topology.ClusterId;
	import org.onosproject.net.topology.DefaultTopologyCluster;
	import org.onosproject.net.topology.DefaultTopologyVertex;
	import org.onosproject.net.topology.GraphDescription;
	import org.onosproject.net.topology.LinkWeight;
	import org.onosproject.net.topology.Topology;
	import org.onosproject.net.topology.TopologyCluster;
	import org.onosproject.net.topology.TopologyEdge;
	import org.onosproject.net.topology.TopologyGraph;
	import org.onosproject.net.topology.TopologyVertex;

	import com.google.common.base.Supplier;
	import com.google.common.base.Suppliers;
	import com.google.common.collect.ImmutableMap;
	import com.google.common.collect.ImmutableSet;
	import com.google.common.collect.ImmutableSetMultimap;
	import com.google.common.collect.ImmutableSetMultimap.Builder;

	// FIXME: Move to onos-core-common when ready
	/**
	* Default implementation of the topology descriptor. This carries the backing
	* topology data.
	*/
	public class DefaultTopology extends AbstractModel implements Topology {

	private static final DijkstraGraphSearch<TopologyVertex, TopologyEdge> DIJKSTRA = new DijkstraGraphSearch<>();
	private static final TarjanGraphSearch<TopologyVertex, TopologyEdge> TARJAN = new TarjanGraphSearch<>();

	private final long time;
	private final long creationTime;
	private final long computeCost;
	private final TopologyGraph graph;

	private final LinkWeight weight;
	private final Supplier<SCCResult<TopologyVertex, TopologyEdge>> clusterResults;
	private final Supplier<ImmutableMap<ClusterId, TopologyCluster>> clusters;
	private final Supplier<ImmutableSet<ConnectPoint>> infrastructurePoints;
	private final Supplier<ImmutableSetMultimap<ClusterId, ConnectPoint>> broadcastSets;

	private final Supplier<ClusterIndexes> clusterIndexes;

	/**
	* Creates a topology descriptor attributed to the specified provider.
	*
	* @param providerId
	* identity of the provider
	* @param description
	* data describing the new topology
	*/
	DefaultTopology(ProviderId providerId, GraphDescription description) {
	super(providerId);
	this.time = description.timestamp();
	this.creationTime = description.creationTime();

	// Build the graph
	this.graph = new DefaultTopologyGraph(description.vertexes(),
	description.edges());

	this.clusterResults = Suppliers.memoize(() -> searchForClusters());
	this.clusters = Suppliers.memoize(() -> buildTopologyClusters());

	this.clusterIndexes = Suppliers.memoize(() -> buildIndexes());

	this.weight = new HopCountLinkWeight(graph.getVertexes().size());
	this.broadcastSets = Suppliers.memoize(() -> buildBroadcastSets());
	this.infrastructurePoints = Suppliers
	.memoize(() -> findInfrastructurePoints());
	this.computeCost = Math.max(0, System.nanoTime() - time);
	}

	@Override
	public long time() {
	return time;
	}

	@Override
	public long creationTime() {
	return creationTime;
	}

	@Override
	public long computeCost() {
	return computeCost;
	}

	@Override
	public int clusterCount() {
	return clusters.get().size();
	}

	@Override
	public int deviceCount() {
	return graph.getVertexes().size();
	}

	@Override
	public int linkCount() {
	return graph.getEdges().size();
	}

	private ImmutableMap<DeviceId, TopologyCluster> clustersByDevice() {
	return clusterIndexes.get().clustersByDevice;
	}

	private ImmutableSetMultimap<TopologyCluster, DeviceId> devicesByCluster() {
	return clusterIndexes.get().devicesByCluster;
	}

	private ImmutableSetMultimap<TopologyCluster, Link> linksByCluster() {
	return clusterIndexes.get().linksByCluster;
	}

	/**
	* Returns the backing topology graph.
	*
	* @return topology graph
	*/
	TopologyGraph getGraph() {
	return graph;
	}

	/**
	* Returns the set of topology clusters.
	*
	* @return set of clusters
	*/
	Set<TopologyCluster> getClusters() {
	return ImmutableSet.copyOf(clusters.get().values());
	}

	/**
	* Returns the specified topology cluster.
	*
	* @param clusterId cluster identifier
	*
	* @return topology cluster
	*/
	TopologyCluster getCluster(ClusterId clusterId) {
	return clusters.get().get(clusterId);
	}

	/**
	* Returns the topology cluster that contains the given device.
	*
	* @param deviceId device identifier
	*
	* @return topology cluster
	*/
	TopologyCluster getCluster(DeviceId deviceId) {
	return clustersByDevice().get(deviceId);
	}

	/**
	* Returns the set of cluster devices.
	*
	* @param cluster topology cluster
	*
	* @return cluster devices
	*/
	Set<DeviceId> getClusterDevices(TopologyCluster cluster) {
	return devicesByCluster().get(cluster);
	}

	/**
	* Returns the set of cluster links.
	*
	* @param cluster topology cluster
	*
	* @return cluster links
	*/
	Set<Link> getClusterLinks(TopologyCluster cluster) {
	return linksByCluster().get(cluster);
	}

	/**
	* Indicates whether the given point is an infrastructure link end-point.
	*
	* @param connectPoint connection point
	*
	* @return true if infrastructure
	*/
	boolean isInfrastructure(ConnectPoint connectPoint) {
	return infrastructurePoints.get().contains(connectPoint);
	}

	/**
	* Indicates whether the given point is part of a broadcast set.
	*
	* @param connectPoint connection point
	*
	* @return true if in broadcast set
	*/
	boolean isBroadcastPoint(ConnectPoint connectPoint) {
	// Any non-infrastructure, i.e. edge points are assumed to be OK.
	if (!isInfrastructure(connectPoint)) {
	return true;
	}

	// Find the cluster to which the device belongs.
	TopologyCluster cluster = clustersByDevice().get(connectPoint.deviceId());
	if (cluster == null) {
	throw new IllegalArgumentException("No cluster found for device "
	+ connectPoint.deviceId());
	}

	// If the broadcast set is null or empty, or if the point explicitly
	// belongs to it, return true;
	Set<ConnectPoint> points = broadcastSets.get().get(cluster.id());
	return (points == null) \|\| points.isEmpty() \|\| points.contains(connectPoint);
	}

	/**
	* Returns the size of the cluster broadcast set.
	*
	* @param clusterId cluster identifier
	*
	* @return size of the cluster broadcast set
	*/
	int broadcastSetSize(ClusterId clusterId) {
	return broadcastSets.get().get(clusterId).size();
	}

	/**
	* Returns the set of pre-computed shortest paths between source and
	* destination devices.
	*
	* @param src source device
	*
	* @param dst destination device
	*
	* @return set of shortest paths
	*/
	Set<Path> getPaths(DeviceId src, DeviceId dst) {
	return getPaths(src, dst, null);
	}

	/**
	* Computes on-demand the set of shortest paths between source and
	* destination devices.
	*
	* @param src source device
	*
	* @param dst destination device
	*
	* @param weight link weight function
	*
	* @return set of shortest paths
	*/
	Set<Path> getPaths(DeviceId src, DeviceId dst, LinkWeight weight) {
	final DefaultTopologyVertex srcV = new DefaultTopologyVertex(src);
	final DefaultTopologyVertex dstV = new DefaultTopologyVertex(dst);
	Set<TopologyVertex> vertices = graph.getVertexes();
	if (!vertices.contains(srcV) \|\| !vertices.contains(dstV)) {
	// src or dst not part of the current graph
	return ImmutableSet.of();
	}

	GraphPathSearch.Result<TopologyVertex, TopologyEdge> result =
	DIJKSTRA.search(graph, srcV, dstV, weight, ALL_PATHS);
	ImmutableSet.Builder<Path> builder = ImmutableSet.builder();
	for (org.onlab.graph.Path<TopologyVertex, TopologyEdge> path : result.paths()) {
	builder.add(networkPath(path));
	}
	return builder.build();
	}

	// Converts graph path to a network path with the same cost.
	private Path networkPath(org.onlab.graph.Path<TopologyVertex, TopologyEdge> path) {
	List<Link> links = new ArrayList<>();
	for (TopologyEdge edge : path.edges()) {
	links.add(edge.link());
	}
	return new DefaultPath(CORE_PROVIDER_ID, links, path.cost());
	}

	// Searches for SCC clusters in the network topology graph using Tarjan
	// algorithm.
	private SCCResult<TopologyVertex, TopologyEdge> searchForClusters() {
	return TARJAN.search(graph, new NoIndirectLinksWeight());
	}

	// Builds the topology clusters and returns the id-cluster bindings.
	private ImmutableMap<ClusterId, TopologyCluster> buildTopologyClusters() {
	ImmutableMap.Builder<ClusterId, TopologyCluster> clusterBuilder = ImmutableMap.builder();
	SCCResult<TopologyVertex, TopologyEdge> results = clusterResults.get();
	// Extract both vertexes and edges from the results; the lists form
	// pairs along the same index.
	List<Set<TopologyVertex>> clusterVertexes = results.clusterVertexes();
	List<Set<TopologyEdge>> clusterEdges = results.clusterEdges();

	// Scan over the lists and create a cluster from the results.
	for (int i = 0, n = results.clusterCount(); i < n; i++) {
	Set<TopologyVertex> vertexSet = clusterVertexes.get(i);
	Set<TopologyEdge> edgeSet = clusterEdges.get(i);

	ClusterId cid = ClusterId.clusterId(i);
	DefaultTopologyCluster cluster = new DefaultTopologyCluster(cid,
	vertexSet.size(),
	edgeSet.size(),
	findRoot(vertexSet));
	clusterBuilder.put(cid, cluster);
	}
	return clusterBuilder.build();
	}

	// Finds the vertex whose device id is the lexicographical minimum in the
	// specified set.
	private TopologyVertex findRoot(Set<TopologyVertex> vertexSet) {
	TopologyVertex minVertex = null;
	for (TopologyVertex vertex : vertexSet) {
	if ((minVertex == null) \|\| (minVertex.deviceId().toString()
	.compareTo(minVertex.deviceId().toString()) < 0)) {
	minVertex = vertex;
	}
	}
	return minVertex;
	}

	// Processes a map of broadcast sets for each cluster.
	private ImmutableSetMultimap<ClusterId, ConnectPoint> buildBroadcastSets() {
	Builder<ClusterId, ConnectPoint> builder = ImmutableSetMultimap.builder();
	for (TopologyCluster cluster : clusters.get().values()) {
	addClusterBroadcastSet(cluster, builder);
	}
	return builder.build();
	}

	// Finds all broadcast points for the cluster. These are those connection
	// points which lie along the shortest paths between the cluster root and
	// all other devices within the cluster.
	private void addClusterBroadcastSet(TopologyCluster cluster, Builder<ClusterId, ConnectPoint> builder) {
	// Use the graph root search results to build the broadcast set.
	Result<TopologyVertex, TopologyEdge> result =
	DIJKSTRA.search(graph, cluster.root(), null, weight, 1);
	for (Map.Entry<TopologyVertex, Set<TopologyEdge>> entry : result.parents().entrySet()) {
	TopologyVertex vertex = entry.getKey();

	// Ignore any parents that lead outside the cluster.
	if (clustersByDevice().get(vertex.deviceId()) != cluster) {
	continue;
	}

	// Ignore any back-link sets that are empty.
	Set<TopologyEdge> parents = entry.getValue();
	if (parents.isEmpty()) {
	continue;
	}

	// Use the first back-link source and destinations to add to the
	// broadcast set.
	Link link = parents.iterator().next().link();
	builder.put(cluster.id(), link.src());
	builder.put(cluster.id(), link.dst());
	}
	}

	// Collects and returns an set of all infrastructure link end-points.
	private ImmutableSet<ConnectPoint> findInfrastructurePoints() {
	ImmutableSet.Builder<ConnectPoint> builder = ImmutableSet.builder();
	for (TopologyEdge edge : graph.getEdges()) {
	builder.add(edge.link().src());
	builder.add(edge.link().dst());
	}
	return builder.build();
	}

	// Builds cluster-devices, cluster-links and device-cluster indexes.
	private ClusterIndexes buildIndexes() {
	// Prepare the index builders
	ImmutableMap.Builder<DeviceId, TopologyCluster> clusterBuilder =
	ImmutableMap.builder();
	ImmutableSetMultimap.Builder<TopologyCluster, DeviceId> devicesBuilder =
	ImmutableSetMultimap.builder();
	ImmutableSetMultimap.Builder<TopologyCluster, Link> linksBuilder =
	ImmutableSetMultimap.builder();

	// Now scan through all the clusters
	for (TopologyCluster cluster : clusters.get().values()) {
	int i = cluster.id().index();

	// Scan through all the cluster vertexes.
	for (TopologyVertex vertex : clusterResults.get().clusterVertexes().get(i)) {
	devicesBuilder.put(cluster, vertex.deviceId());
	clusterBuilder.put(vertex.deviceId(), cluster);
	}

	// Scan through all the cluster edges.
	for (TopologyEdge edge : clusterResults.get().clusterEdges().get(i)) {
	linksBuilder.put(cluster, edge.link());
	}
	}

	// Finalize all indexes.
	return new ClusterIndexes(clusterBuilder.build(),
	devicesBuilder.build(), linksBuilder.build());
	}

	// Link weight for measuring link cost as hop count with indirect links
	// being as expensive as traversing the entire graph to assume the worst.
	private static class HopCountLinkWeight implements LinkWeight {
	private final int indirectLinkCost;

	HopCountLinkWeight(int indirectLinkCost) {
	this.indirectLinkCost = indirectLinkCost;
	}

	@Override
	public double weight(TopologyEdge edge) {
	// To force preference to use direct paths first, make indirect
	// links as expensive as the linear vertex traversal.
	return edge.link().state() ==
	ACTIVE ? (edge.link().type() ==
	INDIRECT ? indirectLinkCost : 1) : -1;
	}
	}

	// Link weight for preventing traversal over indirect links.
	private static class NoIndirectLinksWeight implements LinkWeight {
	@Override
	public double weight(TopologyEdge edge) {
	return (edge.link().state() == INACTIVE)
	\|\| (edge.link().type() == INDIRECT) ? -1 : 1;
	}
	}

	static final class ClusterIndexes {
	final ImmutableMap<DeviceId, TopologyCluster> clustersByDevice;
	final ImmutableSetMultimap<TopologyCluster, DeviceId> devicesByCluster;
	final ImmutableSetMultimap<TopologyCluster, Link> linksByCluster;

	public ClusterIndexes(
	ImmutableMap<DeviceId, TopologyCluster> clustersByDevice,
	ImmutableSetMultimap<TopologyCluster, DeviceId> devicesByCluster,
	ImmutableSetMultimap<TopologyCluster, Link> linksByCluster) {
	this.clustersByDevice = clustersByDevice;
	this.devicesByCluster = devicesByCluster;
	this.linksByCluster = linksByCluster;
	}
	}

	@Override
	public String toString() {
	return toStringHelper(this)
	.add("time", time)
	.add("created", creationTime)
	.add("computeCost", computeCost)
	.add("clusters", clusterCount())
	.add("devices", deviceCount())
	.add("links", linkCount()).toString();
	}
	}