Working on simple topology manager and provider

+package org.onlab.onos.event;
+
+import com.google.common.collect.Lists;
+
+import java.util.List;
+import java.util.Timer;
+import java.util.TimerTask;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * Base implementation of an event accumulator. It allows triggering based on
+ * event inter-arrival time threshold, maximum batch life threshold and maximum
+ * batch size.
+ */
+public abstract class AbstractEventAccumulator implements EventAccumulator {
+
+    private final Timer timer;
+    private final int maxEvents;
+    private final int maxBatchMillis;
+    private final int maxIdleMillis;
+
+    private TimerTask idleTask = new ProcessorTask();
+    private TimerTask maxTask = new ProcessorTask();
+
+    private List<Event> events = Lists.newArrayList();
+
+    /**
+     * Creates an event accumulator capable of triggering on the specified
+     * thresholds.
+     *
+     * @param timer          timer to use for scheduling check-points
+     * @param maxEvents      maximum number of events to accumulate before
+     *                       processing is triggered
+     * @param maxBatchMillis maximum number of millis allowed since the first
+     *                       event before processing is triggered
+     * @param maxIdleMillis  maximum number millis between events before
+     *                       processing is triggered
+     */
+    protected AbstractEventAccumulator(Timer timer, int maxEvents,
+                                       int maxBatchMillis, int maxIdleMillis) {
+        this.timer = checkNotNull(timer, "Timer cannot be null");
+
+        checkArgument(maxEvents > 1, "Maximum number of events must be > 1");
+        checkArgument(maxBatchMillis > 0, "Maximum millis must be positive");
+        checkArgument(maxIdleMillis > 0, "Maximum idle millis must be positive");
+
+        this.maxEvents = maxEvents;
+        this.maxBatchMillis = maxBatchMillis;
+        this.maxIdleMillis = maxIdleMillis;
+    }
+
+    @Override
+    public void add(Event event) {
+        idleTask = cancelIfActive(idleTask);
+        events.add(event);
+
+        // Did we hit the max event threshold?
+        if (events.size() == maxEvents) {
+            maxTask = cancelIfActive(maxTask);
+            schedule(1);
+        } else {
+            // Otherwise, schedule idle task and if this is a first event
+            // also schedule the max batch age task.
+            idleTask = schedule(maxIdleMillis);
+            if (events.size() == 1) {
+                maxTask = schedule(maxBatchMillis);
+            }
+        }
+    }
+
+    // Schedules a new processor task given number of millis in the future.
+    private TimerTask schedule(int millis) {
+        TimerTask task = new ProcessorTask();
+        timer.schedule(task, millis);
+        return task;
+    }
+
+    // Cancels the specified task if it is active.
+    private TimerTask cancelIfActive(TimerTask task) {
+        if (task != null) {
+            task.cancel();
+        }
+        return task;
+    }
+
+    // Task for triggering processing of accumulated events
+    private class ProcessorTask extends TimerTask {
+        @Override
+        public void run() {
+            idleTask = cancelIfActive(idleTask);
+            maxTask = cancelIfActive(maxTask);
+            processEvents(finalizeCurrentBatch());
+        }
+    }
+
+    // Demotes and returns the current batch of events and promotes a new one.
+    private synchronized List<Event> finalizeCurrentBatch() {
+        List<Event> toBeProcessed = events;
+        events = Lists.newArrayList();
+        return toBeProcessed;
+    }
+
+    /**
+     * Returns the backing timer.
+     *
+     * @return backing timer
+     */
+    public Timer timer() {
+        return timer;
+    }
+
+    /**
+     * Returns the maximum number of events allowed to accumulate before
+     * processing is triggered.
+     *
+     * @return max number of events
+     */
+    public int maxEvents() {
+        return maxEvents;
+    }
+
+    /**
+     * Returns the maximum number of millis allowed to expire since the first
+     * event before processing is triggered.
+     *
+     * @return max number of millis a batch is allowed to last
+     */
+    public int maxBatchMillis() {
+        return maxBatchMillis;
+    }
+
+    /**
+     * Returns the maximum number of millis allowed to expire since the last
+     * event arrival before processing is triggered.
+     *
+     * @return max number of millis since the last event
+     */
+    public int maxIdleMillis() {
+        return maxIdleMillis;
+    }
+}

+package org.onlab.onos.event;
+
+import java.util.List;
+
+/**
+ * Abstraction of an accumulator capable of collecting events and at some
+ * point in time triggers processing of all previously accumulated events.
+ */
+public interface EventAccumulator {
+
+    /**
+     * Adds an event to the current batch. This operation may, or may not
+     * trigger processing of the current batch of events.
+     *
+     * @param event event to be added to the current batch
+     */
+    void add(Event event);
+
+    /**
+     * Processes the specified list of accumulated events.
+     *
+     * @param events list of accumulated events
+     */
+    void processEvents(List<Event> events);
+
+}

 package org.onlab.onos.net.trivial.impl;
 package org.onlab.onos.net.trivial.impl;
 
 
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.ImmutableSet;
-import com.google.common.collect.Multimap;
+import com.google.common.collect.Maps;
+import com.google.common.collect.Sets;
+import org.onlab.graph.AdjacencyListsGraph;
+import org.onlab.graph.DijkstraGraphSearch;
 import org.onlab.graph.Graph;
 import org.onlab.graph.Graph;
 import org.onlab.graph.GraphPathSearch;
 import org.onlab.graph.GraphPathSearch;
+import org.onlab.onos.net.ConnectPoint;
+import org.onlab.onos.net.Device;
 import org.onlab.onos.net.DeviceId;
 import org.onlab.onos.net.DeviceId;
 import org.onlab.onos.net.Link;
 import org.onlab.onos.net.Link;
 import org.onlab.onos.net.topology.ClusterId;
 import org.onlab.onos.net.topology.ClusterId;
+import org.onlab.onos.net.topology.LinkWeight;
 import org.onlab.onos.net.topology.TopoEdge;
 import org.onlab.onos.net.topology.TopoEdge;
 import org.onlab.onos.net.topology.TopoVertex;
 import org.onlab.onos.net.topology.TopoVertex;
 import org.onlab.onos.net.topology.TopologyCluster;
 import org.onlab.onos.net.topology.TopologyCluster;
 import org.onlab.onos.net.topology.TopologyDescription;
 import org.onlab.onos.net.topology.TopologyDescription;
 
 
 import java.util.Map;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 import java.util.Set;
 
 
+import static com.google.common.base.MoreObjects.toStringHelper;
+import static org.onlab.graph.GraphPathSearch.Result;
+import static org.onlab.onos.net.Link.Type.INDIRECT;
+
 /**
 /**
  * Default implementation of an immutable topology data carrier.
  * Default implementation of an immutable topology data carrier.
  */
  */
-public class DefaultTopologyDescription implements TopologyDescription {
+class DefaultTopologyDescription implements TopologyDescription {
+
+    private static final GraphPathSearch<TopoVertex, TopoEdge> DIJKSTRA =
+            new DijkstraGraphSearch<>();
 
 
     private final long nanos;
     private final long nanos;
+    private final Map<DeviceId, TopoVertex> vertexesById = Maps.newHashMap();
     private final Graph<TopoVertex, TopoEdge> graph;
     private final Graph<TopoVertex, TopoEdge> graph;
-    private final Map<DeviceId, GraphPathSearch.Result<TopoVertex, TopoEdge>> results;
+    private final Map<DeviceId, Result<TopoVertex, TopoEdge>> results;
     private final Map<ClusterId, TopologyCluster> clusters;
     private final Map<ClusterId, TopologyCluster> clusters;
-    private final Multimap<ClusterId, DeviceId> clusterDevices;
-    private final Multimap<ClusterId, Link> clusterLinks;
-    private final Map<DeviceId, TopologyCluster> deviceClusters;
-
-    public DefaultTopologyDescription(long nanos, Graph<TopoVertex, TopoEdge> graph,
-                                      Map<DeviceId, GraphPathSearch.Result<TopoVertex, TopoEdge>> results,
-                                      Map<ClusterId, TopologyCluster> clusters,
-                                      Multimap<ClusterId, DeviceId> clusterDevices,
-                                      Multimap<ClusterId, Link> clusterLinks,
-                                      Map<DeviceId, TopologyCluster> deviceClusters) {
+//    private final Multimap<ClusterId, DeviceId> clusterDevices;
+//    private final Multimap<ClusterId, Link> clusterLinks;
+//    private final Map<DeviceId, TopologyCluster> deviceClusters;
+
+
+    DefaultTopologyDescription(long nanos, Iterable<Device> devices, Iterable<Link> links) {
         this.nanos = nanos;
         this.nanos = nanos;
-        this.graph = graph;
-        this.results = results;
-        this.clusters = clusters;
-        this.clusterDevices = clusterDevices;
-        this.clusterLinks = clusterLinks;
-        this.deviceClusters = deviceClusters;
+        this.graph = buildGraph(devices, links);
+        this.results = computeDefaultPaths();
+        this.clusters = computeClusters();
+//        this.clusterDevices = clusterDevices;
+//        this.clusterLinks = clusterLinks;
+//        this.deviceClusters = deviceClusters;
+    }
+
+    // Constructs the topology graph using the supplied devices and links.
+    private Graph<TopoVertex, TopoEdge> buildGraph(Iterable<Device> devices,
+                                                   Iterable<Link> links) {
+        Graph<TopoVertex, TopoEdge> graph =
+                new AdjacencyListsGraph<>(buildVertexes(devices),
+                                          buildEdges(links));
+        return graph;
+    }
+
+    // Builds a set of topology vertexes from the specified list of devices
+    private Set<TopoVertex> buildVertexes(Iterable<Device> devices) {
+        Set<TopoVertex> vertexes = Sets.newHashSet();
+        for (Device device : devices) {
+            TopoVertex vertex = new TVertex(device.id());
+            vertexesById.put(vertex.deviceId(), vertex);
+            vertexes.add(vertex);
+        }
+        return vertexes;
+    }
+
+    // Builds a set of topology vertexes from the specified list of links
+    private Set<TopoEdge> buildEdges(Iterable<Link> links) {
+        Set<TopoEdge> edges = Sets.newHashSet();
+        for (Link link : links) {
+            edges.add(new TEdge(vertexOf(link.src()), vertexOf(link.dst()), link));
+        }
+        return edges;
+    }
+
+    // Computes the default shortest paths for all source/dest pairs using
+    // the multi-path Dijkstra and hop-count as path cost.
+    private Map<DeviceId, Result<TopoVertex, TopoEdge>> computeDefaultPaths() {
+        LinkWeight weight = new HopCountLinkWeight(graph.getVertexes().size());
+        Map<DeviceId, Result<TopoVertex, TopoEdge>> results = Maps.newHashMap();
+
+        // Search graph paths for each source to all destinations.
+        for (TopoVertex src : vertexesById.values()) {
+            results.put(src.deviceId(), DIJKSTRA.search(graph, src, null, weight));
+        }
+        return results;
+    }
+
+    // Computes topology SCC clusters using Tarjan algorithm.
+    private Map<ClusterId, TopologyCluster> computeClusters() {
+        Map<ClusterId, TopologyCluster> clusters = Maps.newHashMap();
+        return clusters;
+    }
+
+    // Fetches a vertex corresponding to the given connection point device.
+    private TopoVertex vertexOf(ConnectPoint connectPoint) {
+        DeviceId id = connectPoint.deviceId();
+        TopoVertex vertex = vertexesById.get(id);
+        if (vertex == null) {
+            // If vertex does not exist, create one and register it.
+            vertex = new TVertex(id);
+            vertexesById.put(id, vertex);
+        }
+        return vertex;
     }
     }
 
 
     @Override
     @Override
@@ -54,7 +125,7 @@ public class DefaultTopologyDescription implements TopologyDescription {
     }
     }
 
 
     @Override
     @Override
-    public GraphPathSearch.Result<TopoVertex, TopoEdge> pathResults(DeviceId srcDeviceId) {
+    public Result<TopoVertex, TopoEdge> pathResults(DeviceId srcDeviceId) {
         return results.get(srcDeviceId);
         return results.get(srcDeviceId);
     }
     }
 
 
@@ -75,6 +146,105 @@ public class DefaultTopologyDescription implements TopologyDescription {
 
 
     @Override
     @Override
     public TopologyCluster clusterFor(DeviceId deviceId) {
     public TopologyCluster clusterFor(DeviceId deviceId) {
-        return deviceClusters.get(deviceId);
+        return null; // deviceClusters.get(deviceId);
+    }
+
+    // Implementation of the topology vertex backed by a device id
+    private static class TVertex implements TopoVertex {
+
+        private final DeviceId deviceId;
+
+        public TVertex(DeviceId deviceId) {
+            this.deviceId = deviceId;
+        }
+
+        @Override
+        public DeviceId deviceId() {
+            return deviceId;
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(deviceId);
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            if (obj instanceof TVertex) {
+                final TVertex other = (TVertex) obj;
+                return Objects.equals(this.deviceId, other.deviceId);
+            }
+            return false;
+        }
+
+        @Override
+        public String toString() {
+            return deviceId.toString();
+        }
+    }
+
+    // Implementation of the topology edge backed by a link
+    private class TEdge implements TopoEdge {
+        private final Link link;
+        private final TopoVertex src;
+        private final TopoVertex dst;
+
+        public TEdge(TopoVertex src, TopoVertex dst, Link link) {
+            this.src = src;
+            this.dst = dst;
+            this.link = link;
+        }
+
+        @Override
+        public Link link() {
+            return link;
+        }
+
+        @Override
+        public TopoVertex src() {
+            return src;
+        }
+
+        @Override
+        public TopoVertex dst() {
+            return dst;
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(link);
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            if (obj instanceof TEdge) {
+                final TEdge other = (TEdge) obj;
+                return Objects.equals(this.link, other.link);
+            }
+            return false;
+        }
+
+        @Override
+        public String toString() {
+            return toStringHelper(this).add("src", src).add("dst", dst).toString();
+        }
     }
     }
+
+    // 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 class HopCountLinkWeight implements LinkWeight {
+        private final int indirectLinkCost;
+
+        public HopCountLinkWeight(int indirectLinkCost) {
+            this.indirectLinkCost = indirectLinkCost;
+        }
+
+        @Override
+        public double weight(TopoEdge edge) {
+            // To force preference to use direct paths first, make indirect
+            // links as expensive as the linear vertex traversal.
+            return edge.link().type() == INDIRECT ? indirectLinkCost : 1;
+        }
+    }
+
 }
 }

@@ -28,7 +28,8 @@ import static com.google.common.base.Preconditions.checkArgument;
 import static org.onlab.onos.net.device.DeviceEvent.Type.*;
 import static org.onlab.onos.net.device.DeviceEvent.Type.*;
 
 
 /**
 /**
-
+ * Manages inventory of infrastructure DEVICES using trivial in-memory
+ * structures implementation.
  */
  */
 class SimpleDeviceStore {
 class SimpleDeviceStore {
 
 

@@ -25,7 +25,7 @@ import static org.onlab.onos.net.link.LinkEvent.Type.LINK_REMOVED;
 import static org.onlab.onos.net.link.LinkEvent.Type.LINK_UPDATED;
 import static org.onlab.onos.net.link.LinkEvent.Type.LINK_UPDATED;
 
 
 /**
 /**
- * Manages inventory of infrastructure links using trivial in-memory link
+ * Manages inventory of infrastructure links using trivial in-memory structures
  * implementation.
  * implementation.
  */
  */
 class SimpleLinkStore {
 class SimpleLinkStore {

@@ -153,6 +153,9 @@ public class SimpleTopologyManager
         public void topologyChanged(TopologyDescription topoDescription,
         public void topologyChanged(TopologyDescription topoDescription,
                                     List<Event> reasons) {
                                     List<Event> reasons) {
             checkNotNull(topoDescription, "Topology description cannot be null");
             checkNotNull(topoDescription, "Topology description cannot be null");
+
+            log.info("Topology changed due to: {}", // to be removed soon
+                     reasons == null ? "initial compute" : reasons);
             TopologyEvent event = store.updateTopology(topoDescription, reasons);
             TopologyEvent event = store.updateTopology(topoDescription, reasons);
             if (event != null) {
             if (event != null) {
                 log.info("Topology changed due to: {}",
                 log.info("Topology changed due to: {}",

+package org.onlab.onos.net.trivial.impl;
+
+import org.apache.felix.scr.annotations.Activate;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Deactivate;
+import org.apache.felix.scr.annotations.Reference;
+import org.apache.felix.scr.annotations.ReferenceCardinality;
+import org.onlab.onos.event.AbstractEventAccumulator;
+import org.onlab.onos.event.Event;
+import org.onlab.onos.event.EventAccumulator;
+import org.onlab.onos.net.device.DeviceEvent;
+import org.onlab.onos.net.device.DeviceListener;
+import org.onlab.onos.net.device.DeviceService;
+import org.onlab.onos.net.link.LinkEvent;
+import org.onlab.onos.net.link.LinkListener;
+import org.onlab.onos.net.link.LinkService;
+import org.onlab.onos.net.provider.AbstractProvider;
+import org.onlab.onos.net.provider.ProviderId;
+import org.onlab.onos.net.topology.TopologyDescription;
+import org.onlab.onos.net.topology.TopologyProvider;
+import org.onlab.onos.net.topology.TopologyProviderRegistry;
+import org.onlab.onos.net.topology.TopologyProviderService;
+import org.slf4j.Logger;
+
+import java.util.List;
+import java.util.Timer;
+import java.util.concurrent.ExecutorService;
+
+import static java.util.concurrent.Executors.newFixedThreadPool;
+import static org.onlab.onos.net.device.DeviceEvent.Type.*;
+import static org.onlab.util.Tools.namedThreads;
+import static org.slf4j.LoggerFactory.getLogger;
+
+/**
+ * Simple implementation of a network topology provider/computor.
+ */
+@Component(immediate = true)
+public class SimpleTopologyProvider extends AbstractProvider
+        implements TopologyProvider {
+
+    // TODO: make these configurable
+    private static final int MAX_EVENTS = 100;
+    private static final int MAX_IDLE_MS = 50;
+    private static final int MAX_BATCH_MS = 200;
+    private static final int MAX_THREADS = 8;
+
+    // FIXME: Replace with a system-wide timer instance
+    private static final Timer TIMER = new Timer();
+
+    private final Logger log = getLogger(getClass());
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected TopologyProviderRegistry providerRegistry;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected DeviceService deviceService;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected LinkService linkService;
+
+    private volatile boolean isStarted = false;
+
+    private TopologyProviderService providerService;
+    private DeviceListener deviceListener = new InnerDeviceListener();
+    private LinkListener linkListener = new InnerLinkListener();
+
+    private EventAccumulator accumulator;
+    private ExecutorService executor;
+
+    /**
+     * Creates a provider with the supplier identifier.
+     */
+    public SimpleTopologyProvider() {
+        super(new ProviderId("org.onlab.onos.provider.topology"));
+    }
+
+    @Activate
+    public synchronized void activate() {
+        executor = newFixedThreadPool(MAX_THREADS, namedThreads("topo-compute-%d"));
+        accumulator = new TopologyChangeAccumulator();
+
+        providerService = providerRegistry.register(this);
+        deviceService.addListener(deviceListener);
+        linkService.addListener(linkListener);
+
+        isStarted = true;
+        triggerTopologyBuild(null);
+        log.info("Started");
+    }
+
+    @Deactivate
+    public synchronized void deactivate() {
+        deviceService.removeListener(deviceListener);
+        linkService.removeListener(linkListener);
+        providerRegistry.unregister(this);
+        providerService = null;
+
+        executor.shutdownNow();
+        executor = null;
+
+        isStarted = false;
+        log.info("Stopped");
+    }
+
+    /**
+     * Triggers assembly of topology data citing the specified events as the
+     * reason.
+     *
+     * @param reasons events which triggered the topology change
+     */
+    private void triggerTopologyBuild(List<Event> reasons) {
+        executor.execute(new TopologyBuilderTask(reasons));
+    }
+
+    // Builds the topology using the latest device and link information
+    // and citing the specified events as reasons for the change.
+    private void buildTopology(List<Event> reasons) {
+        log.info("YO! Computing topology");
+        if (isStarted) {
+            TopologyDescription desc =
+                    new DefaultTopologyDescription(System.nanoTime(),
+                                                   deviceService.getDevices(),
+                                                   linkService.getLinks());
+            providerService.topologyChanged(desc, reasons);
+        }
+    }
+
+    // Callback for device events
+    private class InnerDeviceListener implements DeviceListener {
+        @Override
+        public void event(DeviceEvent event) {
+            DeviceEvent.Type type = event.type();
+            if (type == DEVICE_ADDED || type == DEVICE_REMOVED ||
+                    type == DEVICE_AVAILABILITY_CHANGED) {
+                accumulator.add(event);
+            }
+        }
+    }
+
+    // Callback for link events
+    private class InnerLinkListener implements LinkListener {
+        @Override
+        public void event(LinkEvent event) {
+            accumulator.add(event);
+        }
+    }
+
+    // Event accumulator for paced triggering of topology assembly.
+    private class TopologyChangeAccumulator
+            extends AbstractEventAccumulator implements EventAccumulator {
+
+        TopologyChangeAccumulator() {
+            super(TIMER, MAX_EVENTS, MAX_BATCH_MS, MAX_IDLE_MS);
+        }
+
+        @Override
+        public void processEvents(List<Event> events) {
+            triggerTopologyBuild(events);
+        }
+
+    }
+
+    // Task for building topology data in a separate thread.
+    private class TopologyBuilderTask implements Runnable {
+        private final List<Event> reasons;
+
+        public TopologyBuilderTask(List<Event> reasons) {
+            this.reasons = reasons;
+        }
+
+        @Override
+        public void run() {
+            buildTopology(reasons);
+        }
+    }
+
+}

@@ -18,9 +18,9 @@ import java.util.Set;
 
 
 /**
 /**
  * Manages inventory of topology snapshots using trivial in-memory
  * Manages inventory of topology snapshots using trivial in-memory
- * implementation.
+ * structures implementation.
  */
  */
-public class SimpleTopologyStore {
+class SimpleTopologyStore {
 
 
     private volatile DefaultTopology current;
     private volatile DefaultTopology current;
 
 
@@ -35,10 +35,12 @@ public class SimpleTopologyStore {
 
 
     /**
     /**
      * Indicates whether the topology is the latest.
      * Indicates whether the topology is the latest.
+     *
      * @param topology topology descriptor
      * @param topology topology descriptor
      * @return true if topology is the most recent one
      * @return true if topology is the most recent one
      */
      */
     boolean isLatest(Topology topology) {
     boolean isLatest(Topology topology) {
+        // Topology is current only if it is the same as our current topology
         return topology == current;
         return topology == current;
     }
     }
 
 
@@ -117,7 +119,8 @@ public class SimpleTopologyStore {
      * @param reasons         list of events that triggered the update
      * @param reasons         list of events that triggered the update
      * @return topology update event or null if the description is old
      * @return topology update event or null if the description is old
      */
      */
-    TopologyEvent updateTopology(TopologyDescription topoDescription, List<Event> reasons) {
+    TopologyEvent updateTopology(TopologyDescription topoDescription,
+                                 List<Event> reasons) {
         return null;
         return null;
     }
     }
 
 

@@ -15,7 +15,8 @@ import static com.google.common.base.Preconditions.checkNotNull;
  * @param <V> vertex type
  * @param <V> vertex type
  * @param <E> edge type
  * @param <E> edge type
  */
  */
-public class AdjacencyListsGraph<V extends Vertex, E extends Edge<V>> implements Graph<V, E> {
+public class AdjacencyListsGraph<V extends Vertex, E extends Edge<V>>
+        implements Graph<V, E> {
 
 
     private final Set<V> vertexes;
     private final Set<V> vertexes;
     private final Set<E> edges;
     private final Set<E> edges;