Checking in GossipHostStore. The implementation is only partly done and not fully distributed, yet.

+package org.onlab.onos.store.host.impl;
+
+import com.google.common.collect.HashMultimap;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Multimap;
+import com.google.common.collect.Sets;
+
+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.apache.felix.scr.annotations.Service;
+import org.onlab.onos.cluster.ClusterService;
+import org.onlab.onos.net.Annotations;
+import org.onlab.onos.net.ConnectPoint;
+import org.onlab.onos.net.DefaultHost;
+import org.onlab.onos.net.DeviceId;
+import org.onlab.onos.net.Host;
+import org.onlab.onos.net.HostId;
+import org.onlab.onos.net.HostLocation;
+import org.onlab.onos.net.host.HostClockService;
+import org.onlab.onos.net.host.HostDescription;
+import org.onlab.onos.net.host.HostEvent;
+import org.onlab.onos.net.host.HostStore;
+import org.onlab.onos.net.host.HostStoreDelegate;
+import org.onlab.onos.net.host.PortAddresses;
+import org.onlab.onos.net.provider.ProviderId;
+import org.onlab.onos.store.AbstractStore;
+import org.onlab.onos.store.Timestamp;
+import org.onlab.onos.store.cluster.messaging.ClusterCommunicationService;
+import org.onlab.onos.store.common.impl.Timestamped;
+import org.onlab.packet.IpPrefix;
+import org.onlab.packet.MacAddress;
+import org.onlab.packet.VlanId;
+import org.slf4j.Logger;
+
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+
+import static org.onlab.onos.net.host.HostEvent.Type.*;
+import static org.slf4j.LoggerFactory.getLogger;
+
+/**
+ * Manages inventory of end-station hosts in distributed data store
+ * that uses optimistic replication and gossip based techniques.
+ */
+@Component(immediate = true)
+@Service
+public class GossipHostStore
+        extends AbstractStore<HostEvent, HostStoreDelegate>
+        implements HostStore {
+
+    private final Logger log = getLogger(getClass());
+
+    // Host inventory
+    private final Map<HostId, StoredHost> hosts = new ConcurrentHashMap<>(2000000, 0.75f, 16);
+
+    private final Map<HostId, Timestamped<Host>> removedHosts = new ConcurrentHashMap<>(2000000, 0.75f, 16);
+
+    // Hosts tracked by their location
+    private final Multimap<ConnectPoint, Host> locations = HashMultimap.create();
+
+    private final Map<ConnectPoint, PortAddresses> portAddresses =
+            new ConcurrentHashMap<>();
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected HostClockService hostClockService;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected ClusterCommunicationService clusterCommunicator;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected ClusterService clusterService;
+
+    @Activate
+    public void activate() {
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        log.info("Stopped");
+    }
+
+    @Override
+    public HostEvent createOrUpdateHost(ProviderId providerId, HostId hostId,
+                                        HostDescription hostDescription) {
+        Timestamp timestamp = hostClockService.getTimestamp(hostId);
+        return createOrUpdateHostInternal(providerId, hostId, hostDescription, timestamp);
+        // TODO: tell peers.
+    }
+
+    private HostEvent createOrUpdateHostInternal(ProviderId providerId, HostId hostId,
+                                        HostDescription hostDescription, Timestamp timestamp) {
+        StoredHost host = hosts.get(hostId);
+        if (host == null) {
+            return createHost(providerId, hostId, hostDescription, timestamp);
+        }
+        return updateHost(providerId, host, hostDescription, timestamp);
+    }
+
+    // creates a new host and sends HOST_ADDED
+    private HostEvent createHost(ProviderId providerId, HostId hostId,
+                                 HostDescription descr, Timestamp timestamp) {
+        synchronized (this) {
+            // If this host was previously removed, first ensure
+            // this new request is "newer"
+            if (removedHosts.containsKey(hostId)) {
+                if (removedHosts.get(hostId).isNewer(timestamp)) {
+                    return null;
+                } else {
+                    removedHosts.remove(hostId);
+                }
+            }
+            StoredHost newhost = new StoredHost(providerId, hostId,
+                    descr.hwAddress(),
+                    descr.vlan(),
+                    new Timestamped<>(descr.location(), timestamp),
+                    ImmutableSet.of(descr.ipAddress()));
+            hosts.put(hostId, newhost);
+            locations.put(descr.location(), newhost);
+            return new HostEvent(HOST_ADDED, newhost);
+        }
+    }
+
+    // checks for type of update to host, sends appropriate event
+    private HostEvent updateHost(ProviderId providerId, StoredHost host,
+                                 HostDescription descr, Timestamp timestamp) {
+        HostEvent event;
+        if (!host.location.isNewer(timestamp) && !host.location().equals(descr.location())) {
+            host.setLocation(new Timestamped<>(descr.location(), timestamp));
+            return new HostEvent(HOST_MOVED, host);
+        }
+
+        if (host.ipAddresses().contains(descr.ipAddress())) {
+            return null;
+        }
+
+        Set<IpPrefix> addresses = new HashSet<>(host.ipAddresses());
+        addresses.add(descr.ipAddress());
+        StoredHost updated = new StoredHost(providerId, host.id(),
+                                            host.mac(), host.vlan(),
+                                            host.location, addresses);
+        event = new HostEvent(HOST_UPDATED, updated);
+        synchronized (this) {
+            hosts.put(host.id(), updated);
+            locations.remove(host.location(), host);
+            locations.put(updated.location(), updated);
+        }
+        return event;
+    }
+
+    @Override
+    public HostEvent removeHost(HostId hostId) {
+        Timestamp timestamp = hostClockService.getTimestamp(hostId);
+        return removeHostInternal(hostId, timestamp);
+        // TODO: tell peers
+    }
+
+    private HostEvent removeHostInternal(HostId hostId, Timestamp timestamp) {
+        synchronized (this) {
+            Host host = hosts.remove(hostId);
+            if (host != null) {
+                locations.remove((host.location()), host);
+                removedHosts.put(hostId, new Timestamped<>(host, timestamp));
+                return new HostEvent(HOST_REMOVED, host);
+            }
+            return null;
+        }
+    }
+
+    @Override
+    public int getHostCount() {
+        return hosts.size();
+    }
+
+    @Override
+    public Iterable<Host> getHosts() {
+        return ImmutableSet.<Host>copyOf(hosts.values());
+    }
+
+    @Override
+    public Host getHost(HostId hostId) {
+        return hosts.get(hostId);
+    }
+
+    @Override
+    public Set<Host> getHosts(VlanId vlanId) {
+        Set<Host> vlanset = new HashSet<>();
+        for (Host h : hosts.values()) {
+            if (h.vlan().equals(vlanId)) {
+                vlanset.add(h);
+            }
+        }
+        return vlanset;
+    }
+
+    @Override
+    public Set<Host> getHosts(MacAddress mac) {
+        Set<Host> macset = new HashSet<>();
+        for (Host h : hosts.values()) {
+            if (h.mac().equals(mac)) {
+                macset.add(h);
+            }
+        }
+        return macset;
+    }
+
+    @Override
+    public Set<Host> getHosts(IpPrefix ip) {
+        Set<Host> ipset = new HashSet<>();
+        for (Host h : hosts.values()) {
+            if (h.ipAddresses().contains(ip)) {
+                ipset.add(h);
+            }
+        }
+        return ipset;
+    }
+
+    @Override
+    public Set<Host> getConnectedHosts(ConnectPoint connectPoint) {
+        return ImmutableSet.copyOf(locations.get(connectPoint));
+    }
+
+    @Override
+    public Set<Host> getConnectedHosts(DeviceId deviceId) {
+        Set<Host> hostset = new HashSet<>();
+        for (ConnectPoint p : locations.keySet()) {
+            if (p.deviceId().equals(deviceId)) {
+                hostset.addAll(locations.get(p));
+            }
+        }
+        return hostset;
+    }
+
+    @Override
+    public void updateAddressBindings(PortAddresses addresses) {
+        synchronized (portAddresses) {
+            PortAddresses existing = portAddresses.get(addresses.connectPoint());
+            if (existing == null) {
+                portAddresses.put(addresses.connectPoint(), addresses);
+            } else {
+                Set<IpPrefix> union = Sets.union(existing.ips(), addresses.ips())
+                        .immutableCopy();
+
+                MacAddress newMac = (addresses.mac() == null) ? existing.mac()
+                        : addresses.mac();
+
+                PortAddresses newAddresses =
+                        new PortAddresses(addresses.connectPoint(), union, newMac);
+
+                portAddresses.put(newAddresses.connectPoint(), newAddresses);
+            }
+        }
+    }
+
+    @Override
+    public void removeAddressBindings(PortAddresses addresses) {
+        synchronized (portAddresses) {
+            PortAddresses existing = portAddresses.get(addresses.connectPoint());
+            if (existing != null) {
+                Set<IpPrefix> difference =
+                        Sets.difference(existing.ips(), addresses.ips()).immutableCopy();
+
+                // If they removed the existing mac, set the new mac to null.
+                // Otherwise, keep the existing mac.
+                MacAddress newMac = existing.mac();
+                if (addresses.mac() != null && addresses.mac().equals(existing.mac())) {
+                    newMac = null;
+                }
+
+                PortAddresses newAddresses =
+                        new PortAddresses(addresses.connectPoint(), difference, newMac);
+
+                portAddresses.put(newAddresses.connectPoint(), newAddresses);
+            }
+        }
+    }
+
+    @Override
+    public void clearAddressBindings(ConnectPoint connectPoint) {
+        synchronized (portAddresses) {
+            portAddresses.remove(connectPoint);
+        }
+    }
+
+    @Override
+    public Set<PortAddresses> getAddressBindings() {
+        synchronized (portAddresses) {
+            return new HashSet<>(portAddresses.values());
+        }
+    }
+
+    @Override
+    public PortAddresses getAddressBindingsForPort(ConnectPoint connectPoint) {
+        PortAddresses addresses;
+
+        synchronized (portAddresses) {
+            addresses = portAddresses.get(connectPoint);
+        }
+
+        if (addresses == null) {
+            addresses = new PortAddresses(connectPoint, null, null);
+        }
+
+        return addresses;
+    }
+
+    // Auxiliary extension to allow location to mutate.
+    private class StoredHost extends DefaultHost {
+        private Timestamped<HostLocation> location;
+
+        /**
+         * Creates an end-station host using the supplied information.
+         *
+         * @param providerId  provider identity
+         * @param id          host identifier
+         * @param mac         host MAC address
+         * @param vlan        host VLAN identifier
+         * @param location    host location
+         * @param ips         host IP addresses
+         * @param annotations optional key/value annotations
+         */
+        public StoredHost(ProviderId providerId, HostId id,
+                          MacAddress mac, VlanId vlan, Timestamped<HostLocation> location,
+                          Set<IpPrefix> ips, Annotations... annotations) {
+            super(providerId, id, mac, vlan, location.value(), ips, annotations);
+            this.location = location;
+        }
+
+        void setLocation(Timestamped<HostLocation> location) {
+            this.location = location;
+        }
+
+        @Override
+        public HostLocation location() {
+            return location.value();
+        }
+    }
+}