[ONOS-3117] adding listener to Port-Pair-Group Manager

Change-Id: I33dcdc6172e4a5a596d0e376e224ee3eb42387cd

@@ -77,4 +77,18 @@ public interface PortPairGroupService {
      * @return true if the give port pair group is deleted successfully.
      */
     boolean removePortPairGroup(PortPairGroupId portPairGroupId);
+
+    /**
+     * Adds the specified listener to Port-Pair-Group manager.
+     *
+     * @param listener Port-Pair-Group listener
+     */
+    void addListener(PortPairGroupListener listener);
+
+    /**
+     * Removes the specified listener to Port-Pair-Group manager.
+     *
+     * @param listener Port-Pair-Group listener
+     */
+    void removeListener(PortPairGroupListener listener);
 }

@@ -19,6 +19,7 @@ import static com.google.common.base.Preconditions.checkNotNull;
 import static org.slf4j.LoggerFactory.getLogger;
 
 import java.util.Collections;
+import java.util.Set;
 
 import org.apache.felix.scr.annotations.Activate;
 import org.apache.felix.scr.annotations.Component;
@@ -34,9 +35,12 @@ import org.onosproject.store.service.StorageService;
 import org.onosproject.store.service.WallClockTimestamp;
 import org.onosproject.vtnrsc.PortPairGroup;
 import org.onosproject.vtnrsc.PortPairGroupId;
+import org.onosproject.vtnrsc.portpairgroup.PortPairGroupListener;
 import org.onosproject.vtnrsc.portpairgroup.PortPairGroupService;
 import org.slf4j.Logger;
 
+import com.google.common.collect.Sets;
+
 /**
  * Provides implementation of the portPairGroupService.
  */
@@ -44,11 +48,12 @@ import org.slf4j.Logger;
 @Service
 public class PortPairGroupManager implements PortPairGroupService {
 
-    private final Logger log = getLogger(getClass());
-
     private static final String PORT_PAIR_GROUP_ID_NULL = "PortPairGroup ID cannot be null";
     private static final String PORT_PAIR_GROUP_NULL = "PortPairGroup cannot be null";
+    private static final String LISTENER_NOT_NULL = "Listener cannot be null";
 
+    private final Logger log = getLogger(getClass());
+    private final Set<PortPairGroupListener> listeners = Sets.newCopyOnWriteArraySet();
     private EventuallyConsistentMap<PortPairGroupId, PortPairGroup> portPairGroupStore;
 
     @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
@@ -73,6 +78,7 @@ public class PortPairGroupManager implements PortPairGroupService {
     @Deactivate
     public void deactivate() {
         portPairGroupStore.destroy();
+        listeners.clear();
         log.info("Stopped");
     }
 
@@ -143,4 +149,16 @@ public class PortPairGroupManager implements PortPairGroupService {
         }
         return true;
     }
+
+    @Override
+    public void addListener(PortPairGroupListener listener) {
+        checkNotNull(listener, LISTENER_NOT_NULL);
+        listeners.add(listener);
+    }
+
+    @Override
+    public void removeListener(PortPairGroupListener listener) {
+        checkNotNull(listener, LISTENER_NOT_NULL);
+        listeners.remove(listener);
+    }
 }