Fixed objective tracker not to do extra work so eagerly.

Added ability to see availability status as part of device events (for availability events)

Change-Id: I4a3476e203459ed72deee45f0a24e4b4373bd819

@@ -20,7 +20,10 @@ import org.onosproject.event.AbstractEvent;
 import org.onosproject.net.Device;
 import org.onosproject.net.Port;
 
+import java.util.Optional;
+
 import static com.google.common.base.MoreObjects.toStringHelper;
+import static org.onosproject.net.device.DeviceEvent.Type.DEVICE_AVAILABILITY_CHANGED;
 
 /**
  * Describes infrastructure device event.
@@ -28,6 +31,7 @@ import static com.google.common.base.MoreObjects.toStringHelper;
 public class DeviceEvent extends AbstractEvent<DeviceEvent.Type, Device> {
 
     private final Port port;
+    private final boolean isAvailable;
 
     /**
      * Type of device events.
@@ -102,6 +106,20 @@ public class DeviceEvent extends AbstractEvent<DeviceEvent.Type, Device> {
     public DeviceEvent(Type type, Device device, Port port) {
         super(type, device);
         this.port = port;
+        this.isAvailable = false;
+    }
+
+    /**
+     * Creates an event for change of device availability for the given device
+     * and the current time.
+     *
+     * @param device      event device subject
+     * @param isAvailable true if device became available; false otherwise
+     */
+    public DeviceEvent(Device device, boolean isAvailable) {
+        super(DEVICE_AVAILABILITY_CHANGED, device);
+        this.port = null;
+        this.isAvailable = isAvailable;
     }
 
     /**
@@ -115,6 +133,7 @@ public class DeviceEvent extends AbstractEvent<DeviceEvent.Type, Device> {
     public DeviceEvent(Type type, Device device, Port port, long time) {
         super(type, device, time);
         this.port = port;
+        this.isAvailable = false;
     }
 
     /**
@@ -126,6 +145,15 @@ public class DeviceEvent extends AbstractEvent<DeviceEvent.Type, Device> {
         return port;
     }
 
+    /**
+     * Indicates whether device became available or unavailable.
+     *
+     * @return if present, true indicates device came online; false if device went offline
+     */
+    public Optional<Boolean> isAvailable() {
+        return type() == DEVICE_AVAILABILITY_CHANGED ? Optional.of(isAvailable) : Optional.empty();
+    }
+
     @Override
     public String toString() {
         if (port == null) {

@@ -444,7 +444,7 @@ public class GossipDeviceStore
             boolean wasOnline = availableDevices.contains(newDevice.id());
             markOnline(newDevice.id(), newTimestamp);
             if (!wasOnline) {
-                notifyDelegateIfNotNull(new DeviceEvent(DEVICE_AVAILABILITY_CHANGED, newDevice, null));
+                notifyDelegateIfNotNull(new DeviceEvent(newDevice, true));
             }
         }
         return event;
@@ -487,7 +487,7 @@ public class GossipDeviceStore
             }
             boolean removed = availableDevices.remove(deviceId);
             if (removed) {
-                return new DeviceEvent(DEVICE_AVAILABILITY_CHANGED, device, null);
+                return new DeviceEvent(device, false);
             }
             return null;
         }