Fixed bug in LocationRequests

- if a request is re-used within a given time frame (<= the update
interval), this leads to incorrect event duplication and, thus, too
frequent listener calls

src/de/tud/kom/p2psim/impl/topology/DefaultTopologyComponent.java

@@ -45,6 +45,7 @@ import de.tudarmstadt.maki.simonstrator.api.Graphs;
 import de.tudarmstadt.maki.simonstrator.api.Host;
 import de.tudarmstadt.maki.simonstrator.api.Oracle;
 import de.tudarmstadt.maki.simonstrator.api.Randoms;
+import de.tudarmstadt.maki.simonstrator.api.Time;
 import de.tudarmstadt.maki.simonstrator.api.common.graph.Graph;
 import de.tudarmstadt.maki.simonstrator.api.common.graph.IEdge;
 import de.tudarmstadt.maki.simonstrator.api.common.graph.INode;
@@ -317,6 +318,8 @@ public class DefaultTopologyComponent implements TopologyComponent {
 		private Location lastLocation = null;
 
 		private List<LocationListener> listeners = new LinkedList<LocationListener>();
+		
+		private int eventTypeSeq = 0;
 
 		public LocationRequestImpl() {
 			// nothing to do
@@ -324,6 +327,10 @@ public class DefaultTopologyComponent implements TopologyComponent {
 
 		protected void cancel(LocationListener listener) {
 			boolean removed = listeners.remove(listener);
+			if (listeners.isEmpty()) {
+				// upcoming event is no longer valid!
+				eventTypeSeq++;
+			}
 			assert removed;
 		}
 
@@ -333,7 +340,7 @@ public class DefaultTopologyComponent implements TopologyComponent {
 			if (listeners.isEmpty()) {
 				// Only start once!
 				lastLocation = null;
-				Event.scheduleImmediately(this, null, 0);
+				Event.scheduleImmediately(this, null, eventTypeSeq);
 			} else {
 				// Fire each new listener at least once
 				listener.onLocationChanged(getHost(), getLastLocation());
@@ -357,13 +364,22 @@ public class DefaultTopologyComponent implements TopologyComponent {
 
 		@Override
 		public void eventOccurred(Object content, int type) {
+			if (eventTypeSeq != type) {
+				/*
+				 * Discard invalid events caused when a client cancels updates 
+				 * but reactivates the request within the update frequency 
+				 * interval. In this case, the old events continue rescheduling 
+				 * themselves.
+				 */
+				return;
+			}
 			if (!listeners.isEmpty()) {
 				// Only reschedule, if at least one listener is ... listening
 				Location newLoc = getLastLocation();
 				listeners.forEach((LocationListener listener) -> listener
 							.onLocationChanged(getHost(), newLoc));
 				lastLocation = newLoc;
-				Event.scheduleWithDelay(interval, this, null, 0);
+				Event.scheduleWithDelay(interval, this, null, eventTypeSeq);
 			}
 		}