Corrected behavior of PortListener (not critical)

src/de/tud/kom/p2psim/impl/transport/modular/ModularTransLayer.java

@@ -240,6 +240,8 @@ public class ModularTransLayer implements SimHostComponent, TransportComponent,
 		private final int localPort;
 
 		private final ITransProtocol transport;
+		
+		private TransMessageListener listener;
 
 		public ProtocolAdapter(NetID localAddress, int localPort,
 				ITransProtocol transport) {
@@ -250,6 +252,7 @@ public class ModularTransLayer implements SimHostComponent, TransportComponent,
 
 		@Override
 		public void setTransportMessageListener(TransMessageListener listener) {
+			this.listener = listener;
 			addTransMsgListener(listener, localPort);
 		}
 
@@ -257,7 +260,9 @@ public class ModularTransLayer implements SimHostComponent, TransportComponent,
 		 * FIXME add @Override lateron, as soon as the API is updated globally.
 		 */
 		public void removeTransportMessageListener() {
-			removeTransMsgListener(localPort);
+			assert listener != null;
+			removeTransMsgListener(listener, localPort);
+			listener = null;
 		}
 
 		@Override
@@ -403,9 +408,12 @@ public class ModularTransLayer implements SimHostComponent, TransportComponent,
 		pl.addListener(receiver);
 	}
 
-	protected void removeTransMsgListener(int port) {
-		// assuming there is only one
-		portListeners.remove(port);
+	protected void removeTransMsgListener(TransMessageListener listener, int port) {
+		PortListener pl = portListeners.get(port);
+		pl.removeListener(listener);
+		if (pl.isEmpty()) {
+			portListeners.remove(port);
+		}
 	}
 
 	@Override
@@ -527,9 +535,8 @@ public class ModularTransLayer implements SimHostComponent, TransportComponent,
 	}
 
 	/**
-	 * A very simple data structure to allow multiple Listeners on one port
-	 * 
-	 * FIXME why would we need to support more than one listener per port?
+	 * A very simple data structure to allow multiple Listeners on one port (e.g., if TCP and UDP are 
+	 * both instantiated on the same port)
 	 * 
 	 * @author Bjoern Richerzhagen
 	 * @version 1.0, 07.05.2012