Chg: #85 - move message delivery notification into Topology.notifyMessageDelivered(Message) + protect list from concurrent access

Author: remikey

lib/jbotsim-core/src/main/java/io/jbotsim/core/DefaultMessageEngine.java

@@ -219,8 +219,7 @@ protected void deliverMessages(Collection<Message> messagesToSend) {
     protected void deliverMessage(Message message) {
         message.getDestination().getMailbox().add(message);
         message.getDestination().onMessage(message);
-        for (MessageListener ml : topology.messageListeners)
-            ml.onMessage(message);
+        topology.notifyMessageDelivered(message);
         if (debug)
             System.err.println(topology.getTime() + ": " + message);
     }

lib/jbotsim-core/src/main/java/io/jbotsim/core/Topology.java

@@ -1113,6 +1113,11 @@ protected void notifyNodeSelected(Node node) {
             tl.onSelection(node);
     }
 
+    protected void notifyMessageDelivered(Message message) {
+        for (MessageListener listener : new ArrayList<>(messageListeners))
+            listener.onMessage(message);
+    }
+
     @Override
     public void onClock() {
         if (step) {