Prevent Duplicate Queue Subscription

event/eventmanager.go

@@ -95,6 +95,11 @@ func (em *manager) initialize() {
 func (em *manager) Subscribe(eventType Type, queue Queue) {
 	em.mapMutex.Lock()
 	defer em.mapMutex.Unlock()
+	for _, sub := range em.subscribers[eventType] {
+		if sub == queue {
+			return // don't add the same queue for the same event twice...
+		}
+	}
 	em.subscribers[eventType] = append(em.subscribers[eventType], queue)
 }