code: public synchronized int addSubscriber(String eventName, IGenericEvent<T> subscriber) {
          List<IGenericEvent<T>> subscribers = getSubscribers(eventName, true);
          subscribers.add(subscriber);
          return subscribers.size();
      }
docs: Adds a subscriber to the specified event.
  
  @param eventName Name of the event.
  @param subscriber Subscriber to add.
  @return Count of subscribers after the operation.