gistfile1.cs

            private ConcurrentDictionary<Type, ConcurrentBag<ISubscription>> listeners =
                new ConcurrentDictionary<Type, ConcurrentBag<ISubscription>>();
                
            public void Publish<T>(T message) where T : class, IMessage
        {
            if (!listeners.ContainsKey(typeof(T)))
            {
                return;
            }

            foreach (INotificationHandler<T> handler in listeners[typeof(T)])
            {
                handler.ProcessMessage(message);
            }
        }