Synchronize.Messenger.Notify C# (CSharp) Method

        public void Notify(FriendRequest user)
        {
            FriendRequestRecieved(this, user);
        }
    }

        private static void MultipleObservableSynchronization()
        {
            Demo.DisplayHeader("The Synchrnoize operator - can synchronizes the notifications from multiple observables by passing the gate object");

            var messenger = new Messenger();
            var messages  =
                Observable.FromEventPattern <string>(
                    h => messenger.MessageRecieved += h,
                    h => messenger.MessageRecieved -= h);

            var friendRequests =
                Observable.FromEventPattern <FriendRequest>(
                    h => messenger.FriendRequestRecieved += h,
                    h => messenger.FriendRequestRecieved -= h);

            var gate = new object();

            messages
            .Select(evt => evt.EventArgs)
            .Synchronize(gate)
            .Subscribe(msg =>
            {
                Console.WriteLine("Message {0} arrived", msg);
                Thread.Sleep(1000);
                Console.WriteLine("Message {0} exit", msg);
            });


            friendRequests
            .Select(evt => evt.EventArgs)
            .Synchronize(gate)
            .Subscribe(request =>
            {
                Console.WriteLine("user {0} sent request", request.UserId);
                Thread.Sleep(1000);
                Console.WriteLine("user {0} approved", request.UserId);
            });
            for (int i = 0; i < 3; i++)
            {
                string msg    = "msg" + i;
                string userId = "user" + i;
                ThreadPool.QueueUserWorkItem((_) =>
                {
                    messenger.Notify(msg);
                });

                ThreadPool.QueueUserWorkItem((_) =>
                {
                    messenger.Notify(new FriendRequest()
                    {
                        UserId = userId
                    });
                });
            }

            //waiting for all the other threads to complete before proceeding
            Thread.Sleep(3000);
        }