Client Server Event Subscription Techniques in C#

/// Author - anshu.dutta@gmail.com ///
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace Demo.Events.Observer
{
    class Program
    {
        static void Main(string[] args)
        {
            Server s = new Server()
            {
                Clients= new List<IObserver>()
                {
                    new Client(){ClientId=1},
                    new Client(){ClientId=2},
                    new Client(){ClientId=3}
                }
            };
            

            while (true)
            {
                Thread.Sleep(new Random().Next(10) * 1000);
                Console.WriteLine("Server Generating event {0}", DateTime.Now.ToString("hh:mm:ss"));
                s.Notify();
            }
        }
    }

    public interface ISubject
    {
        
        void Add(IObserver Observer);
        void Remove(IObserver observer);
        void Notify();
    }

    public class Server : ISubject
    {
        public List<IObserver> Clients { get; set; }

        public Server()
        {
            Clients = new List<IObserver>();
        }        

        public void Add(IObserver Observer)
        {
            if (Clients != null)
                Clients.Add(Observer);
        }

        public void Remove(IObserver observer)
        {
            if (Clients != null)
                Clients.Remove(observer);
        }

        public void Notify()
        {
            //foreach (IObserver item in Clients)
            //{
            //    item.Update();
            //};
            Parallel.ForEach<IObserver>(Clients, item =>
                {
                    item.Update();
                });            
        }        
    }

    public interface IObserver
    {
        void Update();
    }

    public class Client : IObserver
    {
        public Client(){}

        public int ClientId {get;set;}

        public void Update()
        {
            Console.WriteLine("Event received from server by client {0} @ {1}", ClientId, DateTime.Now.ToString("hh:mm:ss"));
            //Do work
            ProcessEvent();
            Console.WriteLine("Event processed by client {0} @ {1}", ClientId, DateTime.Now.ToString("hh:mm:ss"));
        }

        void ProcessEvent()
        {
            System.Threading.Thread.Sleep(2000);
        }
    }
}