Silverlight 4 with (HTTP) Duplex and SQL Notifications

using System;
using System.Collections.Generic;
using System.Linq;
using System.ServiceModel;
using System.Web;
using SLDuplexDependency.Web.Classes;

namespace SLDuplexDependency.Web.DBNotificationService
{
	/// <summary>
	/// This is an implementation of IDBNotificationService interface
	/// </summary>
	[ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Multiple, InstanceContextMode = InstanceContextMode.Single)]
	public class DBNotificationService : IDBNotificationService 
	{
		/// <summary>
		/// The object used to lock code down when it is editing static data
		/// </summary>
		private Object syncRoot = new Object();		

		/// <summary>
		/// This method should be executed to subscribe to notifications from server.
		/// </summary>
		public void SubscribeToNotifications()
		{
			IDBNotificationCallbackContract ch = OperationContext.Current.GetCallbackChannel<IDBNotificationCallbackContract>();
			string sessionId = OperationContext.Current.Channel.SessionId;

			//Any message from a client we haven't seen before causes the new client to be added to our list			
			lock (syncRoot)
			{
				if (!SilverlightClientsList.IsClientConnected(sessionId))
				{
					SilverlightClientsList.AddCallbackChannel(sessionId, ch);
					OperationContext.Current.Channel.Closing += new EventHandler(Channel_Closing);
					OperationContext.Current.Channel.Faulted += new EventHandler(Channel_Faulted);
				}
			}
		}

		/// <summary>
		/// Handles the Closing event of the Channel control.
		/// </summary>
		/// <param name="sender">The source of the event.</param>
		/// <param name="e">The <see cref="System.EventArgs"/> instance containing the event data.</param>
		private void Channel_Closing(object sender, EventArgs e)
		{
			IContextChannel channel = (IContextChannel)sender;
			ClientDisconnect(channel.SessionId);
		}

		/// <summary>
		/// Handles the Faulted event of the Channel control.
		/// </summary>
		/// <param name="sender">The source of the event.</param>
		/// <param name="e">The <see cref="System.EventArgs"/> instance containing the event data.</param>
		private void Channel_Faulted(object sender, EventArgs e)
		{
			IContextChannel channel = (IContextChannel)sender;
			ClientDisconnect(channel.SessionId);
		}

		/// <summary>
        /// Disconnect the client.
		/// </summary>
		/// <param name="sessionId">The session id.</param>
		private void ClientDisconnect(string sessionId)
		{
			lock (syncRoot)
			{
				if (SilverlightClientsList.IsClientConnected(sessionId))
					SilverlightClientsList.DeleteClient(sessionId);
			}
		}

		/// <summary>
		/// This method should be executed to unsubscribe to notifications from server.
		/// </summary>
		public void UnsubscribeToNotifications()
		{
			ClientDisconnect(OperationContext.Current.Channel.SessionId);
		}		
	}
}