Question

I have the following HttpHandler; I’m using it to push updates to the browser (where jQuery and GrowlUI are implemented) without the need for the browser to poll. I think all I’ve accomplished is moving the polling loop to the server.

Can anyone tell me how I can make this class more robust and scalable?

Here is the code.

public class LiveUpdates : IHttpHandler
{
    //TODO: Replace this with a repository that the application can log to.
    private static readonly Dictionary<string, Queue<string>> updateQueue;
    static LiveUpdates()
    {
        updateQueue = new Dictionary<string, Queue<string>>();
    }

    public void ProcessRequest(HttpContext context)
    {
        context.Response.Buffer = true;

        while (context.Response.IsClientConnected)
        {
            if (context.User == null) return;
            if (!context.User.Identity.IsAuthenticated) return;

            Thread.Sleep(1000);
            if (!updateQueue.ContainsKey(context.User.Identity.Name)) continue;
            if (updateQueue[context.User.Identity.Name].Count == 0) continue;

            GrowlStatus(context.Response, updateQueue[context.User.Identity.Name].Dequeue());
        }


    }

    protected static void GrowlStatus(HttpResponse Response, string Message)
    {
        // Write out the parent script callback.
        Response.Write(String.Format("<script type=\"text/javascript\">parent.$.growlUI('Message', '{0}');</script>", Message));
        // To be sure the response isn't buffered on the server.    
        Response.Flush();
    }

    public static void QueueUpdate(IPrincipal User, string UpdateMessage)
    {
        if (!updateQueue.ContainsKey(User.Identity.Name))
        {
            updateQueue.Add(User.Identity.Name, new Queue<string>());
        }
        updateQueue[User.Identity.Name].Enqueue(UpdateMessage);
    }

    public static void ClearUpdates(IPrincipal User)
    {
        if (updateQueue.ContainsKey(User.Identity.Name)) updateQueue.Remove(User.Identity.Name);
    }

Answer 1

If you plan to use Thread.Sleep(), you MUST implement System.Web.IHttpAsyncHandler or your handler will not scale.