how to Create "Keep Alive" for a chat app?

At the moment im doing a chat web app where multiple users can chat and it can control multiple rooms. Its working and getting the job done.

Right now its using ajax(jquery is used) and just use GET to the server.aspx with different query parameters and then return some content.(It is meant to be build into a larger project later on)

But I have one thing that I cannot figure out how to build for it and hopin' someone had a splendid idea :)

A "Keep Alive" (or TimeToLive) service on the users. The service should ensure when a user disconnects(machine crash - Browser/window close) the user times out from the chat room.

My idea was that on every request from the user TO the server it should update a TTL list(a list with a userid and a "timestamp") and this part is easy.

Now comes my challenge

Then there should be some service running on the server that continuesly checks this TTL list to see if any stamps has run out and if it has remove the user from the room

But how and where can I do this server service in .net ? Or do you have another approch ? :)

I would just have a table called something like "LastPing" with user id and a date. Put a piece of javascript which calls a page on your site at regular intervals (window.setInterval(...)) - that page just updates the table with the current datetime or does an insert if no rows are updated.

Finally, create a sql server job/task that selects user id from Lastping where date is older than currentdate - 30 mins (or whatever). Those user ids get deleted from any chat rooms etc. and finally removed from the LastPing table.

I think that's about it :)

You could run a Console Application (or run it as a Windows Service) that could scan your TTL list using a Timer that ticks on a set interval to process them as you wish. Could all be done in .net, preventing you from having to store your business logic in an SSIS package within SQL server.

If you're going down this path I would recommend writing a windows service that can also be run as a console app. Query the Environment.UserInteractive property to work out which version is being run - this will help with your development because a console application can be a little more verbose than a windows service.

Here is a code sample:

public partial class Service1 : ServiceBase
{
    //Need to keep a reference to this object, else the Garbage Collector will clean it up and prevent further events from firing.
    private System.Threading.Timer _timer;

    static void Main(string[] args)
    {
        if (Environment.UserInteractive)
        {
            var service = new Service1();
            Log.Debug("Starting Console Application");

            service.OnStart(args);
            // The service can now be accessed.
            Console.WriteLine("Service ready.");
            Console.WriteLine("Press <ENTER> to terminate the application.");
            Console.ReadLine();
            service.OnStop();

            return;
        }
        var servicesToRun = new ServiceBase[] 
                                          { 
                                              new Service1() 
                                          };
        Run(servicesToRun);
    }

    public Service1()
    {
        InitializeComponent();
    }

    protected override void OnStart(string[] args)
    {
        // For a single instance, this is a bit heavy handed, but if you're creating of a number of them
        // the NT service will need to return in a short period of time and thus I use QueueUserWorkItem
        ThreadPool.QueueUserWorkItem(SetupTimer, args);
    }

    protected override void OnStop()
    {
    }

    private void SetupTimer(object obj)
    {


        //Set the emailInterval to be 1 minute by default
        const int interval = 1;
        //Initialize the timer, wait 5 seconds before firing, and then fire every 15 minutes
        _timer = new Timer(TimerDelegate, 5000, 1, 1000 * 60 * interval);
    }
    private static void TimerDelegate(object stateInfo)
    {
            //Perform your DB TTL Check here
    }

}

For that type of solution, you would need to setup a separate Thread that is periodically checking for users to expire, or utilize a library for scheduled tasks and similarly setup a scheduled task.