ASP.NET MVC3 : Connected clients count - asp.net

Question

In my ASP.NET MVC3 web application I'd like to add a small message displaying the number of users currently browsing the site.
I'm currently using Session_Start and Session_End application events to increment or decrement a static property inside Global.asax.
This works, but it isn't precise at all. Since my session timeout is configured to 20mn there's a huge delay between updates.
Is there a more elegant, precise way of doing this?
I've thought of calling an action via AJAX which simply does Session.Abandon() on the window.onbeforeunload javascript event, but this would be called each time the user changed pages. Is there a way to determine when the user closes his browser or leaves the domain?
Any hints, comments or code examples would be welcome!
Here is the relevant part of current code:
public class MvcApplication : System.Web.HttpApplication
{
public static int UsersConnected { get; set; }
protected void Session_Start(object sender, EventArgs e)
{
Application.Lock();
UsersConnected++;
Application.UnLock();
}
protected void Session_End(object sender, EventArgs e)
{
Application.Lock();
UsersConnected--;
Application.UnLock();
}
...
}

Answer 1

Okay this was a bit tricky but I've come with an 'okay' solution.
First, Ive created a static dictionary in Global.asax which will store the IP address of the clients and their last poll date.
public class MvcApplication : System.Web.HttpApplication
{
public static Dictionary<string, DateTime> ConnectedtUsers { get; set; }
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
RegisterGlobalFilters(GlobalFilters.Filters);
RegisterRoutes(RouteTable.Routes);
ConnectedtUsers = new Dictionary<string, DateTime>();
}
...
}
Then, in my CommonsController, I've created this action which will add new clients, remove clients which haven't been polled in the last 30 seconds and update the poll date of already registered clients :
public class CommonsController : Controller
{
...
public JsonResult UserConnected()
{
string ip = Request.UserHostAddress;
if (MvcApplication.ConnectedtUsers.ContainsKey(ip))
{
MvcApplication.ConnectedtUsers[ip] = DateTime.Now;
}
else
{
MvcApplication.ConnectedtUsers.Add(ip, DateTime.Now);
}
int connected = MvcApplication.ConnectedtUsers.Where(c => c.Value.AddSeconds(30d) > DateTime.Now).Count();
foreach (string key in MvcApplication.ConnectedtUsers.Where(c => c.Value.AddSeconds(30d) < DateTime.Now).Select(c => c.Key))
{
MvcApplication.ConnectedtUsers.Remove(key);
}
return Json(new { count = connected }, JsonRequestBehavior.AllowGet);
}
}
Finally, on my layout page, added this code which will call my action every 30 seconds and output the result in a span :
<span id="connectedUsers"></span>
<script type="text/javascript">
function PollUsers()
{
$(function() {
$.getJSON("/Commons/UserConnected", function(json){ $('#connectedUsers').text(json.count + " user(s) connected")});
});
}
setInterval(PollUsers, 30000);
</script>
May not be that precise, maybe not that elegant either, but it works. Of course, multiple users from the same IP would count for one user. But it's the best solution I've experimented so far.

Answer 2

you can call a webmethod from javascript on unload body event.
http://www.codeproject.com/Tips/89661/Execute-server-side-code-on-close-of-a-browser
Best regards