+1  A: 

Unfortunately, there is no solid way of doing such clean up functions that execute asynchronously. The result/fault events of the HTTPService occur asynchronously after the cleanUp method is returned. The browser waits only till the onbeforeunload function (the js *clean_up* function) returns. Unless you call event.preventDefault() from that function, the page will be closed. Note that calling preventDefault() will result in an ok/cancel popup asking:

Are you sure you want to navigate away from this page?

Press OK to continue, or Cancel to stay on the current page.

If the user selects OK, the browser will be closed nevertheless. You can use the event.returnValue property to add a custom message to the popop.

//tested only in Firefox
window.addEventListener("beforeunload", onUnload, false);
function onUnload(e)
{
   e.returnValue = "Some text that you want inserted between " +
     "'Are you sure' and 'Press OK' lines";
   e.preventDefault();
}
Amarghosh
so, there is no way to ensure that the cleanup is finished, because there is no way to prevent the user to select 'ok'??
tomato
+1  A: 

You'll never be able to reliably detect the browser code 100% of the time. If you really need to run actions then the safest course of action is to have clients send "i'm still alive" messages to the server. The server needs to track time by client and when a client doesn't send a message within the specified amount of time (with some wiggle room), then run clean-up activities.

The longer you make the time the better, it depends on how time-critical the clean-up is. If you can get away with waiting 5 minutes that's great, otherwise look at 1 minute or 30 seconds or whatever is required for your app.

Sam
thanks for the answer. this is a different approach to the problem, will keep this in mind...
tomato
+1  A: 

an alternate way to clean up the session on client side is to use javascript and external.interface class in as3. here is a sample code:

java script:

function cleanUp() {

var process;
var swfID="customRightClick";
if(navigator.appName.indexOf("Microsoft") != -1){
    process = window[swfID];
    }else
{
    process = document[swfID];
}
process.cleanUp();

}

and in the as3 class where the clean up function is defined use this :

import flash.external.ExternalInterface;

if (ExternalInterface.available) { ExternalInterface.addCallback("cleanUp", cleanUp); }

function cleanUp():void {// your code }

I hope it works for you too.

intoTHEwild
This is a nice way of cleaning up the session on client-side. Thanks. :) Unfortunately, it doesn't apply to my case, because I'm trying to trigger something on the server-side through HTTP request, when the user closes the browser. I could do it this way, but the key to my problem is still how to ensure my HTTP request has completed by the time the browser shuts down.
tomato