How to solve a while true loop as it is expensive and Risky

Question

I make an AJAX request to see if a sesion variable has been set. I make a GET request to this script:

<?php session_start();

while(true){
    if(isset($_SESSION['screen_name'])){
        return true;
        break;
    }
}

?>

Clearly there are problems with this script and I wanted to solve these problems such as the continuous checking and waste of resources.

Scenario: I am trying to implement the oAuth method that twitgoo have used. You click "sign in" and then a window pops up for you to sign in to twitter. If you are successful, twitter redirects to a call back URL (which I guess sets session info) and the window is closed. Once this is done your message is posted to twitter. I am trying to achieve this and I am nearly there but I am unsure of my script above.

I would appreciate any help in making this script not so wasteful and if you have a better implementation, I would love to hear it.

Thanks all

Update

I have been give two good options which do you think is more efficient between:

1) Polling the server every few seconds using JS instead of the while loop eating up CPU cycles

2) Keep the while loop but "ease up" on the level of checking meaning no more http requests will be wasted

Answer 1

This is a PHP script? Is there any condition that may change the state of $_SESSION['screen_name'] other than a page refresh/new poll, i.e. a restart of the script in the first place?

The $_SESSION variable depends on the request. It's not going to change while the script runs, unless changed by the script. All this script does is either return true if the condition is met, or loop until the timeout is hit. The condition is either true on the first try or never will be.

Answer 2

Unfortunately, all you've created here is an infinite loop. If $_SESSION['screen_name'] isn't set the first time through, it's never, ever going to be set. Once you've loaded a PHP script, the environment variables will not change. You will never receive another session cookie, nor will any of $_GET, $_POST, $_SESSION, etc. ever be modified, unless you do it explicitly inside the script, or the script ends and you make another request.

My suggestion here would be something like this:

if(isset($_SESSION['screen_name'])){
    return true;
    break;
}
else {
  //output JSON encoded error message
}

If you exit your script when the required session variable isn't set and send a response back to the browser, then the browser can decide what to do. Perhaps make another request, maybe wait ten seconds, maybe load a login dialog.

Answer 3

I may be saying something really stupid here, but wouldn't you be better off just taking out the while loop and leaving the polling up to javascript?

Answer 4

store your result in memcache, then use the while loop with usleep() between iterations checking memcache for the variable.

This will allow you to do essentially a long poll instead of having to chain a bunch of xmlhttprequests waiting for the result.

Answer 5

How about this:

screen_name_check.php

<?php session_start();
if (isset($_SESSION['screen_name']))
    return "1";
return "0";
?>

page.html

<script type="text/javascript">
    check_screen_name_interval = window.setIterval(function(){
        // AJAX call screen_name_check.php
        if (data=="1") {
        window.clearInterval(check_screen_name_interval);
        // do whatever JS needs with that session set
        // or AJAX call a different PHP page like screen_name_is_set.php
        }
    }, 2000);
</script>