AJAX launched PHP script terminating without good reason

Question

I have a very simple PHP script:

ini_set('max_execution_time', 240000);

//Switch for terminating the test processing status loop
$completed = false; 

while ($completed == false) {
    sleep(2);
}

This is launched using AJAX which is again, very simple:

$.ajax({
    url: "lib/check_processing_status.php",
    timeout: 0,
    async: true,
    error: function() {
        console.log("FAILURE");
    },
    success: function() {
        console.log("SUCCESS");
    }
});

This script should run indefinitely, or at least until the timeout is triggered. Yet it fails after a duration which differs each time it is run. Sometimes just 40 seconds, sometimes 1 minute and 10 seconds.

Why is this failing!?

Additional:

Just to add some context, the reason I am having a loop like this, is because I will be querying a server for the progress of a process, so instead of calling loads of AJAX requests every 5 seconds (filling up the console window with 10's of requests), I figured it neater to stay inside the PHP script until the process is complete and then return when its complete.

Even if you set the ajax timeout to 0, your browser may not wait indefinitely: http://stackoverflow.com/questions/7297833/how-long-will-the-browser-wait-after-an-ajax-request — Mike Scotty, Jun 14 '16 at 14:08
The connection will time-out after some time, you should add the while/sleep in the front-end instead of the back-end. So do a request, get a false as result and after some seconds do an other request. — R Pelzer, Jun 14 '16 at 14:12
Ironically that was how I originally coded it, but I wasn't happy with the many PHP requests in the console window for debugging purposes, so I changed it, I didn't realise browsers can kill an active connection. — Single Entity, Jun 14 '16 at 14:16
What you are trying to do is similar to "long polling" in jQuery (similar problems may occur here). There are multiple articles about this out on the web — ssc-hrep3, Jun 14 '16 at 14:18
Ah indeed, I found this which is very informative: https://techoctave.com/c7/posts/60-simple-long-polling-example-with-javascript-and-jquery — Single Entity, Jun 14 '16 at 14:20
The above is what I was doing the first time round, well, I've learnt something here, thank you everybody. — Single Entity, Jun 14 '16 at 14:23

score 0 · Accepted Answer · answered Jun 16 '16 at 07:52

The problem is the browser was killing the PHP scripts connection, even though the script was configured not to time out for over an hour and was running as intended. I assume the browser thought it was not functioning correctly.

This implies polling a server using a long running PHP script isn't really possible, you have to do it on the JavaScript side or consider a more involved long polling solution which is explained nicely here:

https://techoctave.com/c7/posts/60-simple-long-polling-example-with-javascript-and-jquery

Big thanks to those in the comments of the question who answered this.

AJAX launched PHP script terminating without good reason

1 Answers1