Not Waiting for Response from an AJAX Request

You might want to check out the answers to This Question. Basically when you make your ajax call to a php function which calls the exec() function as shown in the answers to that question, you'll get an ajax response almost immediately, since your php function doesn't actually need to process anything. This way, it shouldn't matter if the user leaves the page. Here's a small example:

ajax call in html file: $.ajax({url: 'blah.php'});

blah.php file: exec('bash -c "exec nohup setsid php really_slow_script.php > /dev/null 2>&1 &"');

And then finally in really_slow_script.php, just include the actual code you want to run.

I successfully used this kind of logic to allow users to post an already uploaded video from their account on my website to youtube. (The video had to be sent to youtube, and since videos are generally large files, I didn't want the user to have to wait while the video was being uploaded to youtube)