Continue PHP execution after sending HTTP response

I had this snippet in my "special scripts" toolbox, but it got lost (clouds were not common back then), so I was searching for it and came up with this question, surprised to see that it's missing, I searched more and came back here to post it:

<?php ob_end_clean(); header("Connection: close"); ignore_user_abort(); // optional ob_start(); echo ('Text the user will see'); $size = ob_get_length(); header("Content-Length: $size"); ob_end_flush(); // Strange behaviour, will not work flush();            // Unless both are called ! session_write_close(); // Added a line suggested in the comment // Do processing here  sleep(30); echo('Text user will never see');?>

I actually use it in few places. And it totally makes sense there: a banklink is returning the request of a successful payment and I have to call a lot of services and process a lot of data when that happens. That sometimes takes more than 10 seconds, yet the banklink has fixed timeout period. So I acknowledge the banklink and show him the way out, and do my stuff when he is already gone.

Have the script that handles the initial request create an entry in a processing queue, and then immediately return. Then, create a separate process (via cron maybe) that regularly runs whatever jobs are pending in the queue.

What you need is this kind of setup