I work on a somewhat large web application, and the backend is mostly in PHP. There are several places in the code where I need to complete some task, but I don't want to make the user wait for the result. For example, when creating a new account, I need to send them a welcome email. But when they hit the 'Finish Registration' button, I don't want to make them wait until the email is actually sent, I just want to start the process, and return a message to the user right away.
Up until now, in some places I've been using what feels like a hack with exec(). Basically doing things like:
exec("doTask.php $arg1 $arg2 $arg3 >/dev/null 2>&1 &");
I've used the queuing approach, and it works well as you can defer that processing until your server load is idle, letting you manage your load quite effectively if you can partition off "tasks which aren't urgent" easily.
Rolling your own isn't too tricky, here's a few other options to check out:
Another, perhaps simpler, approach is to use ignore_user_abort - once you've sent the page to the user, you can do your final processing without fear of premature termination, though this does have the effect of appearing to prolong the page load from the user perspective.