Run PHP Task Asynchronously

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:

• GearMan - this answer was written in 2009, and since then GearMan looks a popular option, see comments below.
• ActiveMQ if you want a full blown open source message queue.
• ZeroMQ - this is a pretty cool socket library which makes it easy to write distributed code without having to worry too much about the socket programming itself. You could use it for message queuing on a single host - you would simply have your webapp push something to a queue that a continuously running console app would consume at the next suitable opportunity
• beanstalkd - only found this one while writing this answer, but looks interesting
• dropr is a PHP based message queue project, but hasn't been actively maintained since Sep 2010
• php-enqueue is a recently (2017) maintained wrapper around a variety of queue systems
• Finally, a blog post about using memcached for message queuing

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.

When you just want to execute one or several HTTP requests without having to wait for the response, there is a simple PHP solution, as well.

In the calling script:

$socketcon = fsockopen($host, 80, $errno, $errstr, 10);
if($socketcon) {   
   $socketdata = "GET $remote_house/script.php?parameters=... HTTP 1.1\r\nHost: $host\r\nConnection: Close\r\n\r\n";      
   fwrite($socketcon, $socketdata); 
   fclose($socketcon);
}
// repeat this with different parameters as often as you like

On the called script.php, you can invoke these PHP functions in the first lines:

ignore_user_abort(true);
set_time_limit(0);

This causes the script to continue running without time limit when the HTTP connection is closed.