asynchronous - Run PHP Task Asynchronously

Question

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 &");

Which appears to work, but I'm wondering if there's a better way. I'm considering writing a system which queues up tasks in a MySQL table, and a separate long-running PHP script that queries that table once a second, and executes any new tasks it finds. This would also have the advantage of letting me split the tasks among several worker machines in the future if I needed to.

Am I re-inventing the wheel? Is there a better solution than the exec() hack or the MySQL queue?

Answer 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:

• 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.