Sometimes there are situations when you want to parallel process things. Other times you might have a list of tasks to accomplish, and you don't want to make the user wait after pressing a button. This is where "Workers" can come in. They are independent scripts that run along side of your application, performing tasks, or "jobs."
Solo is a very basic Perl script that ensures only one process of a type is running at once. Using this and a PHP library called predis, he shows how to set up workers and add items to your processing queue. The workers themselves run on a cron job and connect to the queue server to see what they need to do. He also throws in some "bells and whistles" - extras that can enhance your worker system: queue monitoring, version numbering and killing workers based on a hash value.