In a post to the Madewithlove blog Maxime Fabre takes a look at threading in PHP using the pthreads support that can be included into your PHP installation.

As far as I can remember, PHP has always had a terrible reputation at handling very heavy (or asynchronous) tasks. [...] But PHP can do threading, and more importantly it's a lot easier than you probably think.

[...] In this article I'm going to dive into the pthreads extension (short for POSIX Threads). It has been around for a while (since 2012) but I feel like too many people forget it exists or assume it is going to be painful to use – mostly because the official documentation is rather slim about it.

They start by getting the pthreads support installed locally (it assumes you use OS X and the "brew" package manager but it can be installed manually too). The article starts off by defining some basic nomenclature from the pthreads world and gives a diagram of how it all fits together. From there it gets into some examples, showing a simple thread class to fetch Google results and how to fire off multiple instances at the same time. They then extend this even further and look at the concept of "workers" and using them to manage individual jobs. It then moves up the next level and looks at "pools" of workers and processing multiple workers at the same time.

There's also a section dealing with one "gotcha" that can happen with class inheritance between parent and child threads. They show how to work around this with a custom Worker class that performs the autoloading for you and is executed at the start of a Pool. Finally they cover the messaging between the child threads and, as a bonus, how threading could be used in a command bus setup.