Coroutines on the other hand have received relatively little attention. The reason is that coroutines are both a lot more powerful and a lot harder to understand and explain. In this article I'd like to guide you through an implementation of a task scheduler using coroutines, so you can get a feeling for the stuff that they allow you to do. I'll start off with a few introductory sections. If you feel like you already got a good grasp of the basics behind generators and coroutines, then you can jump straight to the "Cooperative multitasking" section.

He starts with a look at generators, a piece of functionality that will allow PHP to, for example, more easily create iterators "on the fly." He then moves on to coroutines, added functions that you have two-way communication with generators instead of just pulling data from them. With the basics out of the way, he gets into the "cooperative multitasking" and a sample socket-based server he implements using some of the concepts.