The SitePoint PHP blog has another tutorial posted from author Christopher Pitt looking at writing async libraries with PHP. In this particular article he focuses on just one of many tasks an asynchronous library could perform: converting HTML to PDF documents.

I can barely remember a conference where the topic of asynchronous PHP wasn’t discussed. I am pleased that it’s so frequently spoken about these days. There’s a secret these speakers aren’t telling, though: "Making asynchronous servers, resolving domain names, interacting with file systems: these are the easy things. Making your own asynchronous libraries is hard. And it’s where you spend most of your time!"

The reason those easy things are easy is because they were the proof of concept – to make async PHP competitive with NodeJS. [...] Today, we’re going to look at a few ways to make your application code work well in an asynchronous architecture. Fret not – your code can still work in a synchronous architecture, so you don’t have to give anything up to learn this new skill. Apart from a bit of time…

He starts with some theory about things in the async world including callbacks, promises and what they might look like in PHP-land. He then starts in on the creation of the PDF files, creating a "Driver" class to handle some of the logic and using the Dompdf library to do the heavy lifting (the conversion from HTML to PDF). He walks through the code required for this class then moves on to the code, using the Amp project, to handle the async operations. He then creates a simple set of web accessible endpoints that call the Driver class with some basic attributes and performing the conversion. He ends the post talking about porting the parallel driver to other systems (such as ReactPHP) and a few simple steps if you need to move back to the synchronous world.