PHP Cookbook

Chapter 17. Asynchronous PHP

Many basic PHP scripts handle operations synchronously—meaning the script runs one monolithic process from start to finish and only does one thing at a time. However, more sophisticated applications have become commonplace in the world of PHP, so more advanced modes of operation are required as well. Namely, asynchronous programming has quickly become a rising concept for PHP developers. Learning how to do two (or more) things at the same time within your scripts is vital to building modern applications.

Two words come up frequently when discussing asynchronous programming: concurrent and parallel. When most people talk about parallel programming, what they really mean to say is concurrent programming. With concurrency, your application does two things but not necessarily at the same time. Think of a single barista serving multiple customers at once—the barista is multitasking and making several different drinks but can really only make one drink at a time.

With parallel operations, you are doing two different things simultaneously. Imagine installing a drip coffee machine on the counter in the cafe. Some patrons are still being served by the barista, but others can get their caffeine fix from a separate machine in parallel. Figure 17-1 depicts concurrent and parallel operations through the barista analogy.

Figure 17-1. Concurrent versus parallel modes ...