Chapter 1, Introduction to Reactive Programming, explains definitions of typical programming paradigms such as imperative, asynchronous, functional, parallel, and reactive programming. We’ll see what are the prerequisites to use functional programming in PHP and how all this is related to Reactive Extensions. At the end, we’ll introduce the RxPHP library as a tool of choice for this entire book.

Chapter 2, Reactive Programming with RxPHP, presents the basic concepts and common terminology used in reactive programming with RxPHP. It introduces Observables, observers, operators, Subjects, and disposables as the building blocks of any Rx application.

Chapter 3, Writing a Reddit Reader with RxPHP, builds on the knowledge from the previous chapter to write a Reddit reader application internally based on RxPHP. This will require downloading data via cURL and handling user input, and comparing the difference between blocking and non-blocking code in PHP in relation to RxPHP. We’ll also have a sneak peak into using event loops in PHP.

Chapter 4, Reactive versus a Typical Event-Driven Approach, shows that in order to use Rx in practice, we need to know how can we combine RxPHP code with some already existing code that isn’t based on Rx. For this reason, we’ll take the Event Dispatcher component that comes with the Symfony3 framework and extend it with Rx functionality.

Chapter 5, Testing RxPHP Code, covers testing, which is a crucial part of every development process. Apart from PHPUnit, we’ll also use the special testing classes that come with RxPHP out of the box. We’ll also take a look at testing asynchronous code in general and what caveats we need to be aware of.

Chapter 6, PHP Streams API and Higher-Order Observables, introduces the PHP Streams API and event loops. These two concepts are tightly coupled in RxPHP and we’ll learn why and how. We’ll talk about the issues we can encounter when using multiple event loops in the same application and how the PHP community is trying to solve them. We’ll also introduce the concept of higher-order Observables as a more advanced functionality of Rx.

Chapter 7, Implementing Socket IPC and WebSocket Server/Client, demonstrates how in order to write a more complicated asynchronous application, we’ll build a chat manager, server, and client as three separate processes that communicate with each other via Unix sockets and WebSockets. We’ll also use in practice the higher-order Observables from the previous chapter.

Chapter 8, Multicasting in RxPHP and PHP7 pthreads Extension, introduces us to the concept of multicasting in Rx and all the components that RxPHP provides for this purpose. We’ll also start using the pthreads extension for PHP7. This will let us run our code in parallel in multiple threads.

Chapter 9, Multithreaded and Distributed Computing with pthreads and Gearman, wraps the knowledge of pthreads from the previous chapter into reusable components that can be used together with RxPHP. We also introduce the Gearman framework as a way to distribute work among multiple processes. In the end, we’ll compare the pros and cons of using multiple threads and processes to run tasks in parallel.

Chapter 10, Using Advanced Operators and Techniques in RxPHP, will focus on not-so-common principles in Rx. These are mostly advanced operators for very specific tasks, but also implementation details of RxPHP components and their behavior in specific use cases that we should be aware of.

Appendix, Reusing RxPP Techniques in RxJS, demonstrates with practical examples how to deal with typical use cases where either RxPHP or RxJS come in handy. We'll see how asynchronous programming is used in a JavaScript environment and compare it to PHP. This final chapter also goes into more detail about what RxJS 5 is and how it differs from RxPHP.

The main prerequisites for most of this book are a PHP 5.6+ interpreter and any text editor.

We’ll use the Composer (https://getcomposer.org/) tool to install all external dependencies in our examples. Some basic knowledge of Composer and PHPUnit is helpful but not absolutely necessary.

In later chapters, we’ll also use the pthreads PHP extension, which requires PHP 7 or above and the Gearman job server; both should be available for all platforms.

Also, some basic knowledge of the Unix environment (sockets, processes, signals, and so on) is helpful.

This book is intended for intermediate developers with at least average knowledge of PHP who want to learn about asynchronous and reactive programming in PHP and Reactive Extensions in particular.

Apart from the RxPHP library, this book is framework agnostic, so you don’t need knowledge of any web framework.

All the topics regarding RxPHP are generally applicable to any Rx implementation, so switching from RxPHP to RxJS, for example, will be very easy.

In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "Every time we write an Observable, we'll extend the base Rx\Observable class."

A block of code is set as follows:

Rx\Observable::just('{"value":42}')
    ->lift(function() {
        return new JSONDecodeOperator();
    })
    ->subscribe(new DebugSubject());

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

use Rx\Observable\IntervalObservable;
class RedditCommand extends Command {
  /** @var \Rx\Subject\Subject */
  private $subject;
  private $interval;

Any command-line input or output is written as follows:

$ sleep.php proc1 3

proc1: 1

proc1: 2

proc1: 3

New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "PHP has to be compiled with the Thread Safety option enabled."

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