How this book is organized
The primary goal of this book is to help you develop skills that are necessary to write correct and efficient concurrent programs. The best way to obtain a skill is to apply it in practice. When it comes to programming, the best way to learn it is to write programs. This book aims to teach you about concurrency in Scala through a sequence of example programs, each designed to show you a particular aspect of concurrent programming. The examples range from the simplest counterparts of a "Hello World" program to programs demonstrating advanced intricacies of concurrency.
What is common to most of the programs in this book is that they are short and self-contained. This has two benefits. First, you can study most of the examples in isolation. Although we recommend that you read the entire book in the order of the chapters, you should have no problem studying specific topics. Second, conciseness ensures that each new concept is easy to grasp and understand. It is much easier to comprehend concepts like atomicity, memory contention, or busy-waiting on simple programs. This does not mean that these programs are contrived or artificial; each example illustrates an effect present in real-world programs, although stripped of irrelevant nonessentials.
When reading this book, we strongly encourage you to write down and run these examples yourself, rather than just passively study them. Each example will teach you about a new concept, but you can only fully understand each of these concepts if you try them in practice. Witnessing a particular effect in a running concurrent program is a far more valuable experience than just reading about it. So, make sure that you download SBT, and create an empty project before starting to read this book, as described later in a subsequent section. The examples are made short so that you, the reader, can try them out with almost no hassle.
At the end of each chapter, you will find a list of programming exercises. These exercises are designed to test your understanding of the various topics that have been introduced. We recommend that you try to solve at least a few after completing a chapter.
In most cases, we avoid listing the API methods, or their exact signatures. There are several reasons for this. First, you can always study the APIs in the online ScalaDoc documentation. This book would not be particularly useful if it simply repeated the content that's already there. Second, software is in a constant state of change. Although the Scala concurrency framework designers strive to keep the APIs stable, the method names and signatures are occasionally changed. This book describes the semantics of the most important concurrency facilities that are sufficient to write concurrent programs and unlikely to change.
The goal of this book is not to give a comprehensive overview of every dark corner of the Scala concurrency APIs. Instead, this book will teach you the most important concepts of concurrent programming. By the time you are done reading this book, you will not just be able to find additional information in the online documentation; you will also know what to look for. Rather than serving as a complete API reference and feeding you the exact semantics of every method, the purpose of this book is to teach you how to fish. By the time you are done reading, you will not only understand how different concurrency libraries work, but you will also know how to think when building a concurrent program.
