Book Image

Learning Concurrent Programming in Scala - Second Edition

By : Aleksandar Prokopec
Book Image

Learning Concurrent Programming in Scala - Second Edition

By: Aleksandar Prokopec

Overview of this book

Scala is a modern, multiparadigm programming language designed to express common programming patterns in a concise, elegant, and type-safe way. Scala smoothly integrates the features of object-oriented and functional languages. In this second edition, you will find updated coverage of the Scala 2.12 platform. The Scala 2.12 series targets Java 8 and requires it for execution. The book starts by introducing you to the foundations of concurrent programming on the JVM, outlining the basics of the Java Memory Model, and then shows some of the classic building blocks of concurrency, such as the atomic variables, thread pools, and concurrent data structures, along with the caveats of traditional concurrency. The book then walks you through different high-level concurrency abstractions, each tailored toward a specific class of programming tasks, while touching on the latest advancements of async programming capabilities of Scala. It also covers some useful patterns and idioms to use with the techniques described. Finally, the book presents an overview of when to use which concurrency library and demonstrates how they all work together, and then presents new exciting approaches to building concurrent and distributed systems. Who this book is written for If you are a Scala programmer with no prior knowledge of concurrent programming, or seeking to broaden your existing knowledge about concurrency, this book is for you. Basic knowledge of the Scala programming language will be helpful.
Table of Contents (19 chapters)
Learning Concurrent Programming in Scala - Second Edition
About the Author
About the Reviewers
Customer Feedback

Event streams

In this section, we study the basic data-type that drives most computations in the Reactors framework: an event stream. Event streams represent special program values that can occasionally produce events. Event streams are represented by the Event[T] type.

Semantically, an event stream is very similar to the Observable type, which we saw in Chapter 6, Concurrent Programming with Reactive Extensions. As we will see, the main difference between Observable and Events is that an Observable object can generally be used from different threads, and even emit events across different threads when the observeOn method is used. An Events object, by contrast, can only be used inside the reactor that owns that event stream.


Never share an event stream between two reactors. An event stream can only be used by the reactor that owns the corresponding channel.

In the following, we show an example event stream called myEvents, which produces events of type String:

val myEvents: Events[String...