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

Actor supervision

When studying the actor lifecycle, we said that top-level user actors are by default restarted when an exception occurs. We now take a closer inspection at how this works. In Akka, every actor acts as a supervisor for its children. When a child fails, it suspends the processing messages, and sends a message to its parent to decide what to do about the failure. The policy that decides what happens to the parent and the child after the child fails is called the supervision strategy. The parent might decide to do the following:

  • Restart the actor, indicated with the Restart message

  • Resume the actor without a restart, indicated with the Resume message

  • Permanently stop the actor, indicated with the Stop message

  • Fail itself with the same exception, indicated with the Escalate message

By default, the user guardian actor comes with a supervision strategy that restarts the failed children actors. User actors stop their children by default. Both supervision strategies can be overridden...