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
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Using parallel and concurrent collections together

We have already seen that parallel collection operations are not allowed to access mutable states without the use of synchronization. This includes modifying sequential Scala collections from within a parallel operation. Recall that we used a mutable variable in the section on side effects to count the size of the intersection. In the following example, we will download the URL and HTML specifications, convert them to sets of words, and try to find an intersection of their words. In the intersection method, we use a HashSet collection and update it in parallel. Collections in the scala.collection.mutable package are not thread-safe. The following example nondeterministically drops elements, corrupts the buffer state, or throws exceptions:

object ConcurrentWrong extends App { 
  import ParHtmlSearch.getHtmlSpec 
  import ch4.FuturesCallbacks.getUrlSpec 
  def intersection(a: GenSet[String], b: GenSet[String]) = {