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.

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Table of Contents (19 chapters)
Learning Concurrent Programming in Scala - Second Edition
Learning Concurrent Programming in Scala - Second Edition
Credits
Credits
Foreword
Foreword
About the Author
About the Author
Acknowledgements
Acknowledgements
About the Reviewers
About the Reviewers
www.PacktPub.com
www.PacktPub.com
Customer Feedback
Customer Feedback
Preface
Preface
Free Chapter
1
Introduction
Introduction
Concurrent programming
The advantages of Scala
Preliminaries
Overview of new features in Scala 2.12
Summary
Exercises
2
Concurrency on the JVM and the Java Memory Model
Concurrency on the JVM and the Java Memory Model
Processes and threads
Monitors and synchronization
Volatile variables
The Java Memory Model
Summary
Exercises
3
Traditional Building Blocks of Concurrency
Traditional Building Blocks of Concurrency
The Executor and ExecutionContext objects
Atomic primitives
Lazy values
Concurrent collections
Custom concurrent data structures
Summary
Exercises
4
Asynchronous Programming with Futures and Promises
Asynchronous Programming with Futures and Promises
Futures
Promises
Futures and blocking
The Scala Async library
Alternative future frameworks
Summary
Exercises
5
Data-Parallel Collections
Data-Parallel Collections
Scala collections in a nutshell
Using parallel collections
Caveats with parallel collections
Using parallel and concurrent collections together
Implementing custom parallel collections
Summary
Exercises
6
Concurrent Programming with Reactive Extensions
Concurrent Programming with Reactive Extensions
Creating Observable objects
Composing Observable objects
Rx schedulers
Subjects and top-down reactive programming
Summary
Exercises
7
Software Transactional Memory
Software Transactional Memory
The trouble with atomic variables
Using Software Transactional Memory
Composing transactions
Retrying transactions
Transactional collections
Summary
Exercises
8
Actors
Actors
Working with actors
Communication between actors
Actor supervision
Remote actors
Summary
Exercises
9
Concurrency in Practice
Concurrency in Practice
Choosing the right tools for the job
Putting it all together - a remote file browser
Debugging concurrent programs
Summary
Exercises
10
Reactors
Reactors
The need for reactors
Getting started with Reactors
The "Hello World" program
Event streams
Reactors
Schedulers
Reactor lifecycle
Reactor system services
Protocols
Summary
Exercises

Exercises

In the following exercises, you are expected to define several reactor protocols. In some cases, the task is to first investigate a specific algorithm online on your own, and then implement it using the Reactors framework. The exercises are ordered by their difficulty, and range from simple tasks to more complex ones.

  1. Define a method called twice, which takes a target channel, and returns a channel that forwards every event twice to the target. 

            def twice[T](target: Channel[T]): Channel[T]

  2. Define a method called throttle, which throttles the rate at which events are forwarded to the target channel.

            def throttle[T](target: Channel[T]): Channel[T]

    Hint: you will have to use the Clock service and the functional event stream composition.

  3. The Shutdown service shown in this chapter can run out of memory if there are a lot of reactors subscribing to it. This is because the current implementation never removes entries from the service's subscribers map. Modify the custom...

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