Book Image

Concurrent Patterns and Best Practices

By : Atul S. Khot
Book Image

Concurrent Patterns and Best Practices

By: Atul S. Khot

Overview of this book

Selecting the correct concurrency architecture has a significant impact on the design and performance of your applications. Concurrent design patterns help you understand the different characteristics of parallel architecture to make your code faster and more efficient. This book will help Java developers take a hands-on approach to building scalable and distributed apps by following step-by-step explanations of essential concepts and practical examples. You’ll begin with basic concurrency concepts and delve into the patterns used for explicit locking, lock-free programming, futures, and actors. You’ll explore coding with multithreading design patterns, including master, slave, leader, follower, and map-reduce, and then move on to solve problems using synchronizer patterns. You'll even discover the rationale for these patterns in distributed and parallel applications, and understand how future composition, immutability, and the monadic flow help you create more robust code. By the end of the book, you’ll be able to use concurrent design patterns to build high performance applications confidently.
Table of Contents (14 chapters)


Thank you for purchasing this book! We live in a concurrent world and concurrent programming is an increasingly valuable skill.

I still remember the Aha! moment when I understood how UNIX shell pipeline works. I fell headlong in love with Linux and the command line and tried out many combination filters (a filter is a program reading from standard input and writes to standard output) connected via pipes. I was amazed by the creativity and power brought about by the command line. I was working with concurrent programs.

Then, there was a change of project and I was thrown headlong into writing code using the multithreaded paradigm. The language was C or C++, which I loved deeply; however, to my surprise I found that it was a herculean effort to maintain a legacy code base, written in C/C++ that was multithreaded. The shared state was managed in a haphazard way and a small mistake could throw us into a debugging nightmare!

Around that time, I came to know about object oriented (OO) design patterns and some multithreaded patterns as well. For example, we wanted to expose a big in-memory data structure safely to many threads. I had read about the Readers/Writer lock pattern, which used smart pointers (a C++ idiom) and coded a solution based on it.

Voila! It just worked. The concurrency bugs simply disappeared! Furthermore, the pattern made it very easy to reason about threads. In our case, a writer thread needed infrequent but exclusive access to the shared data structure. The reader threads just used the structure as an immutable entity—and look mom, no locks!

No locks! Well, well, well... this was something new! As the locks disappeared, so did any possibility of deadlocks, races, and starvation! It felt just great!

There was a lesson I learned here! Keep learning about design patterns and try to think about the design problem at hand - in terms of patterns. This also helped me reason better about the code! Finally, I had an inkling of how to tame the concurrency beast! 

Design patterns are reusable design solutions for common design problems. The design solutions are design patterns. Your problem domain may vary, that is, the business logic you need to write will be applicable to solving the business problem at hand. However, once you apply the pattern, things just fall in place, more or less!

For example, when we code using the OO paradigm, we use the Gang Of Four (GOF) design patterns ( This famous book provides us a catalog of design problems and their solutions. The strategy pattern is used by people in various contexts—the pattern though remains the same.

Some years later, I moved to the Java world and used the executor service to structure my code. It was very easy to develop the code and it worked without any major problem for months (There were other issues, but no data races and no nightmarish debugging!).

Subsequently, I moved to the functional world and started writing more and more Scala. This was a new world  with immutable data structures as the norm. I learned about a very different paradigm; Scala's Futures and Akka Actors gave a whole different perspective. I could feel the power these tools give you as a programmer. Once you pass the learning curve (admittedly a little daunting at the beginning), you are equipped to write a lot safer concurrent code which is also a lot easier to reason about.   

The book you are reading talks of many concurrent design patterns. It shows the rationale behind these patterns and highlights the design theme. 

Who this book is for

You should  have done some Java programming and ideally have played with multithreaded Java programs.  Ideally you should have some familiarity with the gang of four (GoF) design patterns. You should also be comfortable running Java programs via maven.  

This book will take you to the next level while showing you the design theme behind many concurrency patterns. This book hopes to help developers who want to learn patterns to build scalable and high performing apps.

What this book covers

Chapter 1, Concurrency - An Introduction, provides an introduction to concurrent programming. As you will see, concurrency is a world in itself. You will look at Unix processes and the pipes and filters for concurrency pattern. The chapter covers an overview of concurrent programming. You probably know some of this material already.

Chapter 2, A Taste of Some Concurrency Patterns, covers some essential basic concepts. The essence of the Java Memory Model is introduced. You will also look at race conditions and problems arising out of the shared state model. You will get a taste of the first concurrency pattern—hand-over-hand locking.

Chapter 3, More Threading Patterns, covers explicitly synchronizing the mutable state and the monitor pattern. You will see how this approach is fraught with problems. We wrap up with a detailed look at the Active Object design pattern.

Chapter 4, Thread Pools, covers how threads communicate via the producer/consumer pattern. The concept of thread communication is introduced. Then, the Master/Slave design pattern is explained. The chapter wraps up with another look at the map-reduce pattern as a special case of the fork-join pattern.

Chapter 5, Increasing the Concurrency, talks about the building blocks. Things such as blocking queues, bounded queues, latches, FutureTask, semaphores, and barrier are discussed. We talk about being live and safety. Finally, we describe immutability and how immutable data structures are inherently thread safe.

Chapter 6, Functional Concurrency Patterns, introduces futures and talks about its monadic nature. We cover the transformation and monad patterns and illustrate how futures compose. We also look at promises.

Chapter 7, Actors Patterns, introduces the Actor paradigm. We recall the Active Object again and then explain the actor paradigm—especially the no explicit locks nature of things. We discuss patterns such as ask versus tell, the become pattern (and stressing immutability), pipelining, and half sync or half async. We discuss these patterns and illustrate them via example code.

To get the most out of this book

To get the most out of this book, you should have a decent level of Java programming knowledge. It is assumed that you know the basics of Java threading. Here I cover the essential aspects as a refresher. Having worked through some Java threading examples would be definite plus. You should also be comfortable using maven, the Java build tool.

Using an IDE of your choice IntelliJ Idea, Eclipse or Netbeans would be helpful - but is not strictly necessary.  To illustrate the functional concurrency patterns - the last two chapters use Scala. The code uses basic Scala constructs. It would be good to go through an introductory Scala tutorial - and you should be good to go. 

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Conventions used

There are a number of text conventions used throughout this book.

CodeInText: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: "Mount the downloaded WebStorm-10*.dmg disk image file as another disk in your system."

A block of code is set as follows:

html, body, #map {
 height: 100%; 
 margin: 0;
 padding: 0

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

exten => s,1,Dial(Zap/1|30)
exten => s,2,Voicemail(u100)
exten => s,102,Voicemail(b100)
exten => i,1,Voicemail(s0)

Any command-line input or output is written as follows:

$ mkdir css
$ cd css

Bold: Indicates a new term, an important word, or words that you see onscreen. For example, words in menus or dialog boxes appear in the text like this. Here is an example: "Select System info from the Administration panel."


Warnings or important notes appear like this.


Tips and tricks appear like this.

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