Clojure is a remarkably high-performance language despite its dynamic nature. What really strikes you though is the fact that it combines performance with fundamental simplicity and pragmatism, which makes it such a joy to program in. Over the last six years since its first public release, Clojure has been heavily tested and deployed in production by many people and organizations across various domains. Its user base has grown rapidly during this period.
Clojure High Performance Programming is all about Clojure running on the Java Virtual Machine. The JVM has a reputation of being a robust platform to develop and deploy applications on. In this book, we take a deeper look at the performance characteristics of various features of Clojure and the underlying environment. We also explore what it takes to build well-performing software. We begin with the performance fundamentals and gradually proceed over to Clojure and other matters you may have to deal with while writing high-performance applications.
Understanding and achieving performance is both an art and a science, just like writing good software. Remember the big picture in the back of your mind but also be prepared to get into the details with measurement tools. More importantly, know how the software works and keenly study the environment in which it runs. I hope this book will help you on that path.
Chapter 1, Performance by Design, classifies the various use cases with respect to performance and analyzes how to interpret their performance aspects and needs.
Chapter 2, Clojure Abstractions, is a guided tour of various Clojure data structures, abstractions (persistent data structures, vars, macros, and so on), and their performance characteristics.
Chapter 3, Leaning on Java, discusses how to enhance performance by using Java interoperability and features from Clojure.
Chapter 4, Host Performance, discusses how the host stack impacts performance. Clojure being a hosted language, its performance is directly related to the host.
Chapter 5, Concurrency, is an advanced chapter that discusses concurrency and parallelism features in Clojure and the JVM. Concurrency is an increasingly significant way to derive performance.
Chapter 6, Optimizing Performance, discusses the systematic steps that need to be taken in order to obtain good performance.
Chapter 7, Application Performance, discusses building applications. This involves dealing with external subsystems and factors that impact the overall performance.
You should acquire Java Development Kit Version 7 or higher for your operating system to work through all examples. This book discusses the Oracle HotSpot JVM in specific situations, so you may want to get Oracle JDK or OpenJDK if possible. You should also get the latest Leiningen version (Version 2.3.3 as of the time of writing) from http://leiningen.org/ and JD-GUI from http://jd.benow.ca/.
This book is for intermediate Clojure programmers who are interested to learn how to write high-performance code. If you are an absolute beginner in Clojure, you should learn the basics of the language first and then come back later to this book. You need not be well-versed in performance engineering or Java. However, some prior knowledge of Java would make it much easier to understand the Java-related chapters.
In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.
Code words in text are shown as follows: "If you want Criterium to be available only in the REPL and not as a project dependency, add the following entry to the ~/.lein/profiles.clj file."
A block of code is set as follows:
(import 'java.util.concurrent.Callable) (import 'java.util.concurrent.Future) (def ^ExecutorService e (Executors/newSingleThreadExecutor)) (def ^Future f (.submit e (cast Callable #(reduce + (range 10000000))))) (.get f) ; blocks until result is processed, then returns it
New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "Clicking on the Next button moves you to the next screen."
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