Book Image

Clojure High Performance Programming

By : Shantanu Kumar
Book Image

Clojure High Performance Programming

By: Shantanu Kumar

Overview of this book

<p>Clojure is a young, dynamic, functional programming language that runs on the Java Virtual Machine. It is built with performance, pragmatism, and simplicity in mind. Like most general purpose languages, Clojure’s features have different performance characteristics that one should know in order to write high performance code.<br /><br />Clojure High Performance Programming is a practical, to-the-point guide that shows you how to evaluate the performance implications of different Clojure abstractions, learn about their underpinnings, and apply the right approach for optimum performance in real-world programs.<br /><br />This book discusses the Clojure language in the light of performance factors that you can exploit in your own code.</p> <p>You will also learn about hardware and JVM internals that also impact Clojure’s performance. Key features include performance vocabulary, performance analysis, optimization techniques, and how to apply these to your programs. You will also find detailed information on Clojure's concurrency, state-management, and parallelization primitives.</p> <p>This book is your key to writing high performance Clojure code using the right abstraction, in the right place, using the right technique.</p>
Table of Contents (15 chapters)
Clojure High Performance Programming
Credits
About the Author
Acknowledgments
About the Reviewers
www.PacktPub.com
Preface
Index

Transients


Earlier in this chapter, we discussed the virtues of immutability and the pitfalls of mutability. However, even though unguarded mutability is fundamentally unsafe, it also has very good single-threaded performance. Now, what if there was a way to restrict the mutable operation in a local context in order to provide safety guarantees? That would be equivalent to combining the performance advantage and local safety guarantees. This can be done with the abstraction called transients, which is provided by Clojure.

First, let us verify that it is safe:

user=> (let [t (transient [:a])]
  @(future (conj! t :b)))
IllegalAccessError Transient used by non-owner thread  clojure.lang.PersistentVector$TransientVector.ensureEditable (PersistentVector.java:463)

As we can see, a transient created in one thread cannot be accessed by another:

user=> (let [t (transient [:a])] (seq t))

IllegalArgumentException Don't know how to create ISeq from: clojure.lang.PersistentVector$TransientVector ...