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

Atomic updates and state


It is a common use case to read a data element, execute some logic, and update with a new value. For single-threaded programs, it bears no consequences, but for concurrent scenarios, the entire operation must be carried out in a lockstep as an atomic operation. This case is so common that many processors support this at the hardware level using a special Compare-and-swap (CAS) instruction, which is much cheaper than locking. On x86/x64 architectures, the instruction is called CompareExchange (CMPXCHG).

Unfortunately, it is possible that another thread updates the variable with the same value that the thread working on the atomic update is going to compare the old value against. This is known as the ABA problem. The set of instructions load-linked (LL) and store-conditional (SC), which are found in some other architectures, provide an alternative to CAS without the ABA problem. After the LL instruction reads the value from an address, the SC instruction to update...