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The Java Memory Model is a part of the Java Language Specification that covers, among other topics, the effects of synchronization by means of locks, the use of volatile and atomic variable, the guarantees given for final fields. It has been around since the advent of Java and underwent a major overhaul in release 5.0 of Java. Despite of its existence since day one of Java it is an area of the language that many developers do not feel comfortable with.  It is considered guru knowledge and best ignored. Avoidance, however, is no longer practical.

These days the prevalence of multicore processors requires that essentially all Java applications must be multi-threaded if the want to take advantage of the available cpu power. Inevitably many applications will make the transition from a single-core architecture to a multi-core or multi-cpu platform.  This migration occasionally reveals (so far dormant) bugs in the program: applications that worked properly and reliably in a single-core context suddenly and inexplicably exhibit errors in a multi-core context. Often this is due to the substantially more aggressive caching techniques used on the processor level in combination with misconceptions regarding the Java Memory Model on the programmer's side.  In order to avoid such misconeptions, the workshop discusses the Java Memory Model comprehensively and in depth.

A proper understanding of the Java Memory Model does not only help tracking down and fixing bugs.  In addition, it allows development Java programs with perceivably higher performance.

The elimination or at least reduction of sychronization is becoming increasingly  important in a multi-core and multi-processor world.  Using a multi-cpu platform users expect that an application should scale, that is, its performance should increase with the number of available cpus.  This highly desirable effect does not occur automatically, but has to be built into the application.  Sequential, i.e., non-parallel, parts of the program must be drastically reduced in order to utilize the multiple cpus effectively.  There are several technique for reduction of sequential processing, among them the elimination of lock-based sychronization, but also the use of atomic operations and programming techniques such as lock-free programming.

The workshop discusses the Java Memory Model, the issues of visibilty and reordering, the use of volatile and atomic variable, the implementation of immutable types based on the memory model's initialization safety garantee, and provides an introduction to the techniques of lock-free programming.

In this workshop, participants have the opportunity to practice and apply the newly gained knowledge in hands-on labs.  They will review code, spot bugs, and fix them.  In addition, they will use atomic variables to eleminate lock-based synchronisation.  
 

This is a course for Java programmers who want to round up their knowledge of Java concurrency issues.

The course is designed to build on existing expertise as Java programmers and aims to take the skills one step further. Prerequisite for the seminar is sound knowledge of Java concurrency and substantial  practical experience with concurrent programming in Java. 

OBJECTIVES

	Know when to replace locks by volatile and atomics
	Understand the effects of locks, volatile, final and atomics
	Learn how to avoid subtle visibility bugs
	Understand the principles of  lock-free programming

The course is designed by Klaus Kreft & Angelika Langer and backed by years of experience in teaching  Java related topics and more than a decade of real-world experience in industrial software development in Java.

Angelika Langer is a freelance trainer/mentor in the area of object-oriented software development in C++ and Java. She is a recognized author and speaker at conferences worldwide and author of the Java Generics FAQ .

Klaus Kreft is a senior consultant for more than 20 years and has served as the lead architect on several successful industry projects. He develops in Java since 1995. He is a regular speaker at OO conferences in Germany.

Together they are authors of the book "Standard C++ IOStreams and Locales" and numerous articles on C++ and Java topics in various computer magazines worldwide, including the column "Effective Java" in the German JavaMagazin. 

• Purpose of the Java memory model
• Visibility, atomicity, reordering
• Garantees for volatile 
• Double-checked locking
• Initialisation safety of final fields
• Atomic variables
• Lock-free programming