The Java Memory Model: The Building Block of Concurrency
TS-1630

This session describes the Java Memory Model (JSR 133) and how it affects the ways concurrent software should be written. The Java technology memory model was revised by JSR 133, and the revision was incorporated into Java Platform, Enterprise Edition 5. This change redefined the semantics of threads, synchronization, volatile variables, and final fields. This redefinition is compatible with existing good programming practice, although care needs to be taken in regard to a couple of corner cases. More important, the new memory model provides new efficient techniques for safely and correctly implementing concurrent operations.

Many programmers can avoid depending on low-level details and instead just use high-level concurrency abstractions provided in the new concurrency libraries. However, for those who have to write their own concurrency abstractions, understanding the building blocks of concurrency can be vitally important.

The presentation provides a simple and clear definition of what synchronization actually does, discusses the semantics of volatile variables and the java.util.concurrent.atomic package and how they can be used to create efficient concurrent implementations, and describes how final fields can be used to provide thread-safe immutable objects without synchronization.

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