JSR 166 Introduction.

by Doug Lea

This is maintenance repository of JSR166 specifications. For further information, go to: http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest.

Note: The javadocs here do not include pre-existing java classes (for example java.lang.Thread) that were changed as part of the JSR166 spec. On the other hand, the javadocs here do include some existing java.util Collection interfaces and classes that are not part of the spec, but are included because some new methods implement or inherit from their specifications.

JSR-166 introduces package java.util.concurrent containing utility classes commonly useful in concurrent programming. Like package java.util, it includes a few small standardized extensible frameworks, as well as other classes that provide useful functionality and are otherwise tedious or difficult to implement.

JSR-166 focusses on breadth, providing critical functionality useful across a wide range of concurrent programming styles and applications, ranging from low-level atomic operations, to customizable locks and synchronization aids, to various concurrent data structures, to high-level execution agents including thread pools. This diversity reflects the range of contexts in which developers of concurrent programs have been found to require or desire support not previously available in J2SE, which also keeping the resulting package small; providing only functionality that has been found to be worthwhile to standardize.

Descriptions and brief motivations for the main components may be found in the associated package documentation. JSR-166 also includes a few changes and additions in packages outside of java.util.concurrent. Here are brief descriptions.


A basic (nonblocking) {@link java.util.Queue} interface extending {@link java.util.Collection} is introduced into java.util. Existing class {@link java.util.LinkedList} is adapted to support Queue, and a new non-thread-safe {@link java.util.PriorityQueue} is added.


Three minor changes are introduced to the {@link java.lang.Thread} class:


Method nanoTime is added to {@link java.lang.System}. It provides a high-precision timing facility that is distinct from and uncoordinated with System.currentTimeMillis.

Removing ThreadLocals

The {@link java.lang.ThreadLocal} class now supports a means to remove a ThreadLocal, which is needed in some thread-pool and worker-thread designs.