JSR 166 Introduction.

by Doug Lea

This is an updated version of the specification submitted for JCP Public Review. To check for further updates, access a preliminary prototype release of main functionality, or join a mailing list discussing JSR-166, go to: http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest.

Note: The javadocs here includes some existing java.util Collection interfaces and classes that are not part of the JSR-166 spec, but are included because JSR-166 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 some 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 it makes sense 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.