JSR 166 Introduction.

by Doug Lea

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

Disclaimer. The prototype implementation is experimental code developed as part of JCP JSR-166 is made available to the developer community for use as-is. It is not a supported product. Use it at your own risk. The specification, language and implementation are subject to change as a result of your feedback. Because these features have not yet been approved for addition to the Java language, there is no schedule for their inclusion in a product.

Disclaimer. This draft specification was produced using JDK1.4 tools plus some preprocessing. The resulting javadocs do not yet correctly render other planned JDK1.5 constructs on which JSR-166 relies, most notably the use of generic types. We are releasing this version now (before the availability of JDK1.5-based tools) because, even though they are misformatted and sometimes lack proper cross-referencing, they otherwise convey the intended 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 that minimial support for which 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.
Doug Lea