JSR 166 Snapshot Introduction.

by Doug Lea

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Disclaimer - This prototype is experimental code developed as part of JCP JSR166 and 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.

JSR166 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, prviding 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 thread pools. Descriptions of the main components may be found in the associated package documentation.

JSR166 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 java.util.Collection is introduced into java.util. Existing class java.util.LinkedList is adapted to support Queue, and a new non-thread-safe {@link java.util.PriorityQueue} is added.

Uncaught Exception Handlers

The java.lang.Thread class is modified to allow per-thread installation of handlers for uncaught exceptions. Ths optionally disassociates these handlers from ThreadGroups, which has proven to be too inflexible in many multithreaded programs. (Note that the combination of features in JSR166 make ThreadGroups even less likely to be used in most programs. Perhaps they will eventually be deprecated.)

High precision timing

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

Removing ThreadLocals

The 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