JSR 166 Introduction.

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.

Queues

Threads

• It now allows per-thread installation of handlers for uncaught exceptions. Ths optionally disassociates handlers from ThreadGroups, which has proven to be too inflexible. (Note that the combination of features in JSR-166 make ThreadGroups even less likely to be used in most programs. Perhaps they will eventually be deprecated.)
• Access checks are no longer required when a Thread interrupts itself. The interrupt method is the only way to re-assert a thread's interruption status (and in the case of self-interruption has no other effect than this). The check here previously caused unjustifiable and uncontrollable failures when restricted code invoked library code that must reassert interruption to correctly propagate status when encountering some InterruptedExceptions.
• The destroy method, which has never been implemented, has finally been deprecated. This is just a spec change, reflecting the fact that that the reason it has never been implmented is that it was undesirable and unworkable.

Timing

Removing ThreadLocals