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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN"> |
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<title>JSR 166 Introduction.</title> |
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<body bgcolor="#ffffee" vlink="#0000aa" link="#cc0000"> |
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<h1>JSR 166 Introduction.</h1> |
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by <a href="http://gee.cs.oswego.edu/dl">Doug Lea</a> |
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<p> |
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This is maintenance repository of JSR166 specifications. For further |
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information, go to: <A |
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HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest"> |
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http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A>. |
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<p><em>Note: The javadocs here do <em>not</em> include pre-existing |
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java classes (for example <tt>java.lang.Thread</tt>) that were changed |
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as part of the JSR166 spec. On the other hand, the javadocs here so |
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include some existing java.util Collection interfaces and classes that |
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are not part of the spec, but are included because some new methods |
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implement or inherit from their specifications. |
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</em> |
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<p> JSR-166 introduces package <tt>java.util.concurrent</tt> |
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containing utility classes commonly useful in concurrent |
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programming. Like package <tt>java.util</tt>, it includes a few small |
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standardized extensible frameworks, as well as other classes that |
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provide useful functionality and are otherwise tedious or difficult to |
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implement. |
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<p>JSR-166 focusses on breadth, providing critical functionality |
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useful across a wide range of concurrent programming styles and |
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applications, ranging from low-level atomic operations, to |
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customizable locks and synchronization aids, to various concurrent |
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data structures, to high-level execution agents including thread |
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pools. This diversity reflects the range of contexts in which |
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developers of concurrent programs have been found to require or desire |
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support not previously available in J2SE, which also keeping the |
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resulting package small; providing only functionality that has been |
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found to be worthwhile to standardize. |
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<p>Descriptions and brief motivations for the main components may be |
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found in the associated package documentation. JSR-166 also includes |
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a few changes and additions in packages outside of |
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java.util.concurrent. Here are brief descriptions. |
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<h2>Queues</h2> |
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A basic (nonblocking) {@link java.util.Queue} interface extending |
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{@link java.util.Collection} is introduced into |
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<tt>java.util</tt>. Existing class {@link java.util.LinkedList} is |
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adapted to support Queue, and a new non-thread-safe {@link |
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java.util.PriorityQueue} is added. |
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<h2>Threads</h2> |
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Three minor changes are introduced to the {@link java.lang.Thread} |
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class: |
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<ul> |
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<li> It now allows per-thread installation of handlers for uncaught |
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exceptions. Ths optionally disassociates handlers from ThreadGroups, |
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which has proven to be too inflexible. (Note that the combination of |
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features in JSR-166 make ThreadGroups even less likely to be used in |
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most programs. Perhaps they will eventually be deprecated.) |
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<li> Access checks are no longer required when a Thread interrupts |
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<em>itself</em>. The <tt>interrupt</tt> method is the only way to |
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re-assert a thread's interruption status (and in the case of |
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self-interruption has no other effect than this). The check here |
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previously caused unjustifiable and uncontrollable failures when |
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restricted code invoked library code that must reassert interruption |
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to correctly propagate status when encountering some |
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<tt>InterruptedExceptions</tt>. |
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<li> The <tt>destroy</tt> method, which has never been implemented, |
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has finally been deprecated. This is just a spec change, reflecting |
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the fact that that the reason it has never been implemented is that |
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it was undesirable and unworkable. |
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</ul> |
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<h2>Timing</h2> |
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Method <tt>nanoTime</tt> is added to {@link java.lang.System}. It |
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provides a high-precision timing facility that is distinct from and |
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uncoordinated with <tt>System.currentTimeMillis</tt>. |
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<h2>Removing ThreadLocals</h2> |
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The {@link java.lang.ThreadLocal} class now supports a means to remove |
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a ThreadLocal, which is needed in some thread-pool and worker-thread |
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designs. |
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<hr> |
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</body> |
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</html> |
