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2     <html>
3     <head>
4 dl 1.12 <title>JSR 166 Introduction.</title>
5 tim 1.1 </head>
7     <body bgcolor="#ffffee" vlink="#0000aa" link="#cc0000">
8 dl 1.12 <h1>JSR 166 Introduction.</h1>
9 tim 1.1
10     by <a href="http://gee.cs.oswego.edu/dl">Doug Lea</a>
11     <p>
13 dl 1.17 This is the final JSR166 specification submitted to JCP. For further
14     information, go to: <A
15 dl 1.9 HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest">
16 dl 1.14 http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A>.
17 dl 1.7
18 dl 1.14 <p><em>Note: The javadocs here includes some existing java.util
19     Collection interfaces and classes that are not part of the JSR-166
20     spec, but are included because JSR-166 methods implement or inherit
21     from their specifications.</em>
22 dl 1.9
23     <p> JSR-166 introduces package <tt>java.util.concurrent</tt>
24     containing utility classes commonly useful in concurrent
25     programming. Like package <tt>java.util</tt>, it includes a few small
26 dl 1.16 standardized extensible frameworks, as well as other classes that
27 dl 1.9 provide useful functionality and are otherwise tedious or difficult to
28     implement.
30     <p>JSR-166 focusses on breadth, providing critical functionality
31     useful across a wide range of concurrent programming styles and
32     applications, ranging from low-level atomic operations, to
33     customizable locks and synchronization aids, to various concurrent
34     data structures, to high-level execution agents including thread
35     pools. This diversity reflects the range of contexts in which
36     developers of concurrent programs have been found to require or desire
37     support not previously available in J2SE, which also keeping the
38 dl 1.16 resulting package small; providing only functionality that has been
39     found to be worthwhile to standardize.
40 dl 1.9
41     <p>Descriptions and brief motivations for the main components may be
42     found in the associated package documentation. JSR-166 also includes
43     a few changes and additions in packages outside of
44     java.util.concurrent. Here are brief descriptions.
45 tim 1.1
46     <h2>Queues</h2>
48 dl 1.3 A basic (nonblocking) {@link java.util.Queue} interface extending
49 dl 1.9 {@link java.util.Collection} is introduced into
50     <tt>java.util</tt>. Existing class {@link java.util.LinkedList} is
51     adapted to support Queue, and a new non-thread-safe {@link
52     java.util.PriorityQueue} is added.
54     <h2>Threads</h2>
56 dl 1.13 Three minor changes are introduced to the {@link java.lang.Thread}
57     class:
58     <ul>
59     <li> It now allows per-thread installation of handlers for uncaught
60     exceptions. Ths optionally disassociates handlers from ThreadGroups,
61     which has proven to be too inflexible. (Note that the combination of
62     features in JSR-166 make ThreadGroups even less likely to be used in
63     most programs. Perhaps they will eventually be deprecated.)
65     <li> Access checks are no longer required when a Thread interrupts
66     <em>itself</em>. The <tt>interrupt</tt> method is the only way to
67     re-assert a thread's interruption status (and in the case of
68     self-interruption has no other effect than this). The check here
69     previously caused unjustifiable and uncontrollable failures when
70     restricted code invoked library code that must reassert interruption
71     to correctly propagate status when encountering some
72     <tt>InterruptedExceptions</tt>.
73     <li> The <tt>destroy</tt> method, which has never been implemented,
74     has finally been deprecated. This is just a spec change, reflecting
75 dl 1.15 the fact that that the reason it has never been implemented is that
76 dl 1.13 it was undesirable and unworkable.
77     </ul>
78 dl 1.9
79     <h2>Timing</h2>
81     Method <tt>nanoTime</tt> is added to {@link java.lang.System}. It
82     provides a high-precision timing facility that is distinct from and
83     uncoordinated with <tt>System.currentTimeMillis</tt>.
84 dl 1.8
85     <h2>Removing ThreadLocals</h2>
87 dl 1.9 The {@link java.lang.ThreadLocal} class now supports a means to remove
88     a ThreadLocal, which is needed in some thread-pool and worker-thread
89 dl 1.2 designs.
90 dl 1.9
92 tim 1.1
93     <hr>
94     </body>
95     </html>

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