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

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