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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 JSR166 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><em>Note: The javadocs here do <em>not</em> include pre-existing
19 java classes (for example <code>java.lang.Thread</code>) that were changed
20 as part of the JSR166 spec. On the other hand, the javadocs here do
21 include some existing java.util Collection interfaces and classes that
22 are not part of the spec, but are included because some new methods
23 implement or inherit from their specifications.
24 </em>
26 <p>JSR-166 introduces package <code>java.util.concurrent</code>
27 containing utility classes commonly useful in concurrent
28 programming. Like package <code>java.util</code>, it includes a few small
29 standardized extensible frameworks, as well as other classes that
30 provide useful functionality and are otherwise tedious or difficult to
31 implement.
33 <p>JSR-166 focuses on breadth, providing critical functionality
34 useful across a wide range of concurrent programming styles and
35 applications, ranging from low-level atomic operations, to
36 customizable locks and synchronization aids, to various concurrent
37 data structures, to high-level execution agents including thread
38 pools. This diversity reflects the range of contexts in which
39 developers of concurrent programs have been found to require or desire
40 support not previously available in J2SE, which also keeping the
41 resulting package small; providing only functionality that has been
42 found to be worthwhile to standardize.
44 <p>Descriptions and brief motivations for the main components may be
45 found in the associated package documentation. JSR-166 also includes
46 a few changes and additions in packages outside of
47 java.util.concurrent. Here are brief descriptions.
49 <h2>Queues</h2>
51 A basic (nonblocking) {@link java.util.Queue} interface extending
52 {@link java.util.Collection} is introduced into
53 <code>java.util</code>. Existing class {@link java.util.LinkedList} is
54 adapted to support Queue, and a new non-thread-safe {@link
55 java.util.PriorityQueue} is added.
57 <h2>Threads</h2>
59 Three minor changes are introduced to the {@link java.lang.Thread}
60 class:
61 <ul>
62 <li> It now allows per-thread installation of handlers for uncaught
63 exceptions. This optionally disassociates handlers from ThreadGroups,
64 which has proven to be too inflexible. (Note that the combination of
65 features in JSR-166 make ThreadGroups even less likely to be used in
66 most programs. Perhaps they will eventually be deprecated.)
68 <li> Access checks are no longer required when a Thread interrupts
69 <em>itself</em>. The <code>interrupt</code> method is the only way to
70 re-assert a thread's interruption status (and in the case of
71 self-interruption has no other effect than this). The check here
72 previously caused unjustifiable and uncontrollable failures when
73 restricted code invoked library code that must reassert interruption
74 to correctly propagate status when encountering some
75 <code>InterruptedExceptions</code>.
76 <li> The <code>destroy</code> method, which has never been implemented,
77 has finally been deprecated. This is just a spec change, reflecting
78 the fact that that the reason it has never been implemented is that
79 it was undesirable and unworkable.
80 </ul>
82 <h2>Timing</h2>
84 Method <code>nanoTime</code> is added to {@link java.lang.System}. It
85 provides a high-precision timing facility that is distinct from and
86 uncoordinated with <code>System.currentTimeMillis</code>.
88 <h2>Removing ThreadLocals</h2>
90 The {@link java.lang.ThreadLocal} class now supports a means to remove
91 a ThreadLocal, which is needed in some thread-pool and worker-thread
92 designs.
96 <hr>
97 </body>
98 </html>

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