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

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