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1 <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
2 <html>
3 <head>
4 <title>JSR 166 Introduction.</title>
5 </head>
6
7 <body bgcolor="#ffffee" vlink="#0000aa" link="#cc0000">
8 <h1>JSR 166 Introduction.</h1>
9
10 by <a href="http://gee.cs.oswego.edu/dl">Doug Lea</a>
11 <p>
12
13 This is the proposed final draft JSR166 specification. To check for
14 further updates, or join a mailing list discussing JSR-166, 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>.
17
18 <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
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 standardized extensible frameworks, as well as other classes that
27 provide useful functionality and are otherwise tedious or difficult to
28 implement.
29
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 resulting package small; providing only functionality that has been
39 found to be worthwhile to standardize.
40
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
46 <h2>Queues</h2>
47
48 A basic (nonblocking) {@link java.util.Queue} interface extending
49 {@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.
53
54 <h2>Threads</h2>
55
56 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.)
64
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 the fact that that the reason it has never been implemented is that
76 it was undesirable and unworkable.
77 </ul>
78
79 <h2>Timing</h2>
80
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
85 <h2>Removing ThreadLocals</h2>
86
87 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 designs.
90
91
92
93 <hr>
94 </body>
95 </html>

dl@cs.oswego.edu
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