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1 tim 1.1 <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
2     <html>
3     <head>
4 dl 1.12 <title>JSR 166 Introduction.</title>
5 tim 1.1 </head>
6    
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>
12    
13 jsr166 1.25 This is maintenance repository of JSR-166 specifications. For further
14 dl 1.19 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 jsr166 1.24 <p>JSR-166 introduces package <code>java.util.concurrent</code>
19 dl 1.9 containing utility classes commonly useful in concurrent
20 jsr166 1.24 programming. Like package <code>java.util</code>, it includes a few small
21 dl 1.16 standardized extensible frameworks, as well as other classes that
22 dl 1.9 provide useful functionality and are otherwise tedious or difficult to
23     implement.
24    
25 jsr166 1.22 <p>JSR-166 focuses on breadth, providing critical functionality
26 dl 1.9 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 jsr166 1.25 support not previously available in J2SE, while also keeping the
33 dl 1.16 resulting package small; providing only functionality that has been
34     found to be worthwhile to standardize.
35 dl 1.9
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.
40 tim 1.1
41     <h2>Queues</h2>
42    
43 dl 1.3 A basic (nonblocking) {@link java.util.Queue} interface extending
44 dl 1.9 {@link java.util.Collection} is introduced into
45 jsr166 1.24 <code>java.util</code>. Existing class {@link java.util.LinkedList} is
46 dl 1.9 adapted to support Queue, and a new non-thread-safe {@link
47     java.util.PriorityQueue} is added.
48    
49     <h2>Threads</h2>
50    
51 dl 1.13 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 jsr166 1.22 exceptions. This optionally disassociates handlers from ThreadGroups,
56 dl 1.13 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.)
59    
60     <li> Access checks are no longer required when a Thread interrupts
61 jsr166 1.24 <em>itself</em>. The <code>interrupt</code> method is the only way to
62 dl 1.13 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 jsr166 1.24 <code>InterruptedExceptions</code>.
68     <li> The <code>destroy</code> method, which has never been implemented,
69 dl 1.13 has finally been deprecated. This is just a spec change, reflecting
70 dl 1.23 the fact that the reason it has never been implemented is that
71 dl 1.13 it was undesirable and unworkable.
72     </ul>
73 dl 1.9
74     <h2>Timing</h2>
75    
76 jsr166 1.24 Method <code>nanoTime</code> is added to {@link java.lang.System}. It
77 dl 1.9 provides a high-precision timing facility that is distinct from and
78 jsr166 1.24 uncoordinated with <code>System.currentTimeMillis</code>.
79 dl 1.8
80     <h2>Removing ThreadLocals</h2>
81    
82 dl 1.9 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 dl 1.2 designs.
85 dl 1.9
86    
87 tim 1.1
88     <hr>
89     </body>
90     </html>

dl@cs.oswego.edu
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