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2     <html>
3     <head>
4 dl 1.12 <title>JSR 166 Introduction.</title>
5 tim 1.1 </head>
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>
13 dl 1.12 This is an updated version of the specification submitted for JCP
14     Community Draft review. To check for further updates, access a
15     preliminary prototype release of main functionality, or join a mailing
16     list discussing this JSR, go to: <A
17 dl 1.9 HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest">
18     http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A>
19 dl 1.12 . <p>
20 dl 1.7
21 dl 1.9 <em> <b>Disclaimer</b>. The prototype implementation is experimental
22     code developed as part of JCP JSR-166 is made available to the
23     developer community for use as-is. It is not a supported product. Use
24     it at your own risk. The specification, language and implementation
25     are subject to change as a result of your feedback. Because these
26     features have not yet been approved for addition to the Java language,
27     there is no schedule for their inclusion in a product. </em>
29     <p> <em> <b>Disclaimer</b>. This draft specification was produced
30     using JDK1.4 tools plus some preprocessing. The resulting javadocs do
31     not yet correctly render other planned JDK1.5 constructs on which
32     JSR-166 relies, most notably the use of generic types. We are
33     releasing this version now (before the availability of JDK1.5-based
34     tools) because, even though they are misformatted and sometimes lack
35     proper cross-referencing, they otherwise convey the intended
36     specifications. </em>
38     <p> JSR-166 introduces package <tt>java.util.concurrent</tt>
39     containing utility classes commonly useful in concurrent
40     programming. Like package <tt>java.util</tt>, it includes a few small
41     standardized extensible frameworks, as well as some classes that
42     provide useful functionality and are otherwise tedious or difficult to
43     implement.
45     <p>JSR-166 focusses on breadth, providing critical functionality
46     useful across a wide range of concurrent programming styles and
47     applications, ranging from low-level atomic operations, to
48     customizable locks and synchronization aids, to various concurrent
49     data structures, to high-level execution agents including thread
50     pools. This diversity reflects the range of contexts in which
51     developers of concurrent programs have been found to require or desire
52     support not previously available in J2SE, which also keeping the
53     resulting package small; providing only that minimial support for
54     which it makes sense to standardize.
56     <p>Descriptions and brief motivations for the main components may be
57     found in the associated package documentation. JSR-166 also includes
58     a few changes and additions in packages outside of
59     java.util.concurrent. Here are brief descriptions.
60 tim 1.1
61     <h2>Queues</h2>
63 dl 1.3 A basic (nonblocking) {@link java.util.Queue} interface extending
64 dl 1.9 {@link java.util.Collection} is introduced into
65     <tt>java.util</tt>. Existing class {@link java.util.LinkedList} is
66     adapted to support Queue, and a new non-thread-safe {@link
67     java.util.PriorityQueue} is added.
69     <h2>Threads</h2>
71 dl 1.13 Three minor changes are introduced to the {@link java.lang.Thread}
72     class:
73     <ul>
74     <li> It now allows per-thread installation of handlers for uncaught
75     exceptions. Ths optionally disassociates handlers from ThreadGroups,
76     which has proven to be too inflexible. (Note that the combination of
77     features in JSR-166 make ThreadGroups even less likely to be used in
78     most programs. Perhaps they will eventually be deprecated.)
80     <li> Access checks are no longer required when a Thread interrupts
81     <em>itself</em>. The <tt>interrupt</tt> method is the only way to
82     re-assert a thread's interruption status (and in the case of
83     self-interruption has no other effect than this). The check here
84     previously caused unjustifiable and uncontrollable failures when
85     restricted code invoked library code that must reassert interruption
86     to correctly propagate status when encountering some
87     <tt>InterruptedExceptions</tt>.
88     <li> The <tt>destroy</tt> method, which has never been implemented,
89     has finally been deprecated. This is just a spec change, reflecting
90     the fact that that the reason it has never been implmented is that
91     it was undesirable and unworkable.
92     </ul>
93 dl 1.9
94     <h2>Timing</h2>
96     Method <tt>nanoTime</tt> is added to {@link java.lang.System}. It
97     provides a high-precision timing facility that is distinct from and
98     uncoordinated with <tt>System.currentTimeMillis</tt>.
99 dl 1.8
100     <h2>Removing ThreadLocals</h2>
102 dl 1.9 The {@link java.lang.ThreadLocal} class now supports a means to remove
103     a ThreadLocal, which is needed in some thread-pool and worker-thread
104 dl 1.2 designs.
105 dl 1.9
107 tim 1.1
108     <hr>
109     <address><A HREF="http://gee.cs.oswego.edu/dl">Doug Lea</A></address>
110     </body>
111     </html>

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