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revision 1.7 by dl, Tue Jul 8 00:46:24 2003 UTC revision 1.18 by dl, Sun Oct 17 11:45:00 2004 UTC
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1  <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">  <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
2  <html>  <html>
3   <head>   <head>
4     <title>JSR 166 Snapshot Introduction.</title>     <title>JSR 166 Introduction.</title>
5    </head>    </head>
6    
7    <body bgcolor="#ffffee" vlink="#0000aa" link="#cc0000">    <body bgcolor="#ffffee" vlink="#0000aa" link="#cc0000">
8    <h1>JSR 166 Snapshot Introduction.</h1>    <h1>JSR 166 Introduction.</h1>
9    
10    by <a href="http://gee.cs.oswego.edu/dl">Doug Lea</a>    by <a href="http://gee.cs.oswego.edu/dl">Doug Lea</a>
11    <p>    <p>
12    
13  To join a mailing list discussing this JSR, go to:  This is the updated JSR166 specification.  For further information, go
14  <A HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest"> http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A> .  to: <A
15    HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest">
16  <p>  http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A>.
17  <em>  
18   Disclaimer - This prototype is experimental code developed as part of  <p><em>Note: The javadocs here includes some existing java.util
19   JCP JSR166 and made available to the developer community for use  Collection interfaces and classes that are not part of the JSR-166
20   as-is. It is not a supported product. Use it at your own risk. The  spec, but are included because JSR-166 methods implement or inherit
21   specification, language and implementation are subject to change as a  from their specifications.</em>
22   result of your feedback. Because these features have not yet been  
23   approved for addition to the Java language, there is no schedule for  <p> JSR-166 introduces package <tt>java.util.concurrent</tt>
24   their inclusion in a product.  containing utility classes commonly useful in concurrent
25  </em>  programming. Like package <tt>java.util</tt>, it includes a few small
26    standardized extensible frameworks, as well as other classes that
27  <p> JSR166 introduces package <tt>java.util.concurrent</tt> containing utility  provide useful functionality and are otherwise tedious or difficult to
28  classes commonly useful in concurrent programming. Like package  implement.
29  java.util, it includes a few small standardized extensible frameworks,  
30  as well as some classes that provide useful functionality and are  <p>JSR-166 focusses on breadth, providing critical functionality
31  otherwise tedious or difficult to implement.  Descriptions of the main  useful across a wide range of concurrent programming styles and
32  components may be found in the associated package documentation.  applications, ranging from low-level atomic operations, to
33    customizable locks and synchronization aids, to various concurrent
34  <p> JSR166 also includes a few changes and additions in packages  data structures, to high-level execution agents including thread
35  outside of java.util.concurrent: java.lang, to address uncaught  pools. This diversity reflects the range of contexts in which
36  exceptions, and java.util to better integrate with collections.  Here  developers of concurrent programs have been found to require or desire
37  are brief descriptions.  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>  <h2>Queues</h2>
47    
48  A basic (nonblocking) {@link java.util.Queue} interface extending  A basic (nonblocking) {@link java.util.Queue} interface extending
49  java.util.Collection is introduced into java.util. Existing class  {@link java.util.Collection} is introduced into
50  java.util.LinkedList is adapted to support Queue, and a new  <tt>java.util</tt>. Existing class {@link java.util.LinkedList} is
51  non-thread-safe {@link java.util.PriorityQueue} is added.  adapted to support Queue, and a new non-thread-safe {@link
52    java.util.PriorityQueue} is added.
53  <h2>Uncaught Exception Handlers</h2>  
54    <h2>Threads</h2>
55  The java.lang.Thread class is modified to allow per-thread  
56  installation of handlers for uncaught exceptions. Ths optionally  Three minor changes are introduced to the {@link java.lang.Thread}
57  disassociates these handlers from ThreadGroups, which has proven to be  class:
58  too inflexible in many multithreaded programs. (Note that the  <ul>
59  combination of features in JSR166 make ThreadGroups even less likely    <li> It now allows per-thread installation of handlers for uncaught
60  to be used in most programs. Perhaps they will eventually be    exceptions. Ths optionally disassociates handlers from ThreadGroups,
61  deprecated.)    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  <p> Additionally, java.lang.ThreadLocal now supports a means to remove  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  a ThreadLocal, which is needed in some thread-pool and worker-thread
89  designs.  designs.
90    
91    
92    
93    <hr>    <hr>
   <address><A HREF="http://gee.cs.oswego.edu/dl">Doug Lea</A></address>  
94   </body>   </body>
95  </html>  </html>

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