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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 maintenance repository of JSR-166 specifications.  For further
14  <A HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest"> http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A> .  information, go 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>JSR-166 introduces package <code>java.util.concurrent</code>
19   JCP JSR166 and made available to the developer community for use  containing utility classes commonly useful in concurrent
20   as-is. It is not a supported product. Use it at your own risk. The  programming. Like package <code>java.util</code>, it includes a few small
21   specification, language and implementation are subject to change as a  standardized extensible frameworks, as well as other classes that
22   result of your feedback. Because these features have not yet been  provide useful functionality and are otherwise tedious or difficult to
23   approved for addition to the Java language, there is no schedule for  implement.
24   their inclusion in a product.  
25  </em>  <p>JSR-166 focuses on breadth, providing critical functionality
26    useful across a wide range of concurrent programming styles and
27  <p> JSR166 introduces package <tt>java.util.concurrent</tt> containing  applications, ranging from low-level atomic operations, to
28  utility classes commonly useful in concurrent programming. Like  customizable locks and synchronization aids, to various concurrent
29  package java.util, it includes a few small standardized extensible  data structures, to high-level execution agents including thread
30  frameworks, as well as some classes that provide useful functionality  pools. This diversity reflects the range of contexts in which
31  and are otherwise tedious or difficult to implement. JSR-166 focusses  developers of concurrent programs have been found to require or desire
32  on breadth, prviding critical functionality useful across a wide range  support not previously available in J2SE, while also keeping the
33  of concurrent programming styles and applications, ranging from  resulting package small; providing only functionality that has been
34  low-level atomic operations, to customizable locks and synchronization  found to be worthwhile to standardize.
35  aids, to various concurrent data structures, to thread pools.  
36  Descriptions of the main components may be found in the associated  <p>Descriptions and brief motivations for the main components may be
37  package documentation.  found in the associated package documentation.  JSR-166 also includes
38    a few changes and additions in packages outside of
39  <p> JSR166 also includes a few changes and additions in packages  java.util.concurrent.  Here are brief descriptions.
 outside of java.util.concurrent.  Here are brief descriptions.  
40    
41  <h2>Queues</h2>  <h2>Queues</h2>
42    
43  A basic (nonblocking) {@link java.util.Queue} interface extending  A basic (nonblocking) {@link java.util.Queue} interface extending
44  java.util.Collection is introduced into java.util. Existing class  {@link java.util.Collection} is introduced into
45  java.util.LinkedList is adapted to support Queue, and a new  <code>java.util</code>. Existing class {@link java.util.LinkedList} is
46  non-thread-safe {@link java.util.PriorityQueue} is added.  adapted to support Queue, and a new non-thread-safe {@link
47    java.util.PriorityQueue} is added.
48  <h2>Uncaught Exception Handlers</h2>  
49    <h2>Threads</h2>
50  The java.lang.Thread class is modified to allow per-thread  
51  installation of handlers for uncaught exceptions. Ths optionally  Three minor changes are introduced to the {@link java.lang.Thread}
52  disassociates these handlers from ThreadGroups, which has proven to be  class:
53  too inflexible in many multithreaded programs. (Note that the  <ul>
54  combination of features in JSR166 make ThreadGroups even less likely    <li> It now allows per-thread installation of handlers for uncaught
55  to be used in most programs. Perhaps they will eventually be    exceptions. This optionally disassociates handlers from ThreadGroups,
56  deprecated.)    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  <h2>High precision timing</h2>    most programs. Perhaps they will eventually be deprecated.)
59    
60  Method <tt>nanoTime</tt> is added to <tt>java.lang.System</tt>. It    <li> Access checks are no longer required when a Thread interrupts
61  provides a high-precision timing facility that is distinct from    <em>itself</em>.  The <code>interrupt</code> method is the only way to
62  and uncoordinated with <tt>System.currentTimeMillis</tt>.    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      <code>InterruptedExceptions</code>.
68      <li> The <code>destroy</code> method, which has never been implemented,
69      has finally been deprecated. This is just a spec change, reflecting
70      the fact that the reason it has never been implemented is that
71      it was undesirable and unworkable.
72    </ul>
73    
74    <h2>Timing</h2>
75    
76    Method <code>nanoTime</code> is added to {@link java.lang.System}. It
77    provides a high-precision timing facility that is distinct from and
78    uncoordinated with <code>System.currentTimeMillis</code>.
79    
80  <h2>Removing ThreadLocals</h2>  <h2>Removing ThreadLocals</h2>
81    
82  The java.lang.ThreadLocal class now supports a means to remove a  The {@link java.lang.ThreadLocal} class now supports a means to remove
83  ThreadLocal, which is needed in some thread-pool and worker-thread  a ThreadLocal, which is needed in some thread-pool and worker-thread
84  designs.  designs.
85    
86    
87    
88    <hr>    <hr>
   <address><A HREF="http://gee.cs.oswego.edu/dl">Doug Lea</A></address>  
89   </body>   </body>
90  </html>  </html>

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