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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 an updated version of the specification submitted for JCP
14  <A HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest"> http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A> .  Community Draft review.  To check for further updates, access a
15    preliminary prototype release of main functionality, or join a mailing
16  <p>  list discussing this JSR, go to: <A
17  <em>  HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest">
18   Disclaimer - This prototype is experimental code developed as part of  http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A>
19   JCP JSR166 and made available to the developer community for use  .  <p>
20   as-is. It is not a supported product. Use it at your own risk. The  
21   specification, language and implementation are subject to change as a  <em> <b>Disclaimer</b>. The prototype implementation is experimental
22   result of your feedback. Because these features have not yet been  code developed as part of JCP JSR-166 is made available to the
23   approved for addition to the Java language, there is no schedule for  developer community for use as-is. It is not a supported product. Use
24   their inclusion in a product.  it at your own risk. The specification, language and implementation
25  </em>  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  <p> JSR166 introduces package <tt>java.util.concurrent</tt> containing utility  there is no schedule for their inclusion in a product.  </em>
28  classes commonly useful in concurrent programming. Like package  
29  java.util, it includes a few small standardized extensible frameworks,  <p> <em> <b>Disclaimer</b>.  This draft specification was produced
30  as well as some classes that provide useful functionality and are  using JDK1.4 tools plus some preprocessing. The resulting javadocs do
31  otherwise tedious or difficult to implement.  Descriptions of the main  not yet correctly render other planned JDK1.5 constructs on which
32  components may be found in the associated package documentation.  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  <p> JSR166 also includes a few changes and additions in packages  tools) because, even though they are misformatted and sometimes lack
35  outside of java.util.concurrent: java.lang, to address uncaught  proper cross-referencing, they otherwise convey the intended
36  exceptions, and java.util to better integrate with collections.  Here  specifications.  </em>
37  are brief descriptions.  
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.
44    
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.
55    
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    
61  <h2>Queues</h2>  <h2>Queues</h2>
62    
63  A basic (nonblocking) {@link java.util.Queue} interface extending  A basic (nonblocking) {@link java.util.Queue} interface extending
64  java.util.Collection is introduced into java.util. Existing class  {@link java.util.Collection} is introduced into
65  java.util.LinkedList is adapted to support Queue, and a new  <tt>java.util</tt>. Existing class {@link java.util.LinkedList} is
66  non-thread-safe {@link java.util.PriorityQueue} is added.  adapted to support Queue, and a new non-thread-safe {@link
67    java.util.PriorityQueue} is added.
68  <h2>Uncaught Exception Handlers</h2>  
69    <h2>Threads</h2>
70  The java.lang.Thread class is modified to allow per-thread  
71  installation of handlers for uncaught exceptions. Ths optionally  Three minor changes are introduced to the {@link java.lang.Thread}
72  disassociates these handlers from ThreadGroups, which has proven to be  class:
73  too inflexible in many multithreaded programs. (Note that the  <ul>
74  combination of features in JSR166 make ThreadGroups even less likely    <li> It now allows per-thread installation of handlers for uncaught
75  to be used in most programs. Perhaps they will eventually be    exceptions. Ths optionally disassociates handlers from ThreadGroups,
76  deprecated.)    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.)
79    
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    
94    <h2>Timing</h2>
95    
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    
100    <h2>Removing ThreadLocals</h2>
101    
102  <p> Additionally, java.lang.ThreadLocal now supports a means to remove  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  a ThreadLocal, which is needed in some thread-pool and worker-thread
104  designs.  designs.
105    
106    
107    
108    <hr>    <hr>
109    <address><A HREF="http://gee.cs.oswego.edu/dl">Doug Lea</A></address>    <address><A HREF="http://gee.cs.oswego.edu/dl">Doug Lea</A></address>
110   </body>   </body>

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