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2  <html>  <html>
3   <head>   <head>
4     <title>JSR 166 Snapshot Introduction.</title>     <title>JSR 166 Introduction.</title>
5    </head>    </head>
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>
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>
13  To join a mailing list discussing this JSR, go to:  This is an updated version of the specification submitted for JCP Public
14  <A HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest"> http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A> .  Review.  To check for further updates, access a preliminary prototype
15    release of main functionality, or join a mailing list discussing
16  <p>  JSR-166, 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  
20   as-is. It is not a supported product. Use it at your own risk. The  <p><em>Note: The javadocs here includes some existing java.util
21   specification, language and implementation are subject to change as a  Collection interfaces and classes that are not part of the JSR-166
22   result of your feedback. Because these features have not yet been  spec, but are included because JSR-166 methods implement or inherit
23   approved for addition to the Java language, there is no schedule for  from their specifications.</em>
24   their inclusion in a product.  
25  </em>  <p> JSR-166 introduces package <tt>java.util.concurrent</tt>
26    containing utility classes commonly useful in concurrent
27  <p> JSR166 introduces package <tt>java.util.concurrent</tt> containing utility  programming. Like package <tt>java.util</tt>, it includes a few small
28  classes commonly useful in concurrent programming. Like package  standardized extensible frameworks, as well as some classes that
29  java.util, it includes a few small standardized extensible frameworks,  provide useful functionality and are otherwise tedious or difficult to
30  as well as some classes that provide useful functionality and are  implement.
31  otherwise tedious or difficult to implement.  Descriptions of the main  
32  components may be found in the associated package documentation.  <p>JSR-166 focusses on breadth, providing critical functionality
33    useful across a wide range of concurrent programming styles and
34  <p> JSR166 also includes a few changes and additions in packages  applications, ranging from low-level atomic operations, to
35  outside of java.util.concurrent: java.lang, to address uncaught  customizable locks and synchronization aids, to various concurrent
36  exceptions, and java.util to better integrate with collections.  Here  data structures, to high-level execution agents including thread
37  are brief descriptions.  pools. This diversity reflects the range of contexts in which
38    developers of concurrent programs have been found to require or desire
39    support not previously available in J2SE, which also keeping the
40    resulting package small; providing only functionality that it makes
41    sense to standardize.
43    <p>Descriptions and brief motivations for the main components may be
44    found in the associated package documentation.  JSR-166 also includes
45    a few changes and additions in packages outside of
46    java.util.concurrent.  Here are brief descriptions.
48  <h2>Queues</h2>  <h2>Queues</h2>
50  A basic (nonblocking) {@link java.util.Queue} interface extending  A basic (nonblocking) {@link java.util.Queue} interface extending
51  java.util.Collection is introduced into java.util. Existing class  {@link java.util.Collection} is introduced into
52  java.util.LinkedList is adapted to support Queue, and a new  <tt>java.util</tt>. Existing class {@link java.util.LinkedList} is
53  non-thread-safe {@link java.util.PriorityQueue} is added.  adapted to support Queue, and a new non-thread-safe {@link
54    java.util.PriorityQueue} is added.
55  <h2>Uncaught Exception Handlers</h2>  
56    <h2>Threads</h2>
57  The java.lang.Thread class is modified to allow per-thread  
58  installation of handlers for uncaught exceptions. Ths optionally  Three minor changes are introduced to the {@link java.lang.Thread}
59  disassociates these handlers from ThreadGroups, which has proven to be  class:
60  too inflexible in many multithreaded programs. (Note that the  <ul>
61  combination of features in JSR166 make ThreadGroups even less likely    <li> It now allows per-thread installation of handlers for uncaught
62  to be used in most programs. Perhaps they will eventually be    exceptions. Ths optionally disassociates handlers from ThreadGroups,
63  deprecated.)    which has proven to be too inflexible. (Note that the combination of
64      features in JSR-166 make ThreadGroups even less likely to be used in
65      most programs. Perhaps they will eventually be deprecated.)
67      <li> Access checks are no longer required when a Thread interrupts
68      <em>itself</em>.  The <tt>interrupt</tt> method is the only way to
69      re-assert a thread's interruption status (and in the case of
70      self-interruption has no other effect than this).  The check here
71      previously caused unjustifiable and uncontrollable failures when
72      restricted code invoked library code that must reassert interruption
73      to correctly propagate status when encountering some
74      <tt>InterruptedExceptions</tt>.
75      <li> The <tt>destroy</tt> method, which has never been implemented,
76      has finally been deprecated. This is just a spec change, reflecting
77      the fact that that the reason it has never been implmented is that
78      it was undesirable and unworkable.
79    </ul>
81    <h2>Timing</h2>
83    Method <tt>nanoTime</tt> is added to {@link java.lang.System}. It
84    provides a high-precision timing facility that is distinct from and
85    uncoordinated with <tt>System.currentTimeMillis</tt>.
87    <h2>Removing ThreadLocals</h2>
89  <p> Additionally, java.lang.ThreadLocal now supports a means to remove  The {@link java.lang.ThreadLocal} class now supports a means to remove
90  a ThreadLocal, which is needed in some thread-pool and worker-thread  a ThreadLocal, which is needed in some thread-pool and worker-thread
91  designs.  designs.
95    <hr>    <hr>
   <address><A HREF="http://gee.cs.oswego.edu/dl">Doug Lea</A></address>  
96   </body>   </body>
97  </html>  </html>

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