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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 Community Review Draft 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>JJSR 166 Community Review Draft 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:  To chack for updates to this draft, access a preliminary prototype
14  <A HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest"> http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A> .  release of main functionality, or join a mailing list discussing this
15    JSR, go to: <A
16    HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest">
17    http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A>
18    .
19  <p>  <p>
 <em>  
  Disclaimer - This prototype is experimental code developed as part of  
  JCP JSR166 and made available to the developer community for use  
  as-is. It is not a supported product. Use it at your own risk. The  
  specification, language and implementation are subject to change as a  
  result of your feedback. Because these features have not yet been  
  approved for addition to the Java language, there is no schedule for  
  their inclusion in a product.  
 </em>  
   
 <p> JSR166 introduces package <tt>java.util.concurrent</tt> containing  
 utility classes commonly useful in concurrent programming. Like  
 package java.util, it includes a few small standardized extensible  
 frameworks, as well as some classes that provide useful functionality  
 and are otherwise tedious or difficult to implement. JSR-166 focusses  
 on breadth, prviding critical functionality useful across a wide range  
 of concurrent programming styles and applications, ranging from  
 low-level atomic operations, to customizable locks and synchronization  
 aids, to various concurrent data structures, to thread pools.  
 Descriptions of the main components may be found in the associated  
 package documentation.  
20    
21  <p> JSR166 also includes a few changes and additions in packages  <em> <b>Disclaimer</b>. The prototype implementation is experimental
22  outside of java.util.concurrent.  Here are brief descriptions.  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>
28    
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>
37    
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  Two minor changes are introduced to the {@link java.lang.Thread}
72  disassociates these handlers from ThreadGroups, which has proven to be  class: It now allows per-thread installation of handlers for uncaught
73  too inflexible in many multithreaded programs. (Note that the  exceptions. Ths optionally disassociates handlers from ThreadGroups,
74  combination of features in JSR166 make ThreadGroups even less likely  which has proven to be too inflexible. (Note that the combination of
75  to be used in most programs. Perhaps they will eventually be  features in JSR-166 make ThreadGroups even less likely to be used in
76  deprecated.)  most programs. Perhaps they will eventually be deprecated.) Secondly,
77    access checks are no longer required when a Thread interrupts
78  <h2>High precision timing</h2>  <em>itself</em>.  The <tt>interrupt</tt> method is the only way to
79    re-assert a thread's interruption status (and in the case of
80  Method <tt>nanoTime</tt> is added to <tt>java.lang.System</tt>. It  self-interruption has no other effect than this).  The check here
81  provides a high-precision timing facility that is distinct from  previously caused unjustifiable and uncontrollable failures when
82  and uncoordinated with <tt>System.currentTimeMillis</tt>.  restricted code invoked library code that must reassert interruption
83    to correctly propagate status when encountering some
84    <tt>InterruptedExceptions</tt>.
85    
86    <h2>Timing</h2>
87    
88    Method <tt>nanoTime</tt> is added to {@link java.lang.System}. It
89    provides a high-precision timing facility that is distinct from and
90    uncoordinated with <tt>System.currentTimeMillis</tt>.
91    
92  <h2>Removing ThreadLocals</h2>  <h2>Removing ThreadLocals</h2>
93    
94  The java.lang.ThreadLocal class now supports a means to remove a  The {@link java.lang.ThreadLocal} class now supports a means to remove
95  ThreadLocal, which is needed in some thread-pool and worker-thread  a ThreadLocal, which is needed in some thread-pool and worker-thread
96  designs.  designs.
97    
98    
99    
100    <hr>    <hr>
101    <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>
102   </body>   </body>

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