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revision 1.8 by dl, Mon Jul 14 16:35:59 2003 UTC revision 1.12 by dl, Sat Aug 9 20:00:07 2003 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 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  there is no schedule for their inclusion in a product.  </em>
28  utility classes commonly useful in concurrent programming. Like  
29  package java.util, it includes a few small standardized extensible  <p> <em> <b>Disclaimer</b>.  This draft specification was produced
30  frameworks, as well as some classes that provide useful functionality  using JDK1.4 tools plus some preprocessing. The resulting javadocs do
31  and are otherwise tedious or difficult to implement. JSR-166 focusses  not yet correctly render other planned JDK1.5 constructs on which
32  on breadth, prviding critical functionality useful across a wide range  JSR-166 relies, most notably the use of generic types. We are
33  of concurrent programming styles and applications, ranging from  releasing this version now (before the availability of JDK1.5-based
34  low-level atomic operations, to customizable locks and synchronization  tools) because, even though they are misformatted and sometimes lack
35  aids, to various concurrent data structures, to thread pools.  proper cross-referencing, they otherwise convey the intended
36  Descriptions of the main components may be found in the associated  specifications.  </em>
37  package documentation.  
38    <p> JSR-166 introduces package <tt>java.util.concurrent</tt>
39  <p> JSR166 also includes a few changes and additions in packages  containing utility classes commonly useful in concurrent
40  outside of java.util.concurrent.  Here are brief descriptions.  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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