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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 JSR166 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><em>Note: The javadocs here do <em>not</em> include pre-existing
19   JCP JSR166 and made available to the developer community for use  java classes (for example <tt>java.lang.Thread</tt>) that were changed
20   as-is. It is not a supported product. Use it at your own risk. The  as part of the JSR166 spec.  On the other hand, the javadocs here so
21   specification, language and implementation are subject to change as a  include some existing java.util Collection interfaces and classes that
22   result of your feedback. Because these features have not yet been  are not part of the spec, but are included because some new methods
23   approved for addition to the Java language, there is no schedule for  implement or inherit from their specifications.
  their inclusion in a product.  
24  </em>  </em>
25    
26  <p> JSR166 introduces package <tt>java.util.concurrent</tt> containing utility  <p> JSR-166 introduces package <tt>java.util.concurrent</tt>
27  classes commonly useful in concurrent programming. Like package  containing utility classes commonly useful in concurrent
28  java.util, it includes a few small standardized extensible frameworks,  programming. Like package <tt>java.util</tt>, it includes a few small
29  as well as some classes that provide useful functionality and are  standardized extensible frameworks, as well as other classes that
30  otherwise tedious or difficult to implement.  Descriptions of the main  provide useful functionality and are otherwise tedious or difficult to
31  components may be found in the associated package documentation.  implement.
32    
33  <p> JSR166 also includes a few changes and additions in packages  <p>JSR-166 focusses on breadth, providing critical functionality
34  outside of java.util.concurrent: java.lang, to address uncaught  useful across a wide range of concurrent programming styles and
35  exceptions, and java.util to better integrate with collections.  Here  applications, ranging from low-level atomic operations, to
36  are brief descriptions.  customizable locks and synchronization aids, to various concurrent
37    data structures, to high-level execution agents including thread
38    pools. This diversity reflects the range of contexts in which
39    developers of concurrent programs have been found to require or desire
40    support not previously available in J2SE, which also keeping the
41    resulting package small; providing only functionality that has been
42    found to be worthwhile to standardize.
43    
44    <p>Descriptions and brief motivations for the main components may be
45    found in the associated package documentation.  JSR-166 also includes
46    a few changes and additions in packages outside of
47    java.util.concurrent.  Here are brief descriptions.
48    
49  <h2>Queues</h2>  <h2>Queues</h2>
50    
51  A basic (nonblocking) {@link java.util.Queue} interface extending  A basic (nonblocking) {@link java.util.Queue} interface extending
52  java.util.Collection is introduced into java.util. Existing class  {@link java.util.Collection} is introduced into
53  java.util.LinkedList is adapted to support Queue, and a new  <tt>java.util</tt>. Existing class {@link java.util.LinkedList} is
54  non-thread-safe {@link java.util.PriorityQueue} is added.  adapted to support Queue, and a new non-thread-safe {@link
55    java.util.PriorityQueue} is added.
56  <h2>Uncaught Exception Handlers</h2>  
57    <h2>Threads</h2>
58  The java.lang.Thread class is modified to allow per-thread  
59  installation of handlers for uncaught exceptions. Ths optionally  Three minor changes are introduced to the {@link java.lang.Thread}
60  disassociates these handlers from ThreadGroups, which has proven to be  class:
61  too inflexible in many multithreaded programs. (Note that the  <ul>
62  combination of features in JSR166 make ThreadGroups even less likely    <li> It now allows per-thread installation of handlers for uncaught
63  to be used in most programs. Perhaps they will eventually be    exceptions. Ths optionally disassociates handlers from ThreadGroups,
64  deprecated.)    which has proven to be too inflexible. (Note that the combination of
65      features in JSR-166 make ThreadGroups even less likely to be used in
66      most programs. Perhaps they will eventually be deprecated.)
67    
68      <li> Access checks are no longer required when a Thread interrupts
69      <em>itself</em>.  The <tt>interrupt</tt> method is the only way to
70      re-assert a thread's interruption status (and in the case of
71      self-interruption has no other effect than this).  The check here
72      previously caused unjustifiable and uncontrollable failures when
73      restricted code invoked library code that must reassert interruption
74      to correctly propagate status when encountering some
75      <tt>InterruptedExceptions</tt>.
76      <li> The <tt>destroy</tt> method, which has never been implemented,
77      has finally been deprecated. This is just a spec change, reflecting
78      the fact that that the reason it has never been implemented is that
79      it was undesirable and unworkable.
80    </ul>
81    
82    <h2>Timing</h2>
83    
84    Method <tt>nanoTime</tt> is added to {@link java.lang.System}. It
85    provides a high-precision timing facility that is distinct from and
86    uncoordinated with <tt>System.currentTimeMillis</tt>.
87    
88    <h2>Removing ThreadLocals</h2>
89    
90  <p> Additionally, java.lang.ThreadLocal now supports a means to remove  The {@link java.lang.ThreadLocal} class now supports a means to remove
91  a ThreadLocal, which is needed in some thread-pool and worker-thread  a ThreadLocal, which is needed in some thread-pool and worker-thread
92  designs.  designs.
93    
94    
95    
96    <hr>    <hr>
   <address><A HREF="http://gee.cs.oswego.edu/dl">Doug Lea</A></address>  
97   </body>   </body>
98  </html>  </html>
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