1 |
|
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN"> |
2 |
|
<html> |
3 |
|
<head> |
4 |
< |
<title>JSR 166 Snapshot Introduction.</title> |
4 |
> |
<title>JSR 166 Introduction.</title> |
5 |
|
</head> |
6 |
|
|
7 |
|
<body bgcolor="#ffffee" vlink="#0000aa" link="#cc0000"> |
8 |
< |
<h1>JSR 166 Snapshot Introduction.</h1> |
8 |
> |
<h1>JSR 166 Introduction.</h1> |
9 |
|
|
10 |
|
by <a href="http://gee.cs.oswego.edu/dl">Doug Lea</a> |
11 |
|
<p> |
12 |
|
|
13 |
< |
To join a mailing list discussing this JSR, go to: |
14 |
< |
<A HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest"> http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A> . |
15 |
< |
|
16 |
< |
<p> |
17 |
< |
<em> |
18 |
< |
Disclaimer - This prototype is experimental code developed as part of |
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 |
21 |
< |
specification, language and implementation are subject to change as a |
22 |
< |
result of your feedback. Because these features have not yet been |
23 |
< |
approved for addition to the Java language, there is no schedule for |
24 |
< |
their inclusion in a product. |
13 |
> |
This is maintenance repository of JSR166 specifications. For further |
14 |
> |
information, go to: <A |
15 |
> |
HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest"> |
16 |
> |
http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A>. |
17 |
> |
|
18 |
> |
<p><em>Note: The javadocs here do <em>not</em> include pre-existing |
19 |
> |
java classes (for example <tt>java.lang.Thread</tt>) that were changed |
20 |
> |
as part of the JSR166 spec. On the other hand, the javadocs here do |
21 |
> |
include some existing java.util Collection interfaces and classes that |
22 |
> |
are not part of the spec, but are included because some new methods |
23 |
> |
implement or inherit from their specifications. |
24 |
|
</em> |
25 |
|
|
26 |
< |
<p> JSR166 introduces package <tt>java.util.concurrent</tt> containing |
27 |
< |
utility classes commonly useful in concurrent programming. Like |
28 |
< |
package java.util, it includes a few small standardized extensible |
29 |
< |
frameworks, as well as some classes that provide useful functionality |
30 |
< |
and are otherwise tedious or difficult to implement. JSR-166 focusses |
31 |
< |
on breadth, prviding critical functionality useful across a wide range |
32 |
< |
of concurrent programming styles and applications, ranging from |
33 |
< |
low-level atomic operations, to customizable locks and synchronization |
34 |
< |
aids, to various concurrent data structures, to thread pools. |
35 |
< |
Descriptions of the main components may be found in the associated |
36 |
< |
package documentation. |
37 |
< |
|
38 |
< |
<p> JSR166 also includes a few changes and additions in packages |
39 |
< |
outside of java.util.concurrent. Here are brief descriptions. |
26 |
> |
<p>JSR-166 introduces package <tt>java.util.concurrent</tt> |
27 |
> |
containing utility classes commonly useful in concurrent |
28 |
> |
programming. Like package <tt>java.util</tt>, it includes a few small |
29 |
> |
standardized extensible frameworks, as well as other classes that |
30 |
> |
provide useful functionality and are otherwise tedious or difficult to |
31 |
> |
implement. |
32 |
> |
|
33 |
> |
<p>JSR-166 focusses on breadth, providing critical functionality |
34 |
> |
useful across a wide range of concurrent programming styles and |
35 |
> |
applications, ranging from low-level atomic operations, to |
36 |
> |
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> |
50 |
|
|
51 |
|
A basic (nonblocking) {@link java.util.Queue} interface extending |
52 |
< |
java.util.Collection is introduced into java.util. Existing class |
53 |
< |
java.util.LinkedList is adapted to support Queue, and a new |
54 |
< |
non-thread-safe {@link java.util.PriorityQueue} is added. |
55 |
< |
|
56 |
< |
<h2>Uncaught Exception Handlers</h2> |
57 |
< |
|
58 |
< |
The java.lang.Thread class is modified to allow per-thread |
59 |
< |
installation of handlers for uncaught exceptions. Ths optionally |
60 |
< |
disassociates these handlers from ThreadGroups, which has proven to be |
61 |
< |
too inflexible in many multithreaded programs. (Note that the |
62 |
< |
combination of features in JSR166 make ThreadGroups even less likely |
63 |
< |
to be used in most programs. Perhaps they will eventually be |
64 |
< |
deprecated.) |
65 |
< |
|
66 |
< |
<h2>High precision timing</h2> |
67 |
< |
|
68 |
< |
Method <tt>nanoTime</tt> is added to <tt>java.lang.System</tt>. It |
69 |
< |
provides a high-precision timing facility that is distinct from |
70 |
< |
and uncoordinated with <tt>System.currentTimeMillis</tt>. |
52 |
> |
{@link java.util.Collection} is introduced into |
53 |
> |
<tt>java.util</tt>. Existing class {@link java.util.LinkedList} is |
54 |
> |
adapted to support Queue, and a new non-thread-safe {@link |
55 |
> |
java.util.PriorityQueue} is added. |
56 |
> |
|
57 |
> |
<h2>Threads</h2> |
58 |
> |
|
59 |
> |
Three minor changes are introduced to the {@link java.lang.Thread} |
60 |
> |
class: |
61 |
> |
<ul> |
62 |
> |
<li> It now allows per-thread installation of handlers for uncaught |
63 |
> |
exceptions. Ths optionally disassociates handlers from ThreadGroups, |
64 |
> |
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 |
< |
The java.lang.ThreadLocal class now supports a means to remove a |
91 |
< |
ThreadLocal, which is needed in some thread-pool and worker-thread |
90 |
> |
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 |
92 |
|
designs. |
93 |
|
|
94 |
+ |
|
95 |
+ |
|
96 |
|
<hr> |
72 |
– |
<address><A HREF="http://gee.cs.oswego.edu/dl">Doug Lea</A></address> |
97 |
|
</body> |
98 |
|
</html> |