| 1 |
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN"> |
| 2 |
<html> |
| 3 |
<head> |
| 4 |
<title>JSR 166 Introduction.</title> |
| 5 |
</head> |
| 6 |
|
| 7 |
<body bgcolor="#ffffee" vlink="#0000aa" link="#cc0000"> |
| 8 |
<h1>JSR 166 Introduction.</h1> |
| 9 |
|
| 10 |
by <a href="http://gee.cs.oswego.edu/dl">Doug Lea</a> |
| 11 |
<p> |
| 12 |
|
| 13 |
This is the final JSR166 specification submitted to JCP. 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 includes some existing java.util |
| 19 |
Collection interfaces and classes that are not part of the JSR-166 |
| 20 |
spec, but are included because JSR-166 methods implement or inherit |
| 21 |
from their specifications.</em> |
| 22 |
|
| 23 |
<p> JSR-166 introduces package <tt>java.util.concurrent</tt> |
| 24 |
containing utility classes commonly useful in concurrent |
| 25 |
programming. Like package <tt>java.util</tt>, it includes a few small |
| 26 |
standardized extensible frameworks, as well as other classes that |
| 27 |
provide useful functionality and are otherwise tedious or difficult to |
| 28 |
implement. |
| 29 |
|
| 30 |
<p>JSR-166 focusses on breadth, providing critical functionality |
| 31 |
useful across a wide range of concurrent programming styles and |
| 32 |
applications, ranging from low-level atomic operations, to |
| 33 |
customizable locks and synchronization aids, to various concurrent |
| 34 |
data structures, to high-level execution agents including thread |
| 35 |
pools. This diversity reflects the range of contexts in which |
| 36 |
developers of concurrent programs have been found to require or desire |
| 37 |
support not previously available in J2SE, which also keeping the |
| 38 |
resulting package small; providing only functionality that has been |
| 39 |
found to be worthwhile to standardize. |
| 40 |
|
| 41 |
<p>Descriptions and brief motivations for the main components may be |
| 42 |
found in the associated package documentation. JSR-166 also includes |
| 43 |
a few changes and additions in packages outside of |
| 44 |
java.util.concurrent. Here are brief descriptions. |
| 45 |
|
| 46 |
<h2>Queues</h2> |
| 47 |
|
| 48 |
A basic (nonblocking) {@link java.util.Queue} interface extending |
| 49 |
{@link java.util.Collection} is introduced into |
| 50 |
<tt>java.util</tt>. Existing class {@link java.util.LinkedList} is |
| 51 |
adapted to support Queue, and a new non-thread-safe {@link |
| 52 |
java.util.PriorityQueue} is added. |
| 53 |
|
| 54 |
<h2>Threads</h2> |
| 55 |
|
| 56 |
Three minor changes are introduced to the {@link java.lang.Thread} |
| 57 |
class: |
| 58 |
<ul> |
| 59 |
<li> It now allows per-thread installation of handlers for uncaught |
| 60 |
exceptions. Ths optionally disassociates handlers from ThreadGroups, |
| 61 |
which has proven to be too inflexible. (Note that the combination of |
| 62 |
features in JSR-166 make ThreadGroups even less likely to be used in |
| 63 |
most programs. Perhaps they will eventually be deprecated.) |
| 64 |
|
| 65 |
<li> Access checks are no longer required when a Thread interrupts |
| 66 |
<em>itself</em>. The <tt>interrupt</tt> method is the only way to |
| 67 |
re-assert a thread's interruption status (and in the case of |
| 68 |
self-interruption has no other effect than this). The check here |
| 69 |
previously caused unjustifiable and uncontrollable failures when |
| 70 |
restricted code invoked library code that must reassert interruption |
| 71 |
to correctly propagate status when encountering some |
| 72 |
<tt>InterruptedExceptions</tt>. |
| 73 |
<li> The <tt>destroy</tt> method, which has never been implemented, |
| 74 |
has finally been deprecated. This is just a spec change, reflecting |
| 75 |
the fact that that the reason it has never been implemented is that |
| 76 |
it was undesirable and unworkable. |
| 77 |
</ul> |
| 78 |
|
| 79 |
<h2>Timing</h2> |
| 80 |
|
| 81 |
Method <tt>nanoTime</tt> is added to {@link java.lang.System}. It |
| 82 |
provides a high-precision timing facility that is distinct from and |
| 83 |
uncoordinated with <tt>System.currentTimeMillis</tt>. |
| 84 |
|
| 85 |
<h2>Removing ThreadLocals</h2> |
| 86 |
|
| 87 |
The {@link java.lang.ThreadLocal} class now supports a means to remove |
| 88 |
a ThreadLocal, which is needed in some thread-pool and worker-thread |
| 89 |
designs. |
| 90 |
|
| 91 |
|
| 92 |
|
| 93 |
<hr> |
| 94 |
</body> |
| 95 |
</html> |
