author | psandoz |
Wed, 03 Jul 2013 11:58:09 +0200 | |
changeset 18767 | 6214297bf27d |
parent 14325 | 622c473a21aa |
child 18790 | d25399d849bc |
permissions | -rw-r--r-- |
2 | 1 |
/* |
2 |
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
|
3 |
* |
|
4 |
* This code is free software; you can redistribute it and/or modify it |
|
5 |
* under the terms of the GNU General Public License version 2 only, as |
|
5506 | 6 |
* published by the Free Software Foundation. Oracle designates this |
2 | 7 |
* particular file as subject to the "Classpath" exception as provided |
5506 | 8 |
* by Oracle in the LICENSE file that accompanied this code. |
2 | 9 |
* |
10 |
* This code is distributed in the hope that it will be useful, but WITHOUT |
|
11 |
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
|
12 |
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
|
13 |
* version 2 for more details (a copy is included in the LICENSE file that |
|
14 |
* accompanied this code). |
|
15 |
* |
|
16 |
* You should have received a copy of the GNU General Public License version |
|
17 |
* 2 along with this work; if not, write to the Free Software Foundation, |
|
18 |
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
|
19 |
* |
|
5506 | 20 |
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
21 |
* or visit www.oracle.com if you need additional information or have any |
|
22 |
* questions. |
|
2 | 23 |
*/ |
24 |
||
25 |
/* |
|
26 |
* This file is available under and governed by the GNU General Public |
|
27 |
* License version 2 only, as published by the Free Software Foundation. |
|
28 |
* However, the following notice accompanied the original version of this |
|
29 |
* file: |
|
30 |
* |
|
31 |
* Written by Doug Lea with assistance from members of JCP JSR-166 |
|
32 |
* Expert Group and released to the public domain, as explained at |
|
9242
ef138d47df58
7034657: Update Creative Commons license URL in legal notices
dl
parents:
7518
diff
changeset
|
33 |
* http://creativecommons.org/publicdomain/zero/1.0/ |
2 | 34 |
*/ |
35 |
||
36 |
package java.util.concurrent; |
|
37 |
||
38 |
/** |
|
39 |
* An object that executes submitted {@link Runnable} tasks. This |
|
40 |
* interface provides a way of decoupling task submission from the |
|
41 |
* mechanics of how each task will be run, including details of thread |
|
42 |
* use, scheduling, etc. An <tt>Executor</tt> is normally used |
|
43 |
* instead of explicitly creating threads. For example, rather than |
|
44 |
* invoking <tt>new Thread(new(RunnableTask())).start()</tt> for each |
|
45 |
* of a set of tasks, you might use: |
|
46 |
* |
|
47 |
* <pre> |
|
48 |
* Executor executor = <em>anExecutor</em>; |
|
49 |
* executor.execute(new RunnableTask1()); |
|
50 |
* executor.execute(new RunnableTask2()); |
|
51 |
* ... |
|
52 |
* </pre> |
|
53 |
* |
|
54 |
* However, the <tt>Executor</tt> interface does not strictly |
|
55 |
* require that execution be asynchronous. In the simplest case, an |
|
56 |
* executor can run the submitted task immediately in the caller's |
|
57 |
* thread: |
|
58 |
* |
|
14325
622c473a21aa
8001575: Minor/sync/cleanup j.u.c with Dougs CVS - Oct 2012
dl
parents:
9242
diff
changeset
|
59 |
* <pre> {@code |
2 | 60 |
* class DirectExecutor implements Executor { |
14325
622c473a21aa
8001575: Minor/sync/cleanup j.u.c with Dougs CVS - Oct 2012
dl
parents:
9242
diff
changeset
|
61 |
* public void execute(Runnable r) { |
622c473a21aa
8001575: Minor/sync/cleanup j.u.c with Dougs CVS - Oct 2012
dl
parents:
9242
diff
changeset
|
62 |
* r.run(); |
622c473a21aa
8001575: Minor/sync/cleanup j.u.c with Dougs CVS - Oct 2012
dl
parents:
9242
diff
changeset
|
63 |
* } |
622c473a21aa
8001575: Minor/sync/cleanup j.u.c with Dougs CVS - Oct 2012
dl
parents:
9242
diff
changeset
|
64 |
* }}</pre> |
2 | 65 |
* |
66 |
* More typically, tasks are executed in some thread other |
|
67 |
* than the caller's thread. The executor below spawns a new thread |
|
68 |
* for each task. |
|
69 |
* |
|
14325
622c473a21aa
8001575: Minor/sync/cleanup j.u.c with Dougs CVS - Oct 2012
dl
parents:
9242
diff
changeset
|
70 |
* <pre> {@code |
2 | 71 |
* class ThreadPerTaskExecutor implements Executor { |
14325
622c473a21aa
8001575: Minor/sync/cleanup j.u.c with Dougs CVS - Oct 2012
dl
parents:
9242
diff
changeset
|
72 |
* public void execute(Runnable r) { |
622c473a21aa
8001575: Minor/sync/cleanup j.u.c with Dougs CVS - Oct 2012
dl
parents:
9242
diff
changeset
|
73 |
* new Thread(r).start(); |
622c473a21aa
8001575: Minor/sync/cleanup j.u.c with Dougs CVS - Oct 2012
dl
parents:
9242
diff
changeset
|
74 |
* } |
622c473a21aa
8001575: Minor/sync/cleanup j.u.c with Dougs CVS - Oct 2012
dl
parents:
9242
diff
changeset
|
75 |
* }}</pre> |
2 | 76 |
* |
77 |
* Many <tt>Executor</tt> implementations impose some sort of |
|
78 |
* limitation on how and when tasks are scheduled. The executor below |
|
79 |
* serializes the submission of tasks to a second executor, |
|
80 |
* illustrating a composite executor. |
|
81 |
* |
|
7518 | 82 |
* <pre> {@code |
2 | 83 |
* class SerialExecutor implements Executor { |
7518 | 84 |
* final Queue<Runnable> tasks = new ArrayDeque<Runnable>(); |
85 |
* final Executor executor; |
|
86 |
* Runnable active; |
|
2 | 87 |
* |
7518 | 88 |
* SerialExecutor(Executor executor) { |
89 |
* this.executor = executor; |
|
90 |
* } |
|
2 | 91 |
* |
7518 | 92 |
* public synchronized void execute(final Runnable r) { |
93 |
* tasks.offer(new Runnable() { |
|
94 |
* public void run() { |
|
95 |
* try { |
|
96 |
* r.run(); |
|
97 |
* } finally { |
|
98 |
* scheduleNext(); |
|
2 | 99 |
* } |
7518 | 100 |
* } |
101 |
* }); |
|
102 |
* if (active == null) { |
|
103 |
* scheduleNext(); |
|
2 | 104 |
* } |
7518 | 105 |
* } |
2 | 106 |
* |
7518 | 107 |
* protected synchronized void scheduleNext() { |
108 |
* if ((active = tasks.poll()) != null) { |
|
109 |
* executor.execute(active); |
|
2 | 110 |
* } |
7518 | 111 |
* } |
112 |
* }}</pre> |
|
2 | 113 |
* |
114 |
* The <tt>Executor</tt> implementations provided in this package |
|
115 |
* implement {@link ExecutorService}, which is a more extensive |
|
116 |
* interface. The {@link ThreadPoolExecutor} class provides an |
|
117 |
* extensible thread pool implementation. The {@link Executors} class |
|
118 |
* provides convenient factory methods for these Executors. |
|
119 |
* |
|
120 |
* <p>Memory consistency effects: Actions in a thread prior to |
|
121 |
* submitting a {@code Runnable} object to an {@code Executor} |
|
122 |
* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> |
|
123 |
* its execution begins, perhaps in another thread. |
|
124 |
* |
|
125 |
* @since 1.5 |
|
126 |
* @author Doug Lea |
|
127 |
*/ |
|
128 |
public interface Executor { |
|
129 |
||
130 |
/** |
|
131 |
* Executes the given command at some time in the future. The command |
|
132 |
* may execute in a new thread, in a pooled thread, or in the calling |
|
133 |
* thread, at the discretion of the <tt>Executor</tt> implementation. |
|
134 |
* |
|
135 |
* @param command the runnable task |
|
136 |
* @throws RejectedExecutionException if this task cannot be |
|
137 |
* accepted for execution. |
|
138 |
* @throws NullPointerException if command is null |
|
139 |
*/ |
|
140 |
void execute(Runnable command); |
|
141 |
} |