1 /***
2 * Redistribution and use of this software and associated documentation
3 * ("Software"), with or without modification, are permitted provided
4 * that the following conditions are met:
5 *
6 * 1. Redistributions of source code must retain copyright
7 * statements and notices. Redistributions must also contain a
8 * copy of this document.
9 *
10 * 2. Redistributions in binary form must reproduce the
11 * above copyright notice, this list of conditions and the
12 * following disclaimer in the documentation and/or other
13 * materials provided with the distribution.
14 *
15 * 3. The name "Exolab" must not be used to endorse or promote
16 * products derived from this Software without prior written
17 * permission of Exoffice Technologies. For written permission,
18 * please contact info@exolab.org.
19 *
20 * 4. Products derived from this Software may not be called "Exolab"
21 * nor may "Exolab" appear in their names without prior written
22 * permission of Exoffice Technologies. Exolab is a registered
23 * trademark of Exoffice Technologies.
24 *
25 * 5. Due credit should be given to the Exolab Project
26 * (http://www.exolab.org/).
27 *
28 * THIS SOFTWARE IS PROVIDED BY EXOFFICE TECHNOLOGIES AND CONTRIBUTORS
29 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
30 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
31 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
32 * EXOFFICE TECHNOLOGIES OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
33 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
34 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
35 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
36 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
37 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
38 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
39 * OF THE POSSIBILITY OF SUCH DAMAGE.
40 *
41 * Copyright 2005 (C) Exoffice Technologies Inc. All Rights Reserved.
42 *
43 * $Id: SerialTask.java,v 1.1 2005/08/30 05:38:56 tanderson Exp $
44 */
45 package org.exolab.jms.scheduler;
46
47 import org.apache.commons.logging.Log;
48 import org.apache.commons.logging.LogFactory;
49
50
51 /***
52 * A {@link Runnable} implementation which may only be executed serially by the
53 * {@link Scheduler}.
54 *
55 * @author <a href="mailto:tma@netspace.net.au">Tim Anderson</a>
56 * @version $Revision: 1.1 $ $Date: 2005/08/30 05:38:56 $
57 */
58 public class SerialTask implements Runnable {
59
60 /***
61 * The task to execute.
62 */
63 private Runnable _task;
64
65 /***
66 * The scheduler.
67 */
68 private final Scheduler _scheduler;
69
70 /***
71 * Determines if the task is currently active.
72 */
73 private boolean _active = false;
74
75 /***
76 * Determines if the task should stop.
77 */
78 private boolean _stop = false;
79
80 /***
81 * Determines if the task is scheduled to run.
82 */
83 private boolean _scheduled = false;
84
85 /***
86 * Determines if the task needs to be rescheduled.
87 */
88 private boolean _reschedule = false;
89
90 /***
91 * The logger.
92 */
93 private static final Log _log = LogFactory.getLog(SerialTask.class);
94
95
96 /***
97 * Construct a new <code>SerialTask</code>.
98 *
99 * @param task the task to execute
100 * @param scheduler the scheduler
101 */
102 public SerialTask(Runnable task, Scheduler scheduler) {
103 _task = task;
104 _scheduler = scheduler;
105 }
106
107 /***
108 * Schedule this to run.
109 * <p/>
110 * If the task is currently running, it will be scheduled after it has
111 * completed.
112 *
113 * @return <code>true</code> if the task was scheduled; <code>false</code>
114 * if the task is already scheduled, or is in the process of
115 * stopping
116 * @throws InterruptedException if the task can't be scheduled
117 */
118 public synchronized boolean schedule() throws InterruptedException {
119 if (_log.isDebugEnabled()) {
120 _log.debug("schedule() " + this);
121 }
122 boolean result = false;
123 if (!_stop && !_scheduled) {
124 if (_active) {
125 _reschedule = true;
126 } else {
127 _scheduled = true;
128 try {
129 _scheduler.execute(this);
130 } catch (InterruptedException exception) {
131 _scheduled = false;
132 throw exception;
133 }
134 }
135 result = true;
136 }
137 return result;
138 }
139
140 /***
141 * Run the task.
142 */
143 public void run() {
144 synchronized (this) {
145 if (_log.isDebugEnabled()) {
146 _log.debug("run() " + this);
147 }
148 if (_stop) {
149 if (_log.isDebugEnabled()) {
150 _log.debug("Scheduled task cancelled");
151 }
152 return;
153 }
154 if (_active) {
155 if (_log.isDebugEnabled()) {
156 _log.debug("Serial task already running, aborting");
157 }
158 throw new IllegalStateException("SerialTask already running");
159 }
160 _active = true;
161 _scheduled = false;
162 }
163 try {
164 _task.run();
165 } finally {
166 synchronized (this) {
167 _active = false;
168 if (_reschedule) {
169 try {
170 _reschedule = false;
171 _scheduled = true;
172 _scheduler.execute(this);
173 } catch (InterruptedException exception) {
174 _scheduled = false;
175 }
176 } else {
177 _scheduled = false;
178 }
179 notify();
180 }
181 }
182 }
183
184 /***
185 * Stop the task.
186 * <p/>
187 * This will wait for the task to complete before returning. If the task
188 * has been scheduled to run again, it will be cancelled.
189 */
190 public synchronized void stop() {
191 if (_log.isDebugEnabled()) {
192 _log.debug("stop() " + this);
193 }
194 _stop = true;
195 _reschedule = false;
196 _scheduled = false;
197 while (_active) {
198 try {
199 wait();
200 } catch (InterruptedException ignore) {
201 }
202 }
203 _reschedule = false;
204 _stop = false;
205 }
206
207 /***
208 * Returns a stringified form of this, for debugging purposes.
209 *
210 * @return a stringified form of this
211 */
212 public synchronized String toString() {
213 return "[stop=" + _stop + ", active=" + _active
214 + ", reschedule=" + _reschedule + ", scheduled=" + _scheduled
215 + "]";
216 }
217
218 }