1 /* ====================================================================
2 * License:
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 *
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 *
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in
13 * the documentation and/or other materials provided with the
14 * distribution.
15 *
16 * 3. The end-user documentation included with the redistribution,
17 * if any, must include the following acknowledgment:
18 * "This product includes software developed by
19 * Robert Half International (http://www.rhi.com/)."
20 * Alternately, this acknowledgment may appear in the software itself,
21 * if and wherever such third-party acknowledgments normally appear.
22 *
23 * 4. The names "Parc", "RHI", and "Robert Half International" must
24 * not be used to endorse or promote products derived from this
25 * software without prior written permission. For written
26 * permission, please contact pete.mckinstry@rhi.com.
27 *
28 * 5. Products derived from this software may not be called "PARC",
29 * nor may "PARC" appear in their name, without prior written
30 * permission of Robert Half International.
31 *
32 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
33 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
34 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
35 * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
36 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
37 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
38 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
39 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
40 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
41 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
42 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
43 * SUCH DAMAGE.
44 * ====================================================================
45 *
46 */
47 package com.rhi.architecture.threads;
48
49 import java.util.ArrayList;
50
51 /***
52 * Custom ThreadPool Implementation. The ThreadPool is started with predefined
53 * set of WorkerThreads which actually perform the work.
54 *
55 * This ThreadPool is suitable for scenarios work is split across
56 * mutiple threads and main thread waits for all the worker threads to
57 * finish and assigns work to all (or part) of worker threads.
58 *
59 * The ThreadPool can be asked to find a worked thread and assign work to it using
60 * execute method. Using join() method the caller will wait for all the worker
61 * threads to finish.
62 *
63 * IMPORTANT NOTE(S):
64 *
65 * 1. This ThreadPool is suitable for use by a single thread, not by mutliple
66 * threads/requests requesting ThreadPool to execute work.
67 * 2. It is the responsibility of the caller to make sure that it requests at
68 * maximum 'poolsize' amount of work to be performed by the ThreadPool.
69 * If no workers are free an RuntimeException is thrown.
70 *
71 * @author <a href="mailto:Chandra.Ilindra@rhi.com">Chandra Ilindra</a>
72 * @copyright 2002, Robert Half Int'l. All rights reserved.
73 *
74 * @version 1.0
75 */
76 public class ThreadPoolImpl implements ThreadPool {
77
78 // maintain a pool of worker threads.
79 ArrayList pool = null;
80
81 // pool size
82 int poolSize = 1;
83
84 /***
85 * Constructor - constructs a ThreadPool of given size. Constructs
86 * returns after all the threads have been created and started.
87 *
88 * @param size - size of the pool
89 *
90 * @since 1.0
91 */
92 public ThreadPoolImpl(int size) {
93
94 poolSize = size;
95 pool = new ArrayList(size);
96
97 for (int i = 0; i < size; i++) {
98 WorkerThread wThread = new WorkerThread(this);
99 wThread.setName("WorkerThread_" + i);
100 wThread.start();
101 pool.add(wThread);
102 }
103
104 }
105
106 /***
107 * Executes a given 'work'. Finds a free worker thread to execute the
108 * work - sets the work and notifies the worked thread to wake up
109 * and perform the work.
110 *
111 * @param work - work to be performed.
112 * @throws RuntimeException
113 * @since 1.0
114 */
115 public void execute(Runnable work) throws RuntimeException {
116
117 boolean allWorkersBusy = true;
118
119 for (int i = 0; i < poolSize; i++) {
120 WorkerThread wThread = (WorkerThread) pool.get(i);
121 if (wThread.noWork()) {
122 wThread.setWork(work);
123 synchronized (wThread) {
124 wThread.notify();
125 }
126 allWorkersBusy = false;
127 break;
128 }
129 }
130
131 if (allWorkersBusy) {
132 throw new RuntimeException("All Workers are busy could not perform the work.!");
133 }
134 }
135
136 /***
137 * Wait for all the worker threads to finish. If there are workers still
138 * performing the work, sleep for a second and then check again.
139 *
140 * @since 1.0
141 */
142 public void join() {
143
144 while (true) {
145 boolean allWorkersFree = true;
146 for (int i = 0; i < poolSize; i++) {
147 WorkerThread wThread = (WorkerThread) pool.get(i);
148 if (!wThread.noWork() && wThread.isAlive()) {
149 try {
150 allWorkersFree = false;
151 Thread.sleep(1000);
152 }
153 catch (InterruptedException e) {
154 // ignore exception and continue.
155 }
156 break; // come out of worker thread loop.
157 }
158 }
159
160 if (allWorkersFree) {
161 // enough of waiting, all finished, return.
162 break;
163 }
164 }
165
166 }
167
168 /***
169 * Mark all threads to shutdown and notify them, just in case they are
170 * sleeping.
171 *
172 * @since 1.0
173 */
174 public void close() {
175
176 for (int i = 0; i < poolSize; i++) {
177 WorkerThread wThread = (WorkerThread) pool.get(i);
178 wThread.markForShutDown();
179 synchronized (wThread) {
180 wThread.notify();
181 }
182 }
183
184 }
185 }
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