Source Code Cross Referenced for ReaderWriterLockTest.java in  » IDE » DrJava » edu » rice » cs » util » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » IDE » DrJava » edu.rice.cs.util 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*BEGIN_COPYRIGHT_BLOCK
002:         *
003:         * Copyright (c) 2001-2007, JavaPLT group at Rice University (javaplt@rice.edu)
004:         * All rights reserved.
005:         * 
006:         * Redistribution and use in source and binary forms, with or without
007:         * modification, are permitted provided that the following conditions are met:
008:         *    * Redistributions of source code must retain the above copyright
009:         *      notice, this list of conditions and the following disclaimer.
010:         *    * Redistributions in binary form must reproduce the above copyright
011:         *      notice, this list of conditions and the following disclaimer in the
012:         *      documentation and/or other materials provided with the distribution.
013:         *    * Neither the names of DrJava, the JavaPLT group, Rice University, nor the
014:         *      names of its contributors may be used to endorse or promote products
015:         *      derived from this software without specific prior written permission.
016:         * 
017:         * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
018:         * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
019:         * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
020:         * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
021:         * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
022:         * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
023:         * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
024:         * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
025:         * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
026:         * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
027:         * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
028:         *
029:         * This software is Open Source Initiative approved Open Source Software.
030:         * Open Source Initative Approved is a trademark of the Open Source Initiative.
031:         * 
032:         * This file is part of DrJava.  Download the current version of this project
033:         * from http://www.drjava.org/ or http://sourceforge.net/projects/drjava/
034:         * 
035:         * END_COPYRIGHT_BLOCK*/
036:
037:        package edu.rice.cs.util;
038:
039:        import edu.rice.cs.drjava.DrJavaTestCase;
040:
041:        /** Attempts to test the correctness of the ReaderWriterLock class, which allows multiple reader and writer threads to
042:         * safely access a shared resource.  (Multiple readers can be active at a time, but only one writer can be active, 
043:         * during which time no readers can be active.)  This can be difficult to test because there is little control over 
044:         * how the threads are actually scheduled.
045:         * @version $Id: ReaderWriterLockTest.java 4255 2007-08-28 19:17:37Z mgricken $
046:         */
047:        public class ReaderWriterLockTest extends DrJavaTestCase {
048:
049:            protected ReaderWriterLock _lock;
050:
051:            /** Creates a new lock for the tests. */
052:            public void setUp() throws Exception {
053:                super .setUp();
054:                _lock = new ReaderWriterLock();
055:            }
056:
057:            // TO DO: Pull the next few lines out into a Semaphore class
058:
059:            /** Number of notifications expected before we actually notify. */
060:            private int _notifyCount = 0;
061:
062:            /** Object to provide semaphore-like synchronization. */
063:            private final Object _notifyObject = new Object();
064:
065:            /** Notifies the _notifyObject (semaphore) when the _notifyCount reaches 0.  (Decrements the count on each call.) */
066:            private void _notify() {
067:                synchronized (_notifyObject) {
068:                    _notifyCount--;
069:                    if (_notifyCount <= 0) {
070:                        _notifyObject.notify();
071:                        _notifyCount = 0;
072:                    }
073:                }
074:            }
075:
076:            /** Tests that multiple readers can run without causing deadlock. We can't really impose any ordering on their output.
077:             */
078:            public void testMultipleReaders() throws InterruptedException {
079:                final StringBuilder buf = new StringBuilder();
080:
081:                // Create three threads
082:                ReaderThread r1 = new PrinterReaderThread("r1 ", buf);
083:                ReaderThread r2 = new PrinterReaderThread("r2 ", buf);
084:                ReaderThread r3 = new PrinterReaderThread("r3 ", buf);
085:
086:                // Init the count
087:                _notifyCount = 3;
088:
089:                // Start the readers
090:                synchronized (_notifyObject) {
091:                    r1.start();
092:                    r2.start();
093:                    r3.start();
094:                    _notifyObject.wait();
095:                }
096:                //    String output = buf.toString();
097:                //    System.out.println(output);
098:            }
099:
100:            /** Tests that multiple writers run in mutually exclusive intervals without causing deadlock. */
101:            public void testMultipleWriters() throws InterruptedException {
102:                final StringBuilder buf = new StringBuilder();
103:
104:                // Create three threads
105:                WriterThread w1 = new PrinterWriterThread("w1 ", buf);
106:                WriterThread w2 = new PrinterWriterThread("w2 ", buf);
107:                WriterThread w3 = new PrinterWriterThread("w3 ", buf);
108:
109:                // Init the count
110:                _notifyCount = 3;
111:
112:                // Start the readers
113:                synchronized (_notifyObject) {
114:                    w1.start();
115:                    w2.start();
116:                    w3.start();
117:                    _notifyObject.wait();
118:                }
119:                String output = buf.toString();
120:                //System.out.println(output);
121:
122:                // Writer output should never be interspersed.
123:                assertTrue("w1 writes should happen in order", output
124:                        .indexOf("w1 w1 w1 ") != -1);
125:                assertTrue("w2 writes should happen in order", output
126:                        .indexOf("w2 w2 w2 ") != -1);
127:                assertTrue("w1 writes should happen in order", output
128:                        .indexOf("w3 w3 w3 ") != -1);
129:            }
130:
131:            /** Ensure that a single thread can perform multiple reads. */
132:            public void testReaderMultipleReads() throws InterruptedException {
133:                // Simulate a reader that performs multiple reads in one thread
134:                _lock.startRead();
135:                _lock.startRead();
136:                _lock.endRead();
137:                _lock.endRead();
138:
139:                // Test that a reading thread can perform an additional read even if
140:                //  a writing thread is waiting.
141:                _lock.startRead();
142:                Thread w = new Thread() {
143:                    public void run() {
144:                        synchronized (_lock) {
145:                            _lock.notifyAll();
146:                            _lock.startWrite();
147:                            // Waits here and releases _lock...
148:                            _lock.endWrite();
149:                        }
150:                    }
151:                };
152:                synchronized (_lock) {
153:                    w.start();
154:                    _lock.wait();
155:                }
156:                _lock.startRead();
157:                _lock.endRead();
158:                _lock.endRead();
159:            }
160:
161:            /** Ensure that a reading thread cannot perform a write. */
162:            public void testCannotWriteInARead() {
163:                try {
164:                    _lock.startRead();
165:                    _lock.startWrite();
166:                    fail("Should have caused an IllegalStateException!");
167:                } catch (IllegalStateException ise) {
168:                    // Good, that's what we want
169:                }
170:            }
171:
172:            /** Ensure that a writing thread cannot perform an additional write. */
173:            public void testCannotWriteInAWrite() {
174:                try {
175:                    _lock.startWrite();
176:                    _lock.startWrite();
177:                    fail("Should have caused an IllegalStateException!");
178:                } catch (IllegalStateException ise) {
179:                    // Good, that's what we want
180:                }
181:            }
182:
183:            /** Ensure that a writing thread cannot perform a read. */
184:            public void testCannotReadInAWrite() {
185:                try {
186:                    _lock.startWrite();
187:                    _lock.startRead();
188:                    fail("Should have caused an IllegalStateException!");
189:                } catch (IllegalStateException ise) {
190:                    // Good, that's what we want
191:                }
192:            }
193:
194:            /**
195:             * We would like to test the following schedule.
196:             *
197:             * <pre>
198:             * W1 |***********|
199:             * W2   |..........*****|
200:             * R1     |..............********|
201:             * R2       |............****|
202:             * W3         |...................***|
203:             * R3           |.....................****|
204:             * R4                |................*******|
205:             * R5                                   |***|
206:             * </pre>
207:             *
208:             * Key: "." means waiting, "*" means running
209:             *
210:             * This is next to impossible to set up in Java.  What we'd really
211:             * like is a unit-testing framework that allows us to easily specify
212:             * such a schedule in a test.  (Conveniently, Corky Cartwright has
213:             * applied for a Texas ATP grant to develop just such a framework.)
214:             *
215:             *
216:             * So, instead, we'll just set up these threads, let them run, and
217:             * enforce that no one interferes with output from a writer.
218:             */
219:            public void testMultipleReadersAndWriters()
220:                    throws InterruptedException {
221:                final StringBuilder buf = new StringBuilder();
222:
223:                // Create threads
224:                WriterThread w1 = new PrinterWriterThread("w1 ", buf);
225:                WriterThread w2 = new PrinterWriterThread("w2 ", buf);
226:                WriterThread w3 = new PrinterWriterThread("w3 ", buf);
227:
228:                ReaderThread r1 = new PrinterReaderThread("r1 ", buf);
229:                ReaderThread r2 = new PrinterReaderThread("r2 ", buf);
230:                ReaderThread r3 = new PrinterReaderThread("r3 ", buf);
231:                ReaderThread r4 = new PrinterReaderThread("r4 ", buf);
232:                ReaderThread r5 = new PrinterReaderThread("r5 ", buf);
233:
234:                // Init the count
235:                _notifyCount = 8;
236:
237:                // Start the readers
238:                synchronized (_notifyObject) {
239:                    w1.start();
240:                    w2.start();
241:                    r1.start();
242:                    r2.start();
243:                    w3.start();
244:                    r3.start();
245:                    r4.start();
246:                    r5.start();
247:                    _notifyObject.wait();
248:                }
249:                String output = buf.toString();
250:                //System.out.println(output);
251:
252:                // Writer output should never be interspersed.
253:                assertTrue("w1 writes should happen in order", output
254:                        .indexOf("w1 w1 w1 ") != -1);
255:                assertTrue("w2 writes should happen in order", output
256:                        .indexOf("w2 w2 w2 ") != -1);
257:                assertTrue("w1 writes should happen in order", output
258:                        .indexOf("w3 w3 w3 ") != -1);
259:            }
260:
261:            /** A reader thread. */
262:            public abstract class ReaderThread extends Thread {
263:                public abstract void read() throws Throwable;
264:
265:                public void run() {
266:                    _lock.startRead();
267:                    try {
268:                        read();
269:                    } catch (Throwable t) {
270:                        t.printStackTrace();
271:                    }
272:                    _lock.endRead();
273:                }
274:            }
275:
276:            /** A writer thread. */
277:            public abstract class WriterThread extends Thread {
278:                public abstract void write() throws Throwable;
279:
280:                public void run() {
281:                    _lock.startWrite();
282:                    try {
283:                        write();
284:                    } catch (Throwable t) {
285:                        t.printStackTrace();
286:                    }
287:                    _lock.endWrite();
288:                }
289:            }
290:
291:            /** A ReaderThread which repeatedly prints to a buffer. */
292:            public class PrinterReaderThread extends ReaderThread {
293:                PrintCommand _command;
294:
295:                public PrinterReaderThread(String msg, final StringBuilder buf) {
296:                    _command = new PrintCommand(msg, buf);
297:                }
298:
299:                public void read() {
300:                    _command.print();
301:                }
302:            }
303:
304:            /** A WriterThread which repeatedly prints to a buffer. */
305:            public class PrinterWriterThread extends WriterThread {
306:                PrintCommand _command;
307:
308:                public PrinterWriterThread(String msg, final StringBuilder buf) {
309:                    _command = new PrintCommand(msg, buf);
310:                }
311:
312:                public void write() {
313:                    _command.print();
314:                }
315:            }
316:
317:            /** Command pattern class to print to a buffer. */
318:            public class PrintCommand {
319:                /** Number of times to print */
320:                int _numIterations = 3;
321:                /** Number of milliseconds to wait between iterations */
322:                int _waitMillis = 5;
323:                /** Buffer to print to */
324:                final StringBuilder _buf;
325:                /** Message to print */
326:                final String _msg;
327:
328:                /** Creates a new command to print to a buffer during a read or write. */
329:                public PrintCommand(String msg, StringBuilder buf) {
330:                    _msg = msg;
331:                    _buf = buf;
332:                }
333:
334:                /** Prints the message to the buffer. */
335:                public void print() {
336:                    for (int i = 0; i < _numIterations; i++) {
337:                        _buf.append(_msg);
338:                        try {
339:                            Thread.sleep(_waitMillis);
340:                        } catch (InterruptedException e) {
341:                            _buf.append(e);
342:                        }
343:                    }
344:                    _notify();
345:                }
346:            }
347:        }
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