/*
* org.openmicroscopy.shoola.util.concur.TestSemaphoreSync
*
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* Copyright (C) 2006 University of Dundee. All rights reserved.
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*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
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* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
package org.openmicroscopy.shoola.util.concur;
//Java imports
//Third-party libraries
import junit.framework.TestCase;
//Application-internal dependencies
/**
* Verifies the safety of {@link Semaphore}.
* We test that <code>up</code> and <code>down</code> calls are serialized in
* the presence of multiple threads acting on the object.
*
* @see org.openmicroscopy.shoola.util.concur.ThreadSupport
* @author Jean-Marie Burel
* <a href="mailto:j.burel@dundee.ac.uk">j.burel@dundee.ac.uk</a>
* @author <br>Andrea Falconi
* <a href="mailto:a.falconi@dundee.ac.uk">
* a.falconi@dundee.ac.uk</a>
* @version 2.2
* <small>
* (<b>Internal version:</b> $Revision$ $Date$)
* </small>
* @since OME2.2
*/
public class TestSemaphoreSync
extends TestCase
{
private Semaphore sem; //Object to test.
private int semCount; //To transfer value from alternate flow.
private ThreadSupport threads; //To manage main/alt flows.
public void setUp()
{
threads = new ThreadSupport(new Runnable() { //Alternate flow.
public void run() { semCount = sem.getCount(); }
});
//NOTE: getCount() is sync. So if it is called while down/up is being
//executed in the main thread, then the alternate thread will have
//to wait until the lock is released. This is enough to test safety,
//there's no need to use more than two threads and verify all
//possible combinations of down and up.
sem = new Semaphore(1);
sem.register(new ControlFlowObserver() {
public void update(int checkPointID)
{ //Called w/in main thread.
if (checkPointID == Semaphore.LOCK_ACQUIRED) {
//down/up in progress. Spawn alt thread to retrieve count.
threads.startAltFlow(); //sem.getCount() will be called.
threads.pauseMainFlow();
//NOTE: Even though pausing the main flow doesn't guarantee
//that getCount() will be invoked in the mean time, the
//2-second delay used should in practice make this extremely
//likely to happen.
}
}
});
//NOTE: If getCount() gets executed b/f down/up modifies the counter,
//then we would also get the wrong value for semCount. In this case,
//we can deduce that locks were screwed up and thus fail the test.
//The test would be optimal if we could make sure that getCount() is
//actually invoked while down/up is being executed (in practice this is
//quite sure though). In any case, pausing the main thread is the best
//we can do as there's no way to tell whether a thread is waiting to
//acquire a lock.
}
public void testDown()
throws InterruptedException
{
sem.down();
threads.awaitAltFlow();
assertEquals("Concurrent access to count.", 0, semCount);
}
public void testDownTimeout()
throws InterruptedException
{
boolean decreased = sem.down(5000); //Timeout ignored b/c count is 1.
threads.awaitAltFlow();
assertTrue("Down should have returned true.", decreased);
assertEquals("Concurrent access to count.", 0, semCount);
}
public void testUp()
{
sem.up();
threads.awaitAltFlow();
assertEquals("Concurrent access to count.", 2, semCount);
}
}