/**
*
* Copyright 2003-2004 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.geronimo.lock;
import java.util.HashSet;
import EDU.oswego.cs.dl.util.concurrent.ReadWriteLock;
import EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock;
/**
* Implementation based on the use of the util.concurrent package from Doug Lea.
*
* @version $Revision: 1.5 $ $Date: 2004/03/10 09:58:43 $
*/
public class ConcurrentInstanceLock implements InstanceLock {
private final ReadWriteLock lock;
private Object writer;
private final HashSet readers = new HashSet();
public ConcurrentInstanceLock() {
this.lock = new WriterPreferenceReadWriteLock();
}
public void sharedLock(Object context) throws InterruptedException {
lock.readLock().acquire();
synchronized (this) {
readers.add(context);
}
}
public void exclusiveLock(Object context) throws InterruptedException {
lock.writeLock().acquire();
synchronized (this) {
writer = context;
}
}
public synchronized void release(Object context) {
if (writer == context) {
writer = null;
lock.writeLock().release();
} else {
readers.remove(context);
lock.readLock().release();
}
}
public synchronized int getSharedCount() {
return readers.size();
}
}