/*
* @(#)$Id$
*
* Copyright 2006-2008 Makoto YUI
*
* 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.
*
* Contributors:
* Makoto YUI - initial implementation
*/
package xbird.util.concurrent.lock;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
*
* <DIV lang="en"></DIV>
* <DIV lang="ja"></DIV>
*
* @author Maurice Herlihy
* @author Makoto YUI (yuin405+xbird@gmail.com)
*/
public final class FifoReadWriteLock implements IReadWriteLock {
private int readAcquires; // read acquires since start
private int readReleases; // read releses since start
private boolean writer; // writer present?
private final Lock metaLock; // short-term synchronization
private final Condition condition;
private final ILock readLock; // readers apply here
private final ILock writeLock; // writers apply here
public FifoReadWriteLock() {
readAcquires = readReleases = 0;
writer = false;
metaLock = new ReentrantLock();
condition = metaLock.newCondition();
readLock = new ReadLock();
writeLock = new WriteLock();
}
public ILock readLock() {
return readLock;
}
public ILock writeLock() {
return writeLock;
}
private final class ReadLock implements ILock {
ReadLock() {}
public void lock() {
metaLock.lock();
try {
readAcquires++;
while(writer) {
try {
condition.await();
} catch (InterruptedException ex) {
// do something application-specific
}
}
} finally {
metaLock.unlock();
}
}
public void unlock() {
metaLock.lock();
try {
readReleases++;
if(readAcquires == readReleases) {
condition.signalAll();
}
} finally {
metaLock.unlock();
}
}
public boolean isLocked() {
throw new UnsupportedOperationException();
}
}
private final class WriteLock implements ILock {
WriteLock() {}
public void lock() {
metaLock.lock();
try {
while(readAcquires != readReleases) {
try {
condition.await();
} catch (InterruptedException e) {
}
}
writer = true;
} finally {
metaLock.unlock();
}
}
public void unlock() {
writer = false;
}
public boolean isLocked() {
throw new UnsupportedOperationException();
}
}
}