001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2.sync;
018
019import java.util.concurrent.locks.ReadWriteLock;
020import java.util.concurrent.locks.ReentrantReadWriteLock;
021
022/**
023 * <p>
024 * A special implementation of {@code Synchronizer} based on the JDK's
025 * {@code ReentrantReadWriteLock} class.
026 * </p>
027 * <p>
028 * This class manages a {@code ReadWriteLock} object internally. The methods of
029 * the {@code Synchronizer} interface are delegated to this lock. So this class
030 * behaves in the same way as documented for {@code ReentrantReadWriteLock}.
031 * </p>
032 * <p>
033 * Using this {@code Synchronizer} implementation is appropriate to make
034 * configuration objects thread-safe. This means that multiple threads can read
035 * configuration data in parallel; if one thread wants to update the
036 * configuration, this happens with an exclusive lock.
037 * </p>
038 *
039 * @version $Id: ReadWriteSynchronizer.java 1624601 2014-09-12 18:04:36Z oheger $
040 * @since 2.0
041 */
042public class ReadWriteSynchronizer implements Synchronizer
043{
044    /** The lock object used by this Synchronizer. */
045    private final ReadWriteLock lock;
046
047    /**
048     * Creates a new instance of {@code ReadWriteSynchronizer} and initializes
049     * it with the given lock object. This constructor can be used to pass a
050     * lock object which has been configured externally. If the lock object is
051     * <b>null</b>, a default lock object is created.
052     *
053     * @param l the lock object to be used (can be <b>null</b>)
054     */
055    public ReadWriteSynchronizer(ReadWriteLock l)
056    {
057        lock = (l != null) ? l : createDefaultLock();
058    }
059
060    /**
061     * Creates a new instance of {@code ReadWriteSynchronizer} and initializes
062     * it with a lock object of type {@code ReentrantReadWriteLock}.
063     */
064    public ReadWriteSynchronizer()
065    {
066        this(null);
067    }
068
069    @Override
070    public void beginRead()
071    {
072        lock.readLock().lock();
073    }
074
075    @Override
076    public void endRead()
077    {
078        lock.readLock().unlock();
079    }
080
081    @Override
082    public void beginWrite()
083    {
084        lock.writeLock().lock();
085    }
086
087    @Override
088    public void endWrite()
089    {
090        lock.writeLock().unlock();
091    }
092
093    /**
094     * Returns a new default lock object which is used if no lock is passed to
095     * the constructor.
096     *
097     * @return the new default lock object
098     */
099    private static ReadWriteLock createDefaultLock()
100    {
101        return new ReentrantReadWriteLock();
102    }
103}