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 * @since 2.0
040 */
041public class ReadWriteSynchronizer implements Synchronizer
042{
043    /** The lock object used by this Synchronizer. */
044    private final ReadWriteLock lock;
045
046    /**
047     * Creates a new instance of {@code ReadWriteSynchronizer} and initializes
048     * it with the given lock object. This constructor can be used to pass a
049     * lock object which has been configured externally. If the lock object is
050     * <b>null</b>, a default lock object is created.
051     *
052     * @param l the lock object to be used (can be <b>null</b>)
053     */
054    public ReadWriteSynchronizer(final ReadWriteLock l)
055    {
056        lock = l != null ? l : createDefaultLock();
057    }
058
059    /**
060     * Creates a new instance of {@code ReadWriteSynchronizer} and initializes
061     * it with a lock object of type {@code ReentrantReadWriteLock}.
062     */
063    public ReadWriteSynchronizer()
064    {
065        this(null);
066    }
067
068    @Override
069    public void beginRead()
070    {
071        lock.readLock().lock();
072    }
073
074    @Override
075    public void endRead()
076    {
077        lock.readLock().unlock();
078    }
079
080    @Override
081    public void beginWrite()
082    {
083        lock.writeLock().lock();
084    }
085
086    @Override
087    public void endWrite()
088    {
089        lock.writeLock().unlock();
090    }
091
092    /**
093     * Returns a new default lock object which is used if no lock is passed to
094     * the constructor.
095     *
096     * @return the new default lock object
097     */
098    private static ReadWriteLock createDefaultLock()
099    {
100        return new ReentrantReadWriteLock();
101    }
102}