    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}