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 *     https://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 {@code ReentrantReadWriteLock} class.
025 * </p>
026 * <p>
027 * This class manages a {@code ReadWriteLock} object internally. The methods of the {@code Synchronizer} interface are
028 * delegated to this lock. So this class behaves in the same way as documented for {@code ReentrantReadWriteLock}.
029 * </p>
030 * <p>
031 * Using this {@code Synchronizer} implementation is appropriate to make configuration objects thread-safe. This means
032 * that multiple threads can read configuration data in parallel; if one thread wants to update the configuration, this
033 * happens with an exclusive lock.
034 * </p>
035 *
036 * @since 2.0
037 */
038public class ReadWriteSynchronizer implements Synchronizer {
039
040    /**
041     * Returns a new default lock object which is used if no lock is passed to the constructor.
042     *
043     * @return the new default lock object
044     */
045    private static ReadWriteLock createDefaultLock() {
046        return new ReentrantReadWriteLock();
047    }
048
049    /** The lock object used by this Synchronizer. */
050    private final ReadWriteLock lock;
051
052    /**
053     * Creates a new instance of {@code ReadWriteSynchronizer} and initializes it with a lock object of type
054     * {@code ReentrantReadWriteLock}.
055     */
056    public ReadWriteSynchronizer() {
057        this(null);
058    }
059
060    /**
061     * Creates a new instance of {@code ReadWriteSynchronizer} and initializes it with the given lock object. This
062     * constructor can be used to pass a lock object which has been configured externally. If the lock object is
063     * <strong>null</strong>, a default lock object is created.
064     *
065     * @param l the lock object to be used (can be <strong>null</strong>)
066     */
067    public ReadWriteSynchronizer(final ReadWriteLock l) {
068        lock = l != null ? l : createDefaultLock();
069    }
070
071    @Override
072    public void beginRead() {
073        lock.readLock().lock();
074    }
075
076    @Override
077    public void beginWrite() {
078        lock.writeLock().lock();
079    }
080
081    @Override
082    public void endRead() {
083        lock.readLock().unlock();
084    }
085
086    @Override
087    public void endWrite() {
088        lock.writeLock().unlock();
089    }
090}