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