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}