1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.configuration2.sync;
18
19 import java.util.concurrent.locks.ReadWriteLock;
20 import java.util.concurrent.locks.ReentrantReadWriteLock;
21
22 /**
23 * <p>
24 * A special implementation of {@code Synchronizer} based on the JDK's {@code ReentrantReadWriteLock} class.
25 * </p>
26 * <p>
27 * This class manages a {@code ReadWriteLock} object internally. The methods of the {@code Synchronizer} interface are
28 * delegated to this lock. So this class behaves in the same way as documented for {@code ReentrantReadWriteLock}.
29 * </p>
30 * <p>
31 * Using this {@code Synchronizer} implementation is appropriate to make configuration objects thread-safe. This means
32 * that multiple threads can read configuration data in parallel; if one thread wants to update the configuration, this
33 * happens with an exclusive lock.
34 * </p>
35 *
36 * @since 2.0
37 */
38 public class ReadWriteSynchronizer implements Synchronizer {
39 /** The lock object used by this Synchronizer. */
40 private final ReadWriteLock lock;
41
42 /**
43 * Creates a new instance of {@code ReadWriteSynchronizer} and initializes it with the given lock object. This
44 * constructor can be used to pass a lock object which has been configured externally. If the lock object is
45 * <b>null</b>, a default lock object is created.
46 *
47 * @param l the lock object to be used (can be <b>null</b>)
48 */
49 public ReadWriteSynchronizer(final ReadWriteLock l) {
50 lock = l != null ? l : createDefaultLock();
51 }
52
53 /**
54 * Creates a new instance of {@code ReadWriteSynchronizer} and initializes it with a lock object of type
55 * {@code ReentrantReadWriteLock}.
56 */
57 public ReadWriteSynchronizer() {
58 this(null);
59 }
60
61 @Override
62 public void beginRead() {
63 lock.readLock().lock();
64 }
65
66 @Override
67 public void endRead() {
68 lock.readLock().unlock();
69 }
70
71 @Override
72 public void beginWrite() {
73 lock.writeLock().lock();
74 }
75
76 @Override
77 public void endWrite() {
78 lock.writeLock().unlock();
79 }
80
81 /**
82 * Returns a new default lock object which is used if no lock is passed to the constructor.
83 *
84 * @return the new default lock object
85 */
86 private static ReadWriteLock createDefaultLock() {
87 return new ReentrantReadWriteLock();
88 }
89 }