1 package org.eclipse.aether.named.support;
2
3 /*
4 * Licensed to the Apache Software Foundation (ASF) under one
5 * or more contributor license agreements. See the NOTICE file
6 * distributed with this work for additional information
7 * regarding copyright ownership. The ASF licenses this file
8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
10 * with the License. You may obtain a copy of the License at
11 *
12 * http://www.apache.org/licenses/LICENSE-2.0
13 *
14 * Unless required by applicable law or agreed to in writing,
15 * software distributed under the License is distributed on an
16 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17 * KIND, either express or implied. See the License for the
18 * specific language governing permissions and limitations
19 * under the License.
20 */
21
22 import java.util.ArrayDeque;
23 import java.util.Deque;
24 import java.util.concurrent.TimeUnit;
25 import java.util.concurrent.locks.ReadWriteLock;
26
27 /**
28 * Named lock support implementation that is using {@link ReadWriteLock} instances. The adapted lock MUST SUPPORT
29 * reentrancy, non re-entrant locks will NOT work. It is the responsibility of an adapting lock, to ensure that
30 * above lock requirement stands.
31 */
32 public class ReadWriteLockNamedLock extends NamedLockSupport
33 {
34 private enum Step
35 {
36 /**
37 * Step when {@link ReadWriteLock#readLock()} was locked
38 */
39 SHARED,
40
41 /**
42 * Step when {@link ReadWriteLock#writeLock()} was locked
43 */
44 EXCLUSIVE
45 }
46
47 private final ThreadLocal<Deque<Step>> threadSteps;
48
49 private final ReadWriteLock readWriteLock;
50
51 public ReadWriteLockNamedLock( final String name, final NamedLockFactorySupport factory,
52 final ReadWriteLock readWriteLock )
53 {
54 super( name, factory );
55 this.threadSteps = ThreadLocal.withInitial( ArrayDeque::new );
56 this.readWriteLock = readWriteLock;
57 }
58
59 @Override
60 public boolean lockShared( final long time, final TimeUnit unit ) throws InterruptedException
61 {
62 Deque<Step> steps = threadSteps.get();
63 if ( readWriteLock.readLock().tryLock( time, unit ) )
64 {
65 steps.push( Step.SHARED );
66 return true;
67 }
68 return false;
69 }
70
71 @Override
72 public boolean lockExclusively( final long time, final TimeUnit unit ) throws InterruptedException
73 {
74 Deque<Step> steps = threadSteps.get();
75 if ( !steps.isEmpty() )
76 { // we already own shared or exclusive lock
77 if ( !steps.contains( Step.EXCLUSIVE ) )
78 {
79 return false; // Lock upgrade not supported
80 }
81 }
82 if ( readWriteLock.writeLock().tryLock( time, unit ) )
83 {
84 steps.push( Step.EXCLUSIVE );
85 return true;
86 }
87 return false;
88 }
89
90 @Override
91 public void unlock()
92 {
93 Deque<Step> steps = threadSteps.get();
94 if ( steps.isEmpty() )
95 {
96 throw new IllegalStateException( "Wrong API usage: unlock w/o lock" );
97 }
98 Step step = steps.pop();
99 if ( Step.SHARED == step )
100 {
101 readWriteLock.readLock().unlock();
102 }
103 else if ( Step.EXCLUSIVE == step )
104 {
105 readWriteLock.writeLock().unlock();
106 }
107 }
108 }