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
26 /**
27 * Named lock support implementation that is using "adapted" semaphore (to be able to use semaphores not sharing common
28 * API).
29 */
30 public class AdaptedSemaphoreNamedLock extends NamedLockSupport
31 {
32 /**
33 * Wrapper for semaphore-like stuff, that do not share common ancestor. Semaphore must be created to support {@link
34 * Integer#MAX_VALUE} permissions.
35 */
36 public interface AdaptedSemaphore
37 {
38 boolean tryAcquire( int perms, long time, TimeUnit unit ) throws InterruptedException;
39
40 void release( int perms );
41 }
42
43 /**
44 * Count of permissions involved with "nop" locking. When required lock step is preceded with a step that already
45 * fulfils currently requested locking, no locking is needed. In other words, caller already possesses the access to
46 * lock protected resource. The "nop" locking is used to track proper "boxing" of lock/unlock calls.
47 */
48 private static final int NONE = 0;
49
50 /**
51 * Count of permissions involved with shared locking
52 */
53 private static final int SHARED = 1;
54
55 /**
56 * Count of permissions involved with exclusive locking
57 */
58 private static final int EXCLUSIVE = Integer.MAX_VALUE;
59
60 private final ThreadLocal<Deque<Integer>> threadPerms;
61
62 private final AdaptedSemaphore semaphore;
63
64 public AdaptedSemaphoreNamedLock( final String name, final NamedLockFactorySupport factory,
65 final AdaptedSemaphore semaphore )
66 {
67 super( name, factory );
68 this.threadPerms = ThreadLocal.withInitial( ArrayDeque::new );
69 this.semaphore = semaphore;
70 }
71
72 @Override
73 public boolean lockShared( final long time, final TimeUnit unit ) throws InterruptedException
74 {
75 Deque<Integer> perms = threadPerms.get();
76 if ( !perms.isEmpty() )
77 { // we already own shared or exclusive lock
78 perms.push( NONE );
79 return true;
80 }
81 if ( semaphore.tryAcquire( SHARED, time, unit ) )
82 {
83 perms.push( SHARED );
84 return true;
85 }
86 return false;
87 }
88
89 @Override
90 public boolean lockExclusively( final long time, final TimeUnit unit ) throws InterruptedException
91 {
92 Deque<Integer> perms = threadPerms.get();
93 if ( !perms.isEmpty() )
94 { // we already own shared or exclusive lock
95 if ( perms.contains( EXCLUSIVE ) )
96 {
97 perms.push( NONE );
98 return true;
99 }
100 else
101 {
102 return false; // Lock upgrade not supported
103 }
104 }
105 if ( semaphore.tryAcquire( EXCLUSIVE, time, unit ) )
106 {
107 perms.push( EXCLUSIVE );
108 return true;
109 }
110 return false;
111 }
112
113 @Override
114 public void unlock()
115 {
116 Deque<Integer> steps = threadPerms.get();
117 if ( steps.isEmpty() )
118 {
119 throw new IllegalStateException( "Wrong API usage: unlock w/o lock" );
120 }
121 int step = steps.pop();
122 if ( step > 0 )
123 {
124 semaphore.release( step );
125 }
126 }
127 }