1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 */
19 package org.eclipse.aether.named.support;
20
21 import java.util.ArrayDeque;
22 import java.util.Deque;
23 import java.util.concurrent.TimeUnit;
24
25 /**
26 * Named lock support implementation that is using "adapted" semaphore (to be able to use semaphores not sharing common
27 * API).
28 */
29 public class AdaptedSemaphoreNamedLock extends NamedLockSupport {
30 /**
31 * Wrapper for semaphore-like stuff, that do not share common ancestor. Semaphore must be created to support {@link
32 * Integer#MAX_VALUE} permissions.
33 */
34 public interface AdaptedSemaphore {
35 boolean tryAcquire(int perms, long time, TimeUnit unit) throws InterruptedException;
36
37 void release(int perms);
38 }
39
40 /**
41 * Count of permissions involved with "nop" locking. When required lock step is preceded with a step that already
42 * fulfills currently requested locking, no locking is needed. In other words, caller already possesses the access
43 * to lock protected resource. The "nop" locking is used to track proper "boxing" of lock/unlock calls.
44 */
45 private static final int NONE = 0;
46
47 /**
48 * Count of permissions involved with shared locking
49 */
50 private static final int SHARED = 1;
51
52 /**
53 * Count of permissions involved with exclusive locking
54 */
55 private static final int EXCLUSIVE = Integer.MAX_VALUE;
56
57 private final ThreadLocal<Deque<Integer>> threadPerms;
58
59 private final AdaptedSemaphore semaphore;
60
61 public AdaptedSemaphoreNamedLock(
62 final String name, final NamedLockFactorySupport factory, final AdaptedSemaphore semaphore) {
63 super(name, factory);
64 this.threadPerms = ThreadLocal.withInitial(ArrayDeque::new);
65 this.semaphore = semaphore;
66 }
67
68 @Override
69 protected boolean doLockShared(final long time, final TimeUnit unit) throws InterruptedException {
70 Deque<Integer> perms = threadPerms.get();
71 if (!perms.isEmpty()) { // we already own shared or exclusive lock
72 perms.push(NONE);
73 return true;
74 }
75 if (semaphore.tryAcquire(SHARED, time, unit)) {
76 perms.push(SHARED);
77 return true;
78 }
79 return false;
80 }
81
82 @Override
83 protected boolean doLockExclusively(final long time, final TimeUnit unit) throws InterruptedException {
84 Deque<Integer> perms = threadPerms.get();
85 if (!perms.isEmpty()) { // we already own shared or exclusive lock
86 if (perms.contains(EXCLUSIVE)) {
87 perms.push(NONE);
88 return true;
89 } else {
90 throw new LockUpgradeNotSupportedException(this); // Lock upgrade not supported
91 }
92 }
93 if (semaphore.tryAcquire(EXCLUSIVE, time, unit)) {
94 perms.push(EXCLUSIVE);
95 return true;
96 }
97 return false;
98 }
99
100 @Override
101 protected void doUnlock() {
102 Deque<Integer> steps = threadPerms.get();
103 if (steps.isEmpty()) {
104 throw new IllegalStateException("Wrong API usage: unlock without lock");
105 }
106 int step = steps.pop();
107 if (step > NONE) {
108 semaphore.release(step);
109 }
110 }
111 }