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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.eclipse.aether.named.support;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.concurrent.TimeUnit;
/**
* Named lock support implementation that is using "adapted" semaphore (to be able to use semaphores not sharing common
* API).
*/
public class AdaptedSemaphoreNamedLock extends NamedLockSupport {
/**
* Wrapper for semaphore-like stuff, that do not share common ancestor. Semaphore must be created to support {@link
* Integer#MAX_VALUE} permissions.
*/
public interface AdaptedSemaphore {
boolean tryAcquire(int perms, long time, TimeUnit unit) throws InterruptedException;
void release(int perms);
}
/**
* Count of permissions involved with "nop" locking. When required lock step is preceded with a step that already
* fulfills currently requested locking, no locking is needed. In other words, caller already possesses the access
* to lock protected resource. The "nop" locking is used to track proper "boxing" of lock/unlock calls.
*/
private static final int NONE = 0;
/**
* Count of permissions involved with shared locking
*/
private static final int SHARED = 1;
/**
* Count of permissions involved with exclusive locking
*/
private static final int EXCLUSIVE = Integer.MAX_VALUE;
private final ThreadLocal> threadPerms;
private final AdaptedSemaphore semaphore;
public AdaptedSemaphoreNamedLock(
final String name, final NamedLockFactorySupport factory, final AdaptedSemaphore semaphore) {
super(name, factory);
this.threadPerms = ThreadLocal.withInitial(ArrayDeque::new);
this.semaphore = semaphore;
}
@Override
protected boolean doLockShared(final long time, final TimeUnit unit) throws InterruptedException {
Deque perms = threadPerms.get();
if (!perms.isEmpty()) { // we already own shared or exclusive lock
perms.push(NONE);
return true;
}
if (semaphore.tryAcquire(SHARED, time, unit)) {
perms.push(SHARED);
return true;
}
return false;
}
@Override
protected boolean doLockExclusively(final long time, final TimeUnit unit) throws InterruptedException {
Deque perms = threadPerms.get();
if (!perms.isEmpty()) { // we already own shared or exclusive lock
if (perms.contains(EXCLUSIVE)) {
perms.push(NONE);
return true;
} else {
throw new LockUpgradeNotSupportedException(this); // Lock upgrade not supported
}
}
if (semaphore.tryAcquire(EXCLUSIVE, time, unit)) {
perms.push(EXCLUSIVE);
return true;
}
return false;
}
@Override
protected void doUnlock() {
Deque steps = threadPerms.get();
if (steps.isEmpty()) {
throw new IllegalStateException("Wrong API usage: unlock without lock");
}
int step = steps.pop();
if (step > NONE) {
semaphore.release(step);
}
}
}