maven-resolver-named-locks/src/main/java/org/eclipse/aether/named/support/AdaptedSemaphoreNamedLock.java

/*
 * 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;

import org.eclipse.aether.named.NamedLockKey;

/**
 * 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<Deque<Integer>> threadPerms;

    private final AdaptedSemaphore semaphore;

    public AdaptedSemaphoreNamedLock(
            final NamedLockKey key, final NamedLockFactorySupport factory, final AdaptedSemaphore semaphore) {
        super(key, factory);
        this.threadPerms = ThreadLocal.withInitial(ArrayDeque::new);
        this.semaphore = semaphore;
    }

    @Override
    protected boolean doLockShared(final long time, final TimeUnit unit) throws InterruptedException {
        Deque<Integer> 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<Integer> 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<Integer> 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);
        }
    }
}