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Groovy: A powerful, dynamic language for the JVM

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/*
 * Copyright 2003-2010 the original author or authors.
 *
 * Licensed 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.codehaus.groovy.util;

import java.util.concurrent.locks.AbstractQueuedSynchronizer;

/**
 * A bit simplified lock designed to be inherited by.
 */
public class LockableObject extends AbstractQueuedSynchronizer {
    transient Thread owner;

    protected final boolean isHeldExclusively() {
        return getState() != 0 && owner == Thread.currentThread();
    }

    public final void lock() {
        if (compareAndSetState(0, 1))
            owner = Thread.currentThread();
        else
            acquire(1);
    }

    public final void unlock() {
        release(1);
    }

    protected final boolean tryAcquire(int acquires) {
        final Thread current = Thread.currentThread();
        int c = getState();
        if (c == 0) {
            if (compareAndSetState(0, acquires)) {
                owner = current;
                return true;
            }
        }
        else if (current == owner) {
            setState(c+ acquires);
            return true;
        }
        return false;
    }

    protected final boolean tryRelease(int releases) {
        int c = getState() - releases;
        if (Thread.currentThread() != owner)
            throw new IllegalMonitorStateException();
        boolean free = false;
        if (c == 0) {
            free = true;
            owner = null;
        }
        setState(c);
        return free;
    }
}