org.polymap.core.runtime.LockUtils.java Source code

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Here is the source code for org.polymap.core.runtime.LockUtils.java

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/* 
 * polymap.org
 * Copyright 2011, Polymap GmbH. All rights reserved.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 */
package org.polymap.core.runtime;

import java.util.concurrent.Callable;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * 
 *
 * @author <a href="http://www.polymap.de">Falko Brutigam</a>
 */
public class LockUtils {

    private static Log log = LogFactory.getLog(LockUtils.class);

    /**
     * Executes the given callable inside read lock of the given lock. The call()
     * method may aquire the write lock during execution. Both locks are released
     * after this method returns.
     * 
     * @param <V>
     * @param rwLock
     * @param task
     * @return The result of the given {@link #task}.
     * @throws Exception The exception from the {@link #task}.
     */
    public static <V> V withReadLock(ReentrantReadWriteLock rwLock, Callable<V> task) throws Exception {
        try {
            rwLock.readLock().lock();

            return task.call();
        } finally {
            if (rwLock.writeLock().isHeldByCurrentThread()) {
                rwLock.readLock().lock();
                rwLock.writeLock().unlock();
            }
            rwLock.readLock().unlock();
        }
    }

    /**
     * Executes the given runnable inside read lock of the given lock.
     *
     * @see #withReadLock(ReentrantReadWriteLock, Callable)
     * @throws Exception The exception from the {@link #task}.
     */
    public static void withReadLock(ReentrantReadWriteLock rwLock, final Runnable task) {
        try {
            withReadLock(rwLock, new Callable() {
                public Object call() throws Exception {
                    task.run();
                    return null;
                }
            });
        } catch (RuntimeException e) {
            throw e;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Simply *release* read lock and aquire write lock afterwards.
     * <p>
     * This is not a real upgrade as the real locl is <b>released</b>
     * before the write lock is aquired!
     * 
     * @param rwLock
     */
    public static void upgrade(ReentrantReadWriteLock rwLock) {
        rwLock.readLock().unlock();
        rwLock.writeLock().lock();
    }

}