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ModeShape implementation of the JCR API
There is a newer version: 5.4.1.Final
/*
 * ModeShape (http://www.modeshape.org)
 *
 * 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.modeshape.jcr.bus;

import java.util.Set;
import java.util.concurrent.CopyOnWriteArraySet;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import org.modeshape.common.collection.ring.RingBuffer;
import org.modeshape.common.collection.ring.RingBufferBuilder;
import org.modeshape.common.logging.Logger;
import org.modeshape.jcr.cache.change.ChangeSet;
import org.modeshape.jcr.cache.change.ChangeSetListener;

/**
 * Change bus implementation around a {@link org.modeshape.common.collection.ring.RingBuffer}
 * 
 * @author Randall Hauch ([email protected])
 * @author Horia Chiorean ([email protected])
 */
public final class RepositoryChangeBus implements ChangeBus {

    protected static final Logger LOGGER = Logger.getLogger(RepositoryChangeBus.class);

    private static final int DEFAULT_SIZE = 1 << 10; // 1024

    private final AtomicBoolean shutdown = new AtomicBoolean(true);
    /**
     * We use a lock for {@link #register(ChangeSetListener)}, {@link #registerInThread(ChangeSetListener)},
     * {@link #unregister(ChangeSetListener)}, {@link #start()} and {@link #shutdown()} to ensure that a single listener is
     * properly and atomcially added to either one of the maps. However, the {@link #notify(ChangeSet)} method only needs a
     * consistent snapshot of each of the maps (not a consistent snapshot of both), which is why we're using
     * concurrent maps (even though we're using a lock for registration).
     */
    private final Lock registrationLock = new ReentrantLock();
    private final Set inThreadListeners = new CopyOnWriteArraySet<>();
    private final RingBuffer ringBuffer;

    /**
     * Creates new change bus
     * 
     * @param repositoryName the repository name; may not be null
     * @param executor the {@link java.util.concurrent.ExecutorService} which will be used internally to submit workers to
     *        dispatching events to listeners.
     */
    public RepositoryChangeBus( String repositoryName,
                                ExecutorService executor ) {
        this.ringBuffer = RingBufferBuilder.withMultipleProducers(executor, new ChangeSetListenerConsumerAdapter())
                                           .ofSize(DEFAULT_SIZE).named(repositoryName).garbageCollect(true).build();
    }

    @Override
    public boolean hasObservers() {
        if (shutdown.get()) return false;
        return !inThreadListeners.isEmpty() || ringBuffer.hasConsumers();
    }

    @Override
    public boolean register( ChangeSetListener observer ) {
        if (observer == null || shutdown.get()) return false;
        try {
            registrationLock.lock();
            return ringBuffer.addConsumer(observer);
        } finally {
            registrationLock.unlock();
        }
    }

    @Override
    public boolean registerInThread( ChangeSetListener observer ) {
        if (observer == null || shutdown.get()) return false;
        try {
            registrationLock.lock();
            return inThreadListeners.add(observer);
        } finally {
            registrationLock.unlock();
        }
    }

    @Override
    public boolean unregister( ChangeSetListener observer ) {
        if (observer == null || shutdown.get()) return false;
        try {
            registrationLock.lock();
            return ringBuffer.remove(observer) || inThreadListeners.remove(observer);
        } finally {
            registrationLock.unlock();
        }
    }

    @Override
    public synchronized void start() throws Exception {
        shutdown.set(false);
    }

    @Override
    public synchronized void shutdown() {
        // This method is synchronized to make sure that 'start' and 'stop' are not called simultaneously ...
        if (shutdown.getAndSet(true)) {
            // It was already shutdown ...
            return;
        }

        try {
            registrationLock.lock();
            // Clear all of the in-thread listeners ...
            inThreadListeners.clear();
            // Shutdown the ring buffer waiting for running threads to complete
            ringBuffer.shutdown();
        } finally {
            registrationLock.unlock();
        }
    }

    @Override
    public void notify( ChangeSet changeSet ) {
        if (changeSet == null || !hasObservers()) return;
        if (shutdown.get()) {
            throw new IllegalStateException("Change bus has been already shut down, should not have any more observers");
        }

        // Add the change set into the buffer so it can be processed by the asynchronous listeners ...
        ringBuffer.add(changeSet);

        // And process all of the in-thread listeners ...
        for (ChangeSetListener listener : inThreadListeners) {
            listener.notify(changeSet);
        }
    }

    protected class ChangeSetListenerConsumerAdapter implements RingBuffer.ConsumerAdapter {
        @Override
        public boolean consume( ChangeSetListener consumer,
                                ChangeSet event,
                                long position,
                                long maxPosition ) {
            consumer.notify(event);
            return true;
        }

        @Override
        public void close( ChangeSetListener consumer ) {
            // nothing to do here
        }

        @Override
        public void handleException( ChangeSetListener consumer,
                                     Throwable t,
                                     ChangeSet entry,
                                     long position,
                                     long maxPosition ) {
            LOGGER.error(t, BusI18n.errorProcessingEvent, entry.toString(), position);
        }
    }
}