core/src/main/java/org/apache/oozie/service/MemoryLocksService.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.apache.oozie.service;

import org.apache.oozie.util.Instrumentable;
import org.apache.oozie.util.Instrumentation;
import org.apache.oozie.lock.LockToken;
import org.apache.oozie.lock.MemoryLocks;

import com.google.common.annotations.VisibleForTesting;
import org.apache.oozie.util.XLog;

/**
 * Service that provides in-memory locks.  Assumes no other Oozie servers are using the database.
 */
public class MemoryLocksService implements Service, Instrumentable {

    private static final XLog LOG = XLog.getLog(MemoryLocksService.class);

    public static enum Type {
        READ, WRITE
    }

    protected static final String INSTRUMENTATION_GROUP = "locks";
    private MemoryLocks locks;

    /**
     * Initialize the memory locks service
     *
     * @param services services instance.
     */
    @Override
    public void init(Services services) throws ServiceException {
        locks = new MemoryLocks();
    }

    /**
     * Destroy the memory locks service.
     */
    @Override
    public void destroy() {
        locks = null;
    }

    /**
     * Return the public interface for the memory locks services
     *
     * @return {@link MemoryLocksService}.
     */
    @Override
    public Class<? extends Service> getInterface() {
        return MemoryLocksService.class;
    }

    /**
     * Instruments the memory locks service.
     *
     * @param instr instance to instrument the memory locks service to.
     */
    public void instrument(Instrumentation instr) {
        final MemoryLocks finalLocks = this.locks;
        instr.addVariable(INSTRUMENTATION_GROUP, "locks", new Instrumentation.Variable<Long>() {
            public Long getValue() {
                return (long) finalLocks.size();
            }
        });
    }

    /**
     * Obtain a READ lock for a source.
     *
     * @param resource resource name.
     * @param wait time out in milliseconds to wait for the lock, -1 means no timeout and 0 no wait.
     * @return the lock token for the resource, or <code>null</code> if the lock could not be obtained.
     * @throws InterruptedException thrown if the thread was interrupted while waiting.
     */
    public LockToken getReadLock(final String resource, final long wait) throws InterruptedException {
        LOG.trace("Acquiring in-memory read lock. [resource={0};wait={1}]", resource, wait);
        return locks.getLock(resource, Type.READ, wait);
    }

    /**
     * Obtain a WRITE lock for a source.
     *
     * @param resource resource name.
     * @param wait time out in milliseconds to wait for the lock, -1 means no timeout and 0 no wait.
     * @return the lock token for the resource, or <code>null</code> if the lock could not be obtained.
     * @throws InterruptedException thrown if the thread was interrupted while waiting.
     */
    public LockToken getWriteLock(final String resource, final long wait) throws InterruptedException {
        LOG.trace("Acquiring in-memory write lock. [resource={0};wait={1}]", resource, wait);
        return locks.getLock(resource, Type.WRITE, wait);
    }

    @VisibleForTesting
    public MemoryLocks getMemoryLocks() {
        return locks;
    }
}