alfresco-community-repo/source/java/org/alfresco/schedule/ScheduledJobLockExecuter.java

/*
 * Copyright (C) 2005-2013 Alfresco Software Limited.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.

 * This program 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 General Public License for more details.

 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

 * As a special exception to the terms and conditions of version 2.0 of 
 * the GPL, you may redistribute this Program in connection with Free/Libre 
 * and Open Source Software ("FLOSS") applications as described in Alfresco's 
 * FLOSS exception.  You should have recieved a copy of the text describing 
 * the FLOSS exception, and it is also available here: 
 * http://www.alfresco.com/legal/licensing"
 */
package org.alfresco.schedule;

import org.alfresco.repo.lock.JobLockService;
import org.alfresco.repo.lock.LockAcquisitionException;
import org.alfresco.service.namespace.NamespaceService;
import org.alfresco.service.namespace.QName;
import org.alfresco.util.Pair;
import org.alfresco.util.VmShutdownListener.VmShutdownException;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.quartz.JobExecutionContext;
import org.quartz.JobExecutionException;

/**
 * This class encapsulates the {@link org.alfresco.repo.lock.JobLockService JobLockService}
 * usage in order to guarantee that a job is not executed
 * simultaneously in more than one node in a cluster. After instantiated passing
 * in constructor {@link org.alfresco.schedule.AbstractScheduledLockedJob job}
 * to be executed, as well as the name of the to be locked job and the
 * {@link org.alfresco.repo.lock.JobLockService JobLockService}, the execute
 * method of this class will execute the job taking care of all cluster aware lockings.
 * <p/>
 * This code is based on original code by Derek Hulley on
 * {@link org.alfresco.repo.content.cleanup.ContentStoreCleaner ContentStoreCleaner},
 * extracting the generic locking code in order to be reused and avoid code duplication.
 * 
 * @author Rui Fernandes
 * @since 4.1.5
 */
public class ScheduledJobLockExecuter
{
    private static final long LOCK_TTL = 30000L;

    private static Log logger = LogFactory.getLog(ScheduledJobLockExecuter.class.getName());
    private static ThreadLocal<Pair<Long, String>> lockThreadLocal = new ThreadLocal<Pair<Long, String>>();

    private final JobLockService jobLockService;
    private final QName lockQName;
    private final AbstractScheduledLockedJob job;

    /**
     * @param jobLockService the {@link JobLockService JobLockService}
     * @param name the name of the job to be used for the lock registry
     * @param job the {@link AbstractScheduledLockedJob job} to be executed
     */
    public ScheduledJobLockExecuter(JobLockService jobLockService, String name, AbstractScheduledLockedJob job)
    {
        this.jobLockService = jobLockService;
        this.lockQName = QName.createQName(NamespaceService.SYSTEM_MODEL_1_0_URI, name);
        this.job = job;
    }

    /**
     * It will execute the {@link AbstractScheduledLockedJob job} passed on
     * instantiation taking care of all cluster aware lockings.
     * 
     * @param jobContext the usual quartz job context
     * @throws JobExecutionException        thrown if the job fails to execute
     */
    public void execute(JobExecutionContext jobContext) throws JobExecutionException
    {
        try
        {
            if (logger.isDebugEnabled())
            {
                logger.debug(String.format("   Job %s started.", lockQName.getLocalName()));
            }
            refreshLock();
            job.executeJob(jobContext);
            if (logger.isDebugEnabled())
            {
                logger.debug(String.format("   Job %s completed.", lockQName.getLocalName()));
            }
        }
        catch (LockAcquisitionException e)
        {
            // Job being done by another process
            if (logger.isDebugEnabled())
            {
                logger.debug(String.format("   Job %s already underway.", lockQName.getLocalName()));
            }
        }
        catch (VmShutdownException e)
        {
            // Aborted
            if (logger.isDebugEnabled())
            {
                logger.debug(String.format("   Job %s aborted.", lockQName.getLocalName()));
            }
        }
        finally
        {
            releaseLock();
        }
    }

    /**
     * Lazily update the job lock
     */
    private void refreshLock()
    {
        Pair<Long, String> lockPair = lockThreadLocal.get();
        if (lockPair == null)
        {
            String lockToken = jobLockService.getLock(lockQName, LOCK_TTL);
            Long lastLock = new Long(System.currentTimeMillis());
            // We have not locked before
            lockPair = new Pair<Long, String>(lastLock, lockToken);
            lockThreadLocal.set(lockPair);
        }
        else
        {
            long now = System.currentTimeMillis();
            long lastLock = lockPair.getFirst().longValue();
            String lockToken = lockPair.getSecond();
            // Only refresh the lock if we are past a threshold
            if (now - lastLock > (long) (LOCK_TTL / 2L))
            {
                jobLockService.refreshLock(lockToken, lockQName, LOCK_TTL);
                lastLock = System.currentTimeMillis();
                lockPair = new Pair<Long, String>(lastLock, lockToken);
                lockThreadLocal.set(lockPair);
            }
        }
    }

    /**
     * Release the lock after the job completes
     */
    private void releaseLock()
    {
        Pair<Long, String> lockPair = lockThreadLocal.get();
        if (lockPair != null)
        {
            // We can't release without a token
            try
            {
                jobLockService.releaseLock(lockPair.getSecond(), lockQName);
            }
            finally
            {
                // Reset
                lockThreadLocal.set(null);
            }
        }
        // else: We can't release without a token
    }
}