/*
* JBoss, Home of Professional Open Source.
* Copyright 2012, Red Hat, Inc., and individual contributors
* as indicated by the @author tags. See the copyright.txt file in the
* distribution for a full listing of individual contributors.
*
* 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.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
package org.jboss.processFlow.knowledgeService;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.locks.ReentrantLock;
import javax.ejb.TransactionAttribute;
import javax.ejb.TransactionAttributeType;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import org.hibernate.LockMode;
import org.hibernate.Session;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.jboss.processFlow.util.JpaKnowledgeSessionPoolHelper;
/**
* The pool persists the knowledgeSession busy/available data structure into the table <code>SessionProcessXref</code>,
* so that we won't lost the session info after restart or hot-deploy. <br/>
*
* The pool implementation assumes that the one session per process instance strategy applied.
* <p>
* Since there are lot of database query/updating, the simple database tuning is create index for the sessionId and processInstanceId respectively (for example, on postgresql):
* <ul>
* <li>create index on sessionId: <code>[postgres]$ CREATE UNIQUE INDEX spx_sid_idx ON sessionprocessxref (sessionid);</code></li>
* <li>create index on processInstanceId: <code>[postgres]$ CREATE UNIQUE INDEX spx_pinstid_idx ON sessionprocessxref (processinstanceid);</code></li>
* </ul>
* </p>
*
* @author tanxu
* @date Mar 5, 2012
* @since
*
* 21 December 2012
* - Michal Valach added row-level pessimistic locking to ensure enterprise-wide concurrency on each process instance. thank you!
*/
@TransactionAttribute(TransactionAttributeType.REQUIRED)
public class JpaKnowledgeSessionPool extends JpaKnowledgeSessionPoolHelper implements IKnowledgeSessionPool {
private static final Logger logger = LoggerFactory.getLogger(JpaKnowledgeSessionPool.class);
public static final int STATUS_AVAILABLE = 0;
public static final int STATUS_BUSY = 1;
private LinkedList<Integer> availableSessions = new LinkedList<Integer>();
transient final ReentrantLock availableSessionsLock = new ReentrantLock();
public JpaKnowledgeSessionPool() {
super();
populateAvailableSessions();
}
private void populateAvailableSessions() {
EntityManager em = emf.createEntityManager();
try {
List<Integer> availableSessionIds = em
.createQuery("SELECT t.sessionId FROM SessionProcessXref t where t.status=:status")
.setParameter("status", STATUS_AVAILABLE).getResultList();
availableSessions.addAll(availableSessionIds);
logger.info("size of availableSessions after populate: {}", availableSessions.size());
}
finally {
em.close();
}
}
@Override
@TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED)
public Integer getAvailableSessionId() {
int sessionId = -1;
// query in memory for available sessionId rather than query from database
// 1) to improve the performance
// 2) to fix the optimistic issue of sessionInfo since it could return the same sessionId if query from database
if (availableSessions.size() > 0) {
availableSessionsLock.lock();
try {
sessionId = availableSessions.removeFirst();
}
finally {
availableSessionsLock.unlock();
}
}
return sessionId;
}
@Override
public boolean isBorrowed(Integer sessionId, String processId) {
EntityManager em = emf.createEntityManager();
try {
List<SessionProcessXref> sessions = em
.createQuery("FROM SessionProcessXref where sessionId=:sessionId and processId=:processId")
.setParameter("sessionId", sessionId).setParameter("processId", processId).getResultList();
return sessions.size() > 0;
}
finally {
em.close();
}
}
@Override
public void markAsBorrowed(Integer sessionId, String processId) {
EntityManager em = emf.createEntityManager();
try {
int rows = em.createQuery("UPDATE SessionProcessXref SET status=:status, processId =:processId WHERE sessionId=:sessionId")
.setParameter("status", STATUS_BUSY).setParameter("sessionId", sessionId)
.setParameter("processId", processId).executeUpdate();
if (rows == 0) {
SessionProcessXref xref = new SessionProcessXref();
xref.setProcessId(processId);
xref.setSessionId(sessionId);
xref.setStatus(STATUS_BUSY);
em.persist(xref);
}
}
finally {
em.flush();
em.close();
}
}
@Override
public void markAsReturned(Integer sessionId) {
EntityManager em = emf.createEntityManager();
try {
int rows = em.createQuery("UPDATE SessionProcessXref SET status=:status WHERE sessionId=:sessionId")
.setParameter("status", STATUS_AVAILABLE).setParameter("sessionId", sessionId).executeUpdate();
if (rows == 0) {
logger.warn("Failed to return the ksession: sessionId [{}] not found!");
}
else {
availableSessionsLock.lock();
try {
// Thank you Darren Osten
logger.debug("adding sessionid=" + sessionId + " to pool");
if (!availableSessions.contains(new Integer(sessionId))) {
availableSessions.addLast(new Integer(sessionId));
} else {
logger.warn("session " + sessionId + " already in pool");
}
}
finally {
availableSessionsLock.unlock();
}
}
}
finally {
em.close();
}
}
@Override
public String dumpSessionStatusInfo() {
StringBuilder sBuilder = new StringBuilder(
"dumpSessionStatusInfo()\nThe following is a list of sessions that are available for re-use by this knowledgeSessionService :\n");
EntityManager em = emf.createEntityManager();
try {
for (Integer sessionId : availableSessions) {
sBuilder.append(sessionId);
sBuilder.append(" ");
}
List<Integer> busySessions = em
.createQuery("SELECT t.sessionId FROM SessionProcessXref t where t.status=:status")
.setParameter("status", STATUS_BUSY).getResultList();
sBuilder.append("\n\nThe following is a list of sessions that are not yet available for re-use by this knowledgeSessionService :\n");
for (Integer ksessionId : busySessions) {
sBuilder.append(ksessionId);
sBuilder.append(" ");
}
}
finally {
em.close();
}
return sBuilder.toString();
}
public Integer getSessionId(Long pInstanceId) {
EntityManager em = emf.createEntityManager();
try {
Session session = (Session) em.getDelegate();
SessionProcessXref xref = (SessionProcessXref) session
.createQuery("SELECT xref FROM SessionProcessXref xref where xref.processInstanceId=:pInstanceId")
.setLockMode("xref", LockMode.PESSIMISTIC_WRITE)
.setParameter("pInstanceId", pInstanceId)
.uniqueResult();
if(xref == null)
throw new RuntimeException("getSessionId() unable to find SessionProcessXref in db for pInstanceId = "+pInstanceId);
return xref.getSessionId();
}
finally {
em.close();
}
}
}