Java tutorial
/* * 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(); } } }