Threadsafe persist in multithread environment?

[hurzeler]

I have a simple multithreaded action on JBoss 4.2.3, JRE 1.6.0_02, Seam 2.1 GA where I would like to harness the database connection pool of the container for performance reasons.

However an exception is thrown at the persist method call. I suspect this is because the EntityManager is not threadsafe.

How would I persist in a threadsafe way?

package com.risk.session;

import java.io.IOException;
import java.util.Calendar;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import org.jboss.seam.ScopeType;
import org.jboss.seam.annotations.Logger;
import org.jboss.seam.annotations.Name;
import org.jboss.seam.annotations.Scope;
import org.jboss.seam.annotations.Transactional;
import org.jboss.seam.framework.EntityController;
import org.jboss.seam.log.Log;

import com.risk.entity.TestEvent;

@Name("processor")
public class Processor extends EntityController
{

    /**
     * 
     */
    private static final long serialVersionUID = -8691085937149866076L;

    @Logger
    Log log;

    @Transactional
    public void process() throws IOException
    {
     log.info("Processing...");

     // Spawn threads to optimise the process
     ExecutorService threadExecutor = Executors.newFixedThreadPool(2);
     for (int i = 0; i < 2; i++)
     {
         threadExecutor.execute(new ProcessThread(i));
     }
    }

    class ProcessThread implements Runnable
    {

     private int threadNo;

     public ProcessThread(int threadNo)
     {
         this.threadNo = threadNo;
     }

     // This method is called when the thread runs
     public void run()
     {
         log.info("Thread #0 ...", threadNo);
         TestEvent event = new TestEvent();
         event.setDate(Calendar.getInstance().getTime());
         persist(event);
     }
    }
}

Here is the Entity:

package com.risk.entity;

import java.io.Serializable;
import java.util.Date;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;

@Entity
@Table(name = "tbl_testevent")
public class TestEvent implements Serializable, Idable
{

    /**
     * 
     */
    private static final long serialVersionUID = -7793151651824653553L;

    // seam-gen attributes (you should probably edit these)
    private Long id;

    private Date date;

 
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "testEvent_id_sequence")
    // name of the generator
    @SequenceGenerator(name = "testEvent_id_sequence", sequenceName = "TESTEVENT_ID_SEQ")
    public Long getId()
    {
     return id;
    }

    public void setId(Long id)
    {
     this.id = id;
    }

    /**
     * @return the creationDate
     */
    public Date getDate()
    {
     return date;
    }

    /**
     * @param creationDate
     *                the creationDate to set
     */
    public void setDate(Date date)
    {
     this.date = date;
    }

}

And the page:

<!DOCTYPE composition PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
                             "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<ui:composition xmlns="http://www.w3.org/1999/xhtml"
     xmlns:ui="http://java.sun.com/jsf/facelets"
     xmlns:h="http://java.sun.com/jsf/html">


          <h:form id="progressForm">
               <div class="actionButtons"><h:commandButton value="Process"
                    action="#{processor.process}" /></div>
          </h:form>

</ui:composition>

[hurzeler]

I think one needs to inject the EntityManagerFactory then make a new EntityManager in each thread.

package com.risk.session;

import java.io.IOException;
import java.util.Calendar;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;

import org.jboss.seam.annotations.In;
import org.jboss.seam.annotations.Logger;
import org.jboss.seam.annotations.Name;
import org.jboss.seam.annotations.Transactional;
import org.jboss.seam.log.Log;

import com.risk.entity.TestEvent;

@Name("processor")
public class Processor 
{

    /**
     * 
     */
    private static final long serialVersionUID = -8691085937149866076L;

    @Logger
    Log log;

    @In
    EntityManagerFactory entityManagerFactory;
    
    @Transactional
    public void process() throws IOException
    {
     log.info("Processing...");

     // Spawn threads to optimise the process
     ExecutorService threadExecutor = Executors.newFixedThreadPool(2);
     for (int i = 0; i < 2; i++)
     {
         threadExecutor.execute(new ProcessThread(i));
     }
    }

    class ProcessThread implements Runnable
    {

     private int threadNo;

     public ProcessThread(int threadNo)
     {
         this.threadNo = threadNo;
     }

     // This method is called when the thread runs
     public void run()
     {
            log.info("Thread #0 ...", threadNo);
         EntityManager em = entityManagerFactory.createEntityManager();
         TestEvent event = new TestEvent();
         event.setDate(Calendar.getInstance().getTime());
         em.persist(event);
     }
    }
}

The only trouble is that the entityManager resolves to null.

In commponent.xml I have:

<persistence:entity-manager-factory
          name="entityManagerFactory" persistence-unit-name="test" />
<persistence:managed-persistence-context
          name="entityManager" auto-create="true" entity-manager-factory="#{entityManagerFactory}" />

Just in case you wondering.

So why does the EntityManagerFactory resolve to null?

[balazska]

hy!

What was the solution?