Swing app w/ HibernateUtil ThreadLocal - many threads?

allenjhbn · **Posted:** Fri Jul 07, 2006 9:21 am

I am using Hibernate 3.2 cr1 in a Swing app in a non-managed environment. I connect directly to my database - there is no EJB, J2EE, etc..

I am using the ubiquitous HibernateUtil code and am a bit confused about the ThreadLocal usage where the session is bound to the thread.

I want to use SwingWorker to spin off some new threads and make my UI more responsive - for example, retrieving data in a particular thread while using another thread for the UI or whatever. The same thing could happen when I persist transient instances back to the database. Heavy DB work should not happen in the EDT (Event Dispatch Thread).

This means that the thread and session that I use to get transient instances could be different than the thread and session I try to use to persist changes in those transient instances. As I understand it, this won't work in Hibernate.

My questions:
-If using ThreadLocal, is my only option to go with detached instances, so that persisting in a different session and thread will work, or am I misunderstanding the usage of ThreadLocal in HibernateUtil?

-Does it make sense to use detached instances in a non-managed Swing app environment?

-Does HibernateUtil, with ThreadLocal, preclude the use of multithreaded interface code?

Any advice greatly appreciated.

allen

Blackbrrd · **Joined:** Wed Sep 28, 2005 6:45 pm **Posts:** 56

I think you should use the simplest HibernateUtil if you are running in an unmanaged environment, but, I am a newbie, so I might be wrong.

In other words:

Code:

package util;

import org.hibernate.*;
import org.hibernate.cfg.*;

public class HibernateUtil {

    private static final SessionFactory sessionFactory;

    static {
        try {
            // Create the SessionFactory from hibernate.cfg.xml
            sessionFactory = new Configuration().configure().buildSessionFactory();
        } catch (Throwable ex) {
            // Make sure you log the exception, as it might be swallowed
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }

}

Look at the info in http://www.hibernate.org/hib_docs/v3/re ... tions.html

11.2.1. Non-managed environment

batmat · **Posted:** Fri Jul 07, 2006 9:54 am

In fact, there's no more need to use ThreadLocal object in HibernateUtil. It can be done automatically defining the property

Code:

<property name="current_session_context_class">thread</property>

in hibernate.cfg.xml

http://www.hibernate.org/hib_docs/v3/re ... pp-helpers

I'd say yes. You will have to work with detached instances and reattach them when you want to persist changes. Why don't you try to synchronize the hibernate code so you're sure you won't encounter concurrency problems ? Every threads would access the same threadsafe single object that will perform the db operations ?

allenjhbn · **Posted:** Fri Jul 07, 2006 11:58 am

batmat wrote:

In fact, there's no more need to use ThreadLocal object in HibernateUtil. It can be done automatically defining the property

Code:

<property name="current_session_context_class">thread</property>

in hibernate.cfg.xml

http://www.hibernate.org/hib_docs/v3/re ... pp-helpers

I'd say yes. You will have to work with detached instances and reattach them when you want to persist changes. Why don't you try to synchronize the hibernate code so you're sure you won't encounter concurrency problems ? Every threads would access the same threadsafe single object that will perform the db operations ?

Oh - okay. I'm familar w/ current_session_context_class = thread, but I though this was used to indicate to Hbn that I was using ThreadLocal in my code rather than it being a *replacement* for ThreadLocal. Looking at org.hibernate.context.ThreadLocalSessionContext, this makes sense now.

Your synchronization suggestion is great, but isn't that only half the issue?
Its not that I have 2 threads using the same session - I have 2 threads using 2 different sessions. If I want to get a persistent object in one session/thread, and then save updates to it in the other session/thread, what do I do? It looks like I can bind() my thread to a particular session, but how do I abstract this away in my DAO layer? Detached instances? ugh

batmat · **Posted:** Fri Jul 07, 2006 12:07 pm

Well yes, I'd say. Use detached instances in the upper layers than your service/dao ones. Then when you want to update it, reattach them with a lock(yourObject,LockMode.UPGRADE);

allenjhbn · **Posted:** Fri Jul 07, 2006 1:11 pm

batmat wrote:

Well yes, I'd say. Use detached instances in the upper layers than your service/dao ones. Then when you want to update it, reattach them with a lock(yourObject,LockMode.UPGRADE);

hhmmmmm....ok

But why would I use lock(yourObject,LockMode.UPGRADE) rather than update(yourObject)??

batmat · **Posted:** Fri Jul 07, 2006 2:48 pm

Well, you seem to be right : for an update, it seems the lock() is not to be done :

Quote:

After reconnection, to force a version check on data you aren't updating, you may call Session.lock() with LockMode.READ on any objects that might have been updated by another transaction. You don't need to lock any data that you are updating.

So update() should in fact be ok for you.

In fact, lock() has to do with the versionning system :
http://www.hibernate.org/hib_docs/v3/re ... e-detached

In your highly-concurrential environment, maybe you should consider using version property.

If you can detect modifs of your beans, in the case you're sure it has not been touched, there's also this interesting statement in the ref doc :

Quote:

You may also call lock() instead of update() and use LockMode.READ (performing a version check, bypassing all caches) if you are sure that the object has not been modified.

ZV_GP · **Joined:** Tue Sep 12, 2006 3:19 am **Posts:** 6

Hi Allen,

How did it eventually go ?
Anymore tips on Swing + Hibernate ?
How did you manage transactions/swingworker ?

Geert