Can Hibernate be implemented in a multithreading application

great_abe · **Joined:** Wed Jul 05, 2006 1:35 am **Posts:** 9

Hi Everyone,

Can Hibe be implement in a multi threading application? If yes
any best practices to do it?

thanks

abe

batmat · **Posted:** Wed Jul 05, 2006 4:23 am

You should have a look at the ref doc :
http://www.hibernate.org/hib_docs/v3/re ... tions.html

Remember that the Session object is not thread-safe, the SessionFactory is. So, take care about synchronizing your session object.

Also remember that the session objects should be very-short lived. In fact, this is a cache, so if you're working with different sessions that, say, have loaded the same objects, you will encounter some risks problems of sync in db (which versions will be persisted).

Moreover, if your environment is highly concurrencial, have also a look at the version field of hibernate (see the ref doc) and maybe also the pessimistic lock instead of the optimistic one.

great_abe · **Joined:** Wed Jul 05, 2006 1:35 am **Posts:** 9

Hi thanks for the reply..

In my implementation of threading.. each thread has its session.. is that right?

abe

batmat · **Posted:** Wed Jul 05, 2006 5:23 am

Yes, you must configure the SessionFactory to return a new session for each thread.

You can configure it using this : http://www.hibernate.org/hib_docs/v3/re ... properties

Code:

hibernate.current_session_context_class => thread

But as I said, you must take care that your sessions are short-lived. They're in fact a cache (the session is also called "first-level cache"), so could create some sync issues if not always short-lived.

great_abe · **Joined:** Wed Jul 05, 2006 1:35 am **Posts:** 9

Hi Again.. i am using a OpenSession to get a Session from my SessionFactory
is this the correct way to use it in a multi threading application

abe

batmat wrote:

Yes, you must configure the SessionFactory to return a new session for each thread.

You can configure it using this : http://www.hibernate.org/hib_docs/v3/re ... properties

Code:

hibernate.current_session_context_class => thread

But as I said, you must take care that your sessions are short-lived. They're in fact a cache (the session is also called "first-level cache"), so could create some sync issues if not always short-lived.

batmat · **Posted:** Wed Jul 05, 2006 7:06 am

great_abe wrote:

Hi Again.. i am using a OpenSession to get a Session from my SessionFactory
is this the correct way to use it in a multi threading application

I don't think so. Please have a look at the reference doc :
http://www.hibernate.org/hib_docs/v3/re ... orial.html

You should prefer retrieving it this way :

Code:

HibernateUtil.getSessionFactory().getCurrentSession();

The HibernateUtil helper class is given in the reference documentation of Hibernate :
http://www.hibernate.org/hib_docs/v3/re ... pp-helpers

Code:

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;
    }
}

Then, configure in hibernate.cfg.xml the thing I've spoken about before :

Code:

hibernate.current_session_context_class => thread

As explained in the doc, the meaning of the "current session" is depending on the configuration of this property "current_session_context_class". So give a special attention to it.

To finish, please don't forget to rate my answers by Yes or No it was useful below, as recalled in my signature. Thanks

alspaughb · **Posted:** Thu Jul 06, 2006 11:49 am

batmat wrote:

You should have a look at the ref doc :
http://www.hibernate.org/hib_docs/v3/re ... tions.html

Remember that the Session object is not thread-safe, the SessionFactory is. So, take care about synchronizing your session object.

Also remember that the session objects should be very-short lived. In fact, this is a cache, so if you're working with different sessions that, say, have loaded the same objects, you will encounter some risks problems of sync in db (which versions will be persisted).

Moreover, if your environment is highly concurrencial, have also a look at the version field of hibernate (see the ref doc) and maybe also the pessimistic lock instead of the optimistic one.

I'm using Hibernate in a Swing desktop application. Are the sessions required to be short-lived if you use the session-per-conversation pattern? The problem I see with closing the session is that lazy-loading of related objects and collections won't work if the session is closed. If you close the session, you have to make sure that all the objects that might be displayed are loaded before the session is closed and the objects are detached which means that you might be loading more objects into memory then necessary. I'm thinking that if you have long conversations, it is better to use the open-session-in-view pattern so you don't have to be constantly reloading the same objects into new short-lived sessions. The downside I see is that the application has to be prepared to handle exceptions when Hibernate detects that another user has modified an object while it is in your session. Is this correct?

Bruce