NHibernate SessionFactory Thread safe Issue

Question

So here is the problem. I have a common class library that holds all the repositories, domain and mapping files so the library can be reused within other web beased applications. Now within this class library there is a peiece of code that allows itself to create a session factory to be used in its repositories. Code looks something like this.

        private static ISessionFactory sessionFactory;
        private static Configuration configuration;

        public static Configuration Configuration()
        {
            if (configuration == null)
            {
                configuration = new Configuration().Configure();
            }
            return configuration;
        }

        private static ISessionFactory SessionFactory
        {
            get
            {
                if (sessionFactory == null)
                {
                    sessionFactory = Configuration().BuildSessionFactory();
                }
                return sessionFactory;
            }
        }

        public static ISession GetCurrentSession()
        {
            if (!CurrentSessionContext.HasBind(SessionFactory))
            {
                CurrentSessionContext.Bind(SessionFactory.OpenSession());
            }
            return SessionFactory.GetCurrentSession();
        }

So the repository calls the GetCurrentSession() method to get a ISession. Now this works fine but I am worried that it might not be thread safe. Can any one help me with an approach that will help me make it thread safe.

Few things to Note:

I have thought about configuring and building the SessionFactory in global.asax of the web applications on start event but the problem with this is that the common class library in question is used within 20 different applications so this will mean going to all the applications and updating the global.asax file now before I do this I wanted to put the question out there to see if there any other ways I can go about this. So that the common class library can configure its SessionFactory itself and yet be thread safe.

Thanks for reading this huge question. Will appericate any help.

Answer 1

The session factory is threadsafe, the session is not. Building the session factory needs to be protected:

    private static object lockObject = new object();

    private static ISessionFactory SessionFactory
    {
        get
        {
            lock (lockObject)
            {
                if (sessionFactory == null)
                {
                    sessionFactory = Configuration().BuildSessionFactory();
                }
                return sessionFactory;
            }
        }
    }

The session factory is created the first time a thread is requesting a session. This needs to be thread safe to avoid creating the session factory multiple times.

Creating the session by the session factory is thread safe, so you don't need to worry about that.

Answer 2

Sessions are not thread safe in NHibernate by design. So it should be ok as long as you have a session used by only one thread. You can have one NHibernate SessionFactory for multiple threads as long as you have a separate NHibernate session for each thread

for more info have a look at the below link:

https://forum.hibernate.org/viewtopic.php?p=2373236&sid=db537baa5a57e3968abdda5cceec2a24

Answer 3

I suggest use one session for each Request like this:

public ISession GetCurrentSession()
{
        HttpContext context = HttpContext.Current;

        var currentSession = context.Items["session"] as ISession;

        if( currentSession is null )
        {
             currentSession = SessionFactory.GetCurrentSession()
             context.Items["session"] = currentSession;
        }

        return currentSession;
}

Answer 4

Following on from the comment by Stefan Steinegger, I think it would be more efficient to add a null check immediately before the lock, that way you don't need to lock every time if the sessionFactory has already been initialized.

private static object lockObject = new object();

private static ISessionFactory SessionFactory
{
    get
    {
        if (sessionFactory != null)
        {
            return sessionFactory;
        }

        lock (lockObject)
        {
            if (sessionFactory == null)
            {
                sessionFactory = Configuration().BuildSessionFactory();
            }
            return sessionFactory;
        }
    }
}