Ensure NHibernate SessionFactory is only created once

Question

I have written an NHibernateSessionFactory class which holds a static Nhibernate ISessionFactory. This is used to make sure we only have one session factory, and the first t

Answer 1

I solved this using a Mutex when creating the SessionFactory. Does this look reasonable:

public class NhibernateSessionFactory : INhibernateSessionFactory
{
    private static ISessionFactory _sessionFactory;
    private static Mutex _mutex = new Mutex();  // <-- Added

    public ISession OpenSession()
    {
        if (_sessionFactory == null)
        {
            _mutex.WaitOne();              // <-- Added
            if (_sessionFactory == null)   // <-- Added
            {                              // <-- Added
                var cfg = Fluently.Configure().
                    Database(SQLiteConfiguration.Standard.ShowSql().UsingFile("Foo.db")).
                    Mappings(m => m.FluentMappings.AddFromAssemblyOf());
                _sessionFactory = cfg.BuildSessionFactory();
                BuildSchema(cfg);
            }                              // <-- Added
            _mutex.ReleaseMutex();         // <-- Added

        }
        return _sessionFactory.OpenSession();
    }

    private static void BuildSchema(FluentConfiguration configuration)
    {
        var sessionSource = new SessionSource(configuration);
        var session = sessionSource.CreateSession();
        sessionSource.BuildSchema(session);            
    }
}

Seems to work like a charm. But should I use lock instead?