NHibernate并发更新问题

Question

I'm currently testing concurrent update situations for my c#/NHibernate application. In the hibernate-configuration command_timeout is set 1 second for testing purposes. I use the hibernate version in the mapping file.

Here is the code for testing:

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            MyHibernateConnector hc = new MyHibernateConnector(); // 1 usage see below; also provides some other hibernate related methods
            MyHibernateConfig myhibconfig = new MyHibernateConfig(); // reads and holds hibernate configuration
            hc.setHibernateConfig(myhibconfig);

            ISession session = hc.getSessionAndStartTransaction();
            // getSessionAndStartTransaction() does the following:
            // - on first call: reads the hibernate configuration and builds the SessionFactory
            // - gets the session as follows:
            //   ISession session;
            //   if (CurrentSessionContext.HasBind(sf))
            //   {
            //       session = sf.GetCurrentSession();
            //   }
            //   else
            //   {
            //       session = sf.OpenSession();
            //       CurrentSessionContext.Bind(session);
            //   }
            // - and does session.BeginTransaction();

            MyClass obj;
            IQuery q = session.CreateQuery("select mc from MyClass as mc where mc.ID = ?");
            q.SetInt64(0, 60);

            l = q.List<MyClass>();
            if (l.Count > 0)
                obj = l[0];

            session.Transaction.Rollback();

            // now update obj in another application with autocommit off and do not commit or rollback

/* breakpont is set here */            session = hc.getSessionAndStartTransaction();

            try
            {
                session.Lock(obj, LockMode.Upgrade);
            } catch (Exception e)
            {
                try
                {
                    session.Transaction.Rollback();
                }
                catch (Exception e2)
                {
                    Type t = e2.GetType();
                }
            }
            // ...
        }
    }
}

On session.Lock(obj, LockMode.Upgrade) an exception ( GenericADOException ) is thrown as expected with message:

could not lock: … for update

If I now catch this exception and try to do an ISession.Transaction.Rollback() a TransactionException is thrown.

I would have expected that a rollback is the appropriate action to resolve concurrent update situations. Is this not so ? And what would be the appropriate action ? What is the state of the transaction after the TransactionException ?

I use NHibernate version 5.1.0.0 and MySql.Data version 6.10.7.0. Hibernate property dialect is NHibernate.Dialect.MySQL55InnoDBDialect .

Answer 1

After some more experimenting I think I found a solution - or should I better say a workaround: The ISession.Connection is closed after timeout occured on session.Lock(obj, LockMode.Upgrade) , so open it again before the rollback:

if (session.Connection.State.Equals(ConnectionState.Closed)) // <- !!!
    session.Connection.Open();
session.Transaction.Rollback();

This works and I could do further transactions with the same session.

Why the connection is closed in the first place remains a mystery to me!

And I wonder if this behaviour is common to other (all?) underlying DBMS and/or drivers.