[hibernate-dev] Lambda usage to run a code block in an isolated transaction

[Sanne Grinovero]

On 14 September 2016 at 21:02, Steve Ebersole <steve at hibernate.org> wrote:
> Also, why do you keep defining this in terms of Session, rather than
> SessionFactory?

I mentioned that same doubt in my first email of this thread.
I think I prefer Session as that's what people interact with most of
the time, and it's a better choice if we opt to make this a nested
transaction of the current one; if it's meant to be totally
independent yes then we should probably consider the SF.

>
>
> On Wed, Sep 14, 2016 at 3:01 PM Steve Ebersole <steve at hibernate.org> wrote:
>>
>> "Better" according to whom? ;)
>>
>> I personally very much dislike the kind of API explosion this kind of
>> thing leads to.
>>
>>
>> On Wed, Sep 14, 2016 at 2:59 PM Sanne Grinovero <sanne at hibernate.org>
>> wrote:
>>>
>>> On 14 September 2016 at 20:32, Steve Ebersole <steve at hibernate.org>
>>> wrote:
>>> > The problem with "execute in isolation" here is that the "isolation"
>>> > aspect
>>> > refers to being isolated from any current transaction.  It says nothing
>>> > about whether that stuff-to-execute should itself be transacted.  This
>>> > is
>>> > why, for example, you see IsolationDelegate accept a `transacted`
>>> > boolean
>>> > argument.
>>> >
>>> > How would you propose we pass such a flag in this case?  Or are you
>>> > proposing that this always start a (new) transaction?
>>>
>>> I had only the (new) transaction case in mind, but sure you could add
>>> a `transacted` boolean parameter.
>>>
>>> Or we make it explicit with a better method name:
>>>
>>> s.executeInSubtransaction( session -> session.save(...) );
>>>
>>> Thanks,
>>> Sanne
>>>
>>>
>>> >
>>> > On Wed, Sep 14, 2016 at 1:39 PM Sanne Grinovero <sanne at hibernate.org>
>>> > wrote:
>>> >>
>>> >> Today porting some benchmark code to Hibernate ORM 5.2 I had several
>>> >> difficulties around the fact that the code now needs to be different
>>> >> depending on transactions being container managed or not.
>>> >>
>>> >> My goal was to have a single benchmark test which I could compile once
>>> >> and run in either JavaSE or CMT; with some help from Steve I figured
>>> >> the necessary incantations out but ... it looks very unpractical.
>>> >>
>>> >> One way is to use an isolation delegate, which looks like this:
>>> >>
>>> >> final SessionImplementor session = (SessionImplementor) s;
>>> >>
>>> >>
>>> >> session.getTransactionCoordinator().createIsolationDelegate().delegateWork(
>>> >>    new WorkExecutorVisitable() {
>>> >>       @ Override
>>> >>       public Object accept(WorkExecutor executor, Connection
>>> >> connection) throws SQLException {
>>> >>          /// Some work with PreparedStatement on Connection..
>>> >>       }
>>> >> }, true );
>>> >>
>>> >> This worked fine for some raw SQL used for the benchmark
>>> >> initialization, but in another case I'd prefer to use the Session API
>>> >> rather than dealing with PreparedStatements and native connections;
>>> >> it looks like we don't have an equivalent "run code in isolation" for
>>> >> the Session ?
>>> >>
>>> >> It would be great if I could just pass a lambda to a Session and have
>>> >> this executed on a "child Session" in the scope of a "child
>>> >> Transaction", or just start and commit a transaction if there isn't
>>> >> one.
>>> >>
>>> >> s.executeInIsolation( session -> session.save(...) );
>>> >>
>>> >> So I'd expect that details like how to begin the transaction, how it
>>> >> should be committed (or rolled back in case of exceptions), how to
>>> >> lookup a TransactionManager, and especially how to not leak resources
>>> >> should be handled for the user.
>>> >>
>>> >> Obviously the inner Session instance is a different one than the
>>> >> outer, so any data returned by this block should be considered
>>> >> detached; maybe this limitation would be clearer if the method was
>>> >> hosted on SessionFactory or StatelessSession instead?
>>> >> Although it wouldn't necessarily have the limitations of a
>>> >> StalessSession, and it would be nice to have the inner transaction
>>> >> behave as a nested one when there's already one in the host Session.
>>> >>
>>> >> Looking forward for comments and improvement ideas :)
>>> >>
>>> >> Thanks,
>>> >> Sanne
>>> >> _______________________________________________
>>> >> hibernate-dev mailing list
>>> >> hibernate-dev at lists.jboss.org
>>> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev