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

[Steve Ebersole]

Also, why do you keep defining this in terms of Session, rather than
SessionFactory?


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
>> >> _______________________________________________
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>> >> hibernate-dev at lists.jboss.org
>> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev
>>
>