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

Most transaction systems do not support nested transactions On Wed, Sep 14, 2016 at 3:13 PM Sanne Grinovero <sanne(a)hibernate.org&gt; wrote: > On 14 September 2016 at 21:02, Steve Ebersole <steve(a)hibernate.org&gt; > 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(a)hibernate.org&gt; > 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(a)hibernate.org&gt; > >> wrote: > >>> > >>> On 14 September 2016 at 20:32, Steve Ebersole <steve(a)hibernate.org&gt; > >>> 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(a)hibernate.org&gt; > >>> > 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(a)lists.jboss.org > >>> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev >