[hibernate-dev] Bytecode enhanced, Reference Cached immutable Entities
John O'Hara
johara at redhat.com
Fri Mar 27 07:04:16 EDT 2015
On 26/03/15 16:22, Steve Ebersole wrote:
> The contract I suggested btw is missing one use case I know we have
> discussed in regards to OGM a few times... the ability to store
> references to datastore specific locators (I think the use case was to
> efficiently load collections through that datastore reference). But
> that (obviously) requires passing extra, specific state into
> the createEntityEntry method. Not really sure the best way to handle
> such things tbh.
>
If we did have a "creation Context" parameter passed to the
createEntityEntry, we would be instantiating more objects, however if we
went with Sanne' suggestion if caching the EnityEntryFactory with the
EntityPersister, how many objects would be actually created? I am not
sure about the relationship between Entity, EntityEntry and Session but
could this a possibility if there is a 1-1 relationship between
EntityPersister and no. of different Entities definitions?
> On Thu, Mar 26, 2015 at 11:16 AM, Steve Ebersole <steve at hibernate.org
> <mailto:steve at hibernate.org>> wrote:
>
> Apparently I hit some key combo that means send :) To finish up...
>
> On Thu, Mar 26, 2015 at 10:58 AM, Steve Ebersole
> <steve at hibernate.org <mailto:steve at hibernate.org>> wrote:
>
>
> On Thu, Mar 26, 2015 at 10:20 AM, Sanne Grinovero
> <sanne at hibernate.org <mailto:sanne at hibernate.org>> wrote:
>
>
> Concurrency
> Since the goal is to share the ImmutableEntityEntry
> instance among
> multiple threads reading it, I'd rather make sure that it
> is really
> immutable. For example it now holds onto potentially lazy
> initialized
> fields, such as getEntityKey().
> If it's not possible to make it really immutable (all
> final fields),
> we'll need to make it threadsafe and question the name I'm
> proposing.
>
>
> The specific use-case John is interested in does indeed need
> to be completely thread-safe and fully concurrent.
>
>
> LockMode
> From a logical perspective of users, one might think
> that an entity
> being "immutable" doesn't necessarily imply I can't lock
> on it..
> right? I'm not sure how far it could be a valid use case,
> but these
> patches are implying that one can't lock an immutable
> entity anymore,
> as the lock state would be as immutable as anything else
> on the
> EntityEntry.
> Are we good with that? Alternatively one might need to
> think to
> separate the lock state handling from the EntityEntry.
>
>
> Conceptually there is nothing wrong with requesting a READ
> lock on an immutable entity. But like you said, what is the
> logical expectation there? IMO there should be none. But if
> we decide that it is OK to req
>
> But if we decide that it is OK to request a lock on an immutable
> entity, that is problematic for the idea of a "SharedEntityEntry"
> or an "ImmutableEntityEntry" because a lock is associated with a
> Session which is what the EntityEntry is meant to model... an
> entity's information in relation to a Session. Aka, it now needs
> to hold state.
>
>
>
> Notice I said immutable here and not READ_ONLY which is a
> specific distinction which is important to other parts of your
> email that I will address in a second email.
>
>
> On smaller details:
> # org.hibernate.engine.internal.SharedEntityEntry is
> hosted in an
> .internal package, I don't think it's right to refactor
> all the public
> API javadoc which was referring to EntityEntry to now
> refer to the
> internal implementation.
> # things like EntityEntryExtraState should probably get
> moved to
> .internal packages as well now - we couldn't do that
> before without
> breaking either encapsulation or APIs.
>
>
> +1
>
>
> In terms of git patches, the complexity of the changeset
> risks to get
> a bit our of hand. What about we focus on creating a clean
> pull
> request which focuses exclusively on making EntityEntry an
> interface,
> and move things to the right packages and javadoc?
>
>
> Agree 100%
>
> You'd have a trivial EntitEntryFactory, and we can then
> build the
> evolution on top of that, not least maybe helping out by
> challenging
> some points in parallel work.
> These are the things I'd leave for a second iteration:
> - add various implementations of EntityEntry iteratively,
> as needed
> - the strategy such a Factory would use the pick an
> implementation
> - ultimately, make it possible for an integrator to
> override such a Factory
>
>
> This all seems reasonable. For 5.0 I think the most important
> thing is to nail down the idea of EntityEntry as an interface,
> introduce a Factory for building them and agree on the signature
> for building them. Granted we may need iteration to finalize the
> actual Factory signature, especially as OGM finally starts to use
> it, but I think that in general we can get it pretty close. Worst
> case we just pass high-level constructs like the EntityPersister
> (which OGM supplies custom impls) and the Session and all the
> "EntityEntry state". For the purpose of starting a discussion:
>
> public interface EntityEntryFactory {
> public EntityEntry createEntityEntry(
> PersistenceContext persistenceContext,
> EntityPersister persister,
> Status status,
> Serializable id,
> Object version,
> Object[] loadedState,
> Object rowId,
> LockMode lockMode,
> boolean existsInDatabase,
> boolean disableVersionIncrement,
> boolean lazyPropertiesAreUnfetched);
> }
>
> I would suggest a "creation context" method param object to pass
> in here, but seeing as how we are trying to stop instantiations...
>
> I would prefer the definition of the EntityEntryFactory to use be
> defined via SessionFactoryBuilder interface. I already have plans
> to have a auto-loaded hook for integrators to be able to adjust
> the SessionFactoryBuilder. But as a Service is fine too.
>
>
> For example with Hibernate OGM we might want to override / re
> configure the factories to use custom EntityEntry
> implementations -
> requirements are not fully clear at this point but it
> seems likely.
>
> The priority being to define the API as that would be a
> blocker for
> 5.0, we have then better choices to leave more smarter and
> advanced
> EntityEntry implementations for the future; we'd still need to
> implement at least the essential ones to make sure the API
> of the
> EntityEntryFactory has all the context it needs.
>
> Thanks,
> Sanne
>
>
> On 24 March 2015 at 09:27, John O'Hara <johara at redhat.com
> <mailto:johara at redhat.com>> wrote:
> > Steve,
> >
> > Have you had chance to look at this? Do you have any
> comments/observations?
> >
> > Thanks
> >
> > John
> >
> >
> > On 17/03/15 09:24, John O'Hara wrote:
> >
> > Steve,
> >
> > I have been having a think about the EntityEntry
> interface, and have forked
> > a branch here:
> >
> >
> https://github.com/johnaoahra80/hibernate-orm/tree/EntityEntryInterface
> >
> > I know it is nowhere near complete, but was this the
> sort of idea you had in
> > mind?
> >
> > Thanks
> >
> > John
> >
> >
> > On 13/03/15 09:44, John O'Hara wrote:
> >
> > EntityEntry retains a reference to a persistenceContext
> internally that
> > org.hibernate.engine.spi.EntityEntry#setReadOnly makes
> calls to, is this
> > where the session reference is kept? As
> > org.hibernate.engine.spi.PersistenceConext is an
> interface could we have a
> > different implementation for this use case? e.g. an
> > ImmutablePersistenceContext that could be shared across
> sessions?
> >
> > For the bytecode enhancement, could we change the
> enhancer so that it adds
> > an EntityEntry interface with javassist.
> > ClassPool.javassist.ClassPool.makeInterface()() as
> opposed to adding a class
> > javassist.ClassPool.makeClass()? I need to have a look
> at javassit to
> > confirm what javassist.ClassPool.makeInterface() does.
> >
> > Thanks
> >
> > John
> >
> > On 12/03/15 18:52, Steve Ebersole wrote:
> >
> > It is possible. Although some of the changes are
> particularly painful.
> > Most of EntityEntry, if it is an interface, can be made
> to work with your
> > use case.
> org.hibernate.engine.spi.EntityEntry#setReadOnly I think
> is the
> > one exception, because:
> > 1) your use case needs it
> > 2) it expects the Session to be available internally
> (its not passed)
> >
> > The bigger thing I am worried about for you is the
> bytecode stuff, as that
> > ties very tightly with EntityEntry.
> >
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--
John O'Hara
johara at redhat.com
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