Re: [hibernate-dev] JPA2 locking followup...
As I said on IRC, my belief is that we should expand this set of lock
modes specifically to include NO_WAIT variants. Its really just a
question of for which modes it makes sense. The spec says
"javax.persistence.lock.timeout" is "defined by this specification for
use in pessimistic locking" so obviously OPTIMISTIC and
OPTIMISTIC_FORCE_INCREMENT are fine by themselves.
I don't think PESSIMISTIC_FORCE_INCREMENT needs a NO_WAIT variant, even
if we were to support using this mode on non-versioned entities.
I am unclear yet whether PESSIMISTIC_READ will require a NO_WAIT
variant.
Conversely for "with wait" semantics we will need to add support for the
lock acquisition timeout.
On Fri, 2009-10-30 at 13:49 -0400, Scott Marlow wrote:
How should we handle the _NOWAIT variants for the three Pessimistic
modes? The JPA2 style is to use the "javax.persistence.lock.timeout
(time in milliseconds, with 0 meaning no wait).
Internally, we need Hibernate core to support the three pessimistic lock
modes (read, write, force_increment) with a JPA2 style timeout option.
Since, we need to support JPA2 timeout per requested lock, we might want
to support _NOWAIT via the same mechanism as we use for timeout.
On 10/30/2009 09:18 AM, Scott Marlow wrote:
> For JPA2 support, I propose that Hibernate LockMode support the
> following equivalents of JPA2 LockModeType locks:
>
>
> LockMode.OPTIMISTIC (READ)
> LockMode.OPTIMISTIC_FORCE_INCREMENT (WRITE)
> LockMode.PESSIMISTIC_READ
> LockMode.PESSIMISTIC_WRITE
> LockMode.PESSIMISTIC_FORCE_INCREMENT
>
> Hibernate already supports NONE, so that doesn't need to be added. JPA2
> defaults to LockModeType NONE.
>
> JPA1 READ + WRITE will be supported respectively via LockMode.OPTIMISTIC
> + LockMode.OPTIMISTIC_FORCE_INCREMENT.
>
> With this change, Hibernate (native (better term?)) applications would
> be able to request JPA2 like locks. This also means that JPA2
> applications running with the Hibernate Entity Manager, will see similar
> locking behavior as native applications.
>
> Pros:
>
> - Application developers will have a consistent set of locking options
> in their JPA2 based applications and native Hibernate applications.
>
> - This helps the application developer to prepare their native Hibernate
> application to migrate to JPA2.
>
> Cons:
>
> - This ties Hibernate core locking internals to the JPA2 specification.
> As JPA continues to evolve, Hibernate core should follow in lockstep.
> Although, that is not a hard requirement.
>
> - An alternative would be introducing low level locking primitives that
> could be combined to support JPA2 style locks. I can explore this path
> if there is strong push back to the above proposal.
>
> Comments?
>
> Scott
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Steve Ebersole <steve(a)hibernate.org>
Hibernate.org