Hibernate / other ORM and pg_advisory_lock

Hi all

I'm about to settle on a database implementation for the Java part of
the development project I'm working on, and I'm wondering if anybody
here has any experience using PostgreSQL's advisory locking features
with ORM database layers like Hibernate, TopLink, OpenJPA, Cayenne,
iBatis, etc. I'm hoping to avoid relying on locking using long running
transactions that're open across user interaction (ugh) and
pg_advisory_lock etc seem well suited to the task.

At this point it's looking like I'll be using Hibernate (via Hibernate
EntityManager / JPA), so I'm especially interested in comments related
to it. In particular, in a J2SE desktop environment, has anybody here
made use (successful or otherwise) of Pg's advisory locking features?
They work fine in my test cases with Hibernate EntityManager and with
OpenJPA (not with TopLink Essentials due to connection management
issues) but working in a few reasonably simple tests is very different
from working reliably in production.

I'm particularly worried about ensuring that connections aren't cached,
pooled, or terminated & reestablished behind my back - say after an
error that results in a transaction rolling back. The connection
drop/reestablish would release any advisory locks being held, and if
that's a risk then data must be selected FOR UPDATE and compared to the
old copies before making any changes. Which also involves persuading the
ORM layer to do that, and do it the right way.

[Java newbie warning] I'm also curious about strategies people have used
to ensure reliable advisory lock release when the persistence layer
finishes with the object. I'd prefer to avoid the need to explicitly
release the locks, instead having them released when the persistence
layer "forgets" about the object. In C++ (w/o a gc at least) I might
just use a dtor, but with the unpredictability of destruction timing in
a gc'd environment it's not so attractive in Java. Right now I'm
inclined to define a finish() method that causes all subsequent calls to
accessors to throw, and call it from finalize in case some code path
fails to call it manually when done with the object. Totally stupid, or
workable sounding? [/Java newbie warning]

So ... any thoughts/experiences using Hibernate or other ORM tools with
Pg's advisory locking?

--
Craig Ringer