I am a bit confused as to how hibernate implements pessismistic locking for the EntityManager?

I have a written a simple tests which spawns two threads, the first thread calls EntityManager.lock(theEntity, LockModeType.WRITE);

The second thread seems to hand indefinetly when it accesses the same entity, even when the first thread has finished and closes the entity manager it uses?

I also notice that the JPA does not specify how pessimistic locking should be implemented it leaves it up to the vendor.

So what does hibernate do?

select ... for update so your DB might hang on