[Hibernate] What would a good locking API look like?

[Gavin K. <ga...@ap...>]

Hi, I've been thinking about improving Hibernate's locking API recently.
Currently your object could be in 3 different states:

* No lock, for example if you just called session.update(foo) or if the
session was disconnected
* Shared lock, for example if you just called session.load(id) or
session.find(query)
* Exclusive lock, if you called session.loadWithLock(id) or
session.lock(foo), or if changes to the object have been flush()ed

There is currently no mechanism for upgrading a lock from No lock to Shared
lock, ie. to do a version check for an object.

So I'm wondering about deprecating Session.lock() and Session.loadWithLock()
and replacing them with

Session.load(clazz, id, lockMode)
Session.load(object, id, lockMode)
Session.lock(object, lockMode)

I would introduce a new class,

public class LockMode {
  public static final LockMode NONE;
  public static final LockMode SHARED;
  public static final LockMode EXCLUSIVE;
}

Then

Session.loadWithLock(clazz, id) == Session.load(clazz, id,
LockMode.EXCLUSIVE)
Session.lock(foo) == Session.lock(foo, LockMode.EXCLUSIVE)

There is also a certain argument for allowing Session.update(foo, lockMode),
but thats a bit more difficult to implement, so lets leave it for later....

Ideas + criticisms are very welcome!

Gavin