Hi,
This kind of scares me a bit: What could session3 possibly do about this here ?
It looks like session3 is created after everything is set and done, thus it is
expected that p1==p2==-1 and thus p1-p2==0.
Regards
Felix
Am 30.11.2011 um 13:38 schrieb Michael Dürig:
>
> Hi,
>
> As documented earlier [1] new Mircokernel based JCR implementations will
> most likely introduce snapshot isolation for sessions. While I think
> this is a good thing in general, it also introduces potentially
> troublesome write skew: application level constraints might hold locally
> (i.e. per session) but might fail globally. That is, in order to enforce
> some constraints, applications might need to implement explicit cross
> session synchronization mechanisms instead of being able to rely on
> session isolation. The following test case demonstrates the issue.
>
> /**
> * Trans-session isolation differs from Jackrabbit 2.
> * Snapshot isolation can result in write skew as this
> * test demonstrates: the check method enforces an
> * application logic constraint which says that the sum
> * of the properties p1 and p2 must not be negative. While
> * session1 and session2 each enforce this constraint before
> * saving, the constraint might not hold globally as can be
> * seen in session3.
> */
> @Test
> public void testSessionIsolation() throws RepositoryException {
> Repository repository = getRepository();
>
> Session session0 = repository.login();
> Node testNode = session0.getNode("/").addNode("testNode");
> testNode.setProperty("p1", 1);
> testNode.setProperty("p2", 1);
> session0.save();
> check(getSession());
>
> Session session1 = repository.login();
> Session session2 = repository.login();
>
> session1.getNode("/testNode").setProperty("p1", -1);
> check(session1);
> session1.save();
>
> session2.getNode("/testNode").setProperty("p2", -1);
> check(session2); // Throws on JR2 but not on JR3
> session2.save();
>
> Session session3 = repository.login();
> check(session3); // Throws on JR3
> }
>
> private static void check(Session session) throws RepositoryException {
> if (session.getNode("/testNode").getProperty("p1").getLong() +
> session.getNode("/testNode").getProperty("p2").getLong() < 0) {
> fail("p1 + p2 < 0");
> }
> }
>
> Michael
>
> [1]
> http://wiki.apache.org/jackrabbit/Transactional%20model%20of%20the%20Microkernel%20based%20Jackrabbit%20prototype
