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https://issues.apache.org/jira/browse/OPENJPA-2547?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14229890#comment-14229890
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Rick Curtis commented on OPENJPA-2547:
--------------------------------------
Heath --
You should use the LockLevels constant rather than a zero.
ie:
List<SQLBuffer> sqls = (sm.getLock() == null ||
sm.getLock().equals(org.apache.openjpa.kernel.LockLevels.LOCK_NONE ))
Thanks,
Rick
> When two threads attempt to get a Pessimistic Lock, one thread gets a 'false'
> lock.
> -----------------------------------------------------------------------------------
>
> Key: OPENJPA-2547
> URL: https://issues.apache.org/jira/browse/OPENJPA-2547
> Project: OpenJPA
> Issue Type: Bug
> Components: jdbc
> Affects Versions: 2.1.2, 2.2.2, 2.2.1.1, 2.3.0, 2.4.0
> Reporter: Heath Thomann
> Priority: Critical
> Attachments: OPENJPA-2547-2.1.x.patch
>
>
> I have created a scenario where two threads both attempt to get a pessimistic
> lock on an object, where one thread legitimately gets the lock, and the other
> gets a 'false' lock. To describe this issue, lets look at a test. I will
> provide (attache) a full working test, but for now lets look at this snippet
> of the test which is at the heart of the issue:
> PessimisticLockEntity entity = oem.find(PessimisticLockEntity.class, pKey);
> boolean locked = false;
> while (!locked) {
> try {
> oem.getFetchPlan().setLockTimeout(5000);
> oem.lock(entity, LockModeType.PESSIMISTIC_READ);
> locked = true;
> } catch (PessimisticLockException ple) {
> With this test, imagine the case where two threads call this code at roughly
> the same time. In this case, one thread should receive a lock, and the other
> thread should receive a PessimisticLockException (PLE). In my test, this is
> what happens.....so far so good. However, the thread with the lock (call it
> T1) then sleeps for a while, and the thread which got the PLE (call it T2)
> attempts to get the lock over and over again. When T2 tries to get a lock
> while T1 holds the lock, T2 should continue to receive a PLE. However, I've
> found that T2 "gets" a lock. That is, a PLE is never thrown because OpenJPA
> doesn't execute SQL to obtain the lock. OpenJPA skips that steps and thinks
> T2 has a lock. This gives T2 a false lock.
> I've found that prior to JIRA OPENJPA-2449, we got the expected results (i.e.
> T2 continues to get a PLE while T1 holds the lock). It is only with
> OPENJPA-2449 that the incorrect behavior occurs.
> I will provide a patch which contains a potential fix, and a test that does
> two things: 1) tests the scenario above and 2) provides a test to verify
> OPENJPA-2449 (we never provided a test when we committed OPENJPA-2449). My
> fix, if correct, simply adds one additional check to the code added via
> OPENJPA-2449.
> Thanks,
> Heath
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