Mark Little commented on JBTM-1350:
Code commented out in 2PC methods ...
// ThreadActionData.pushAction(theTransaction); // unnecessary if context goes with all
... can be uncommented for LockManager. I'm unsure when it was commented out, but it
was a long time ago and presumably when we were doing less with LockManager or just being
lucky enough not to run into these cc issues.
Deadlock in LockManager
Project: JBoss Transaction Manager
Issue Type: Bug
Security Level: Public(Everyone can see)
Components: Transaction Core
Affects Versions: 5.0.0.M1, 4.17.2
Reporter: Michael Musgrove
Assignee: Michael Musgrove
Fix For: 5.0.0.M3
Attachments: deadlock_via_intrinsic_lock, deadlock_via_ServerNestedAction,
Original Estimate: 1 day
Remaining Estimate: 1 day
A deadlock can occur whilst calling LockManager.setlock if another thread tries to commit
a transaction that has the same lock manager as a participant. The attached java stack
dump, jstack.16785, (from test com.hp.mwtests.ts.jts.remote.hammer.DistributedHammer2)
shows an example. It shows two threads interacting with a remote HammerObject:
- Thread 1 updates the remote object;
- Thread 2 commits a transaction that has the same HammerObject instance as a
Thread 1 calls setlock on HammerObject which synchronizes on BasicAction.Current() and
LockManager.locksHeldLockObject and then activates the object (which triggers an object
load from the object store). The activate call tries to lock StateManager.mutex and this
is where thread 1 deadlocks.
Meanwhile a commit request is issued which results in Thread 2 running at the same time
thread 1 is calling activate. The commit asks HammerObject to prepare and commit. The
participant commit asks HammerObject to release any locks it has held
(LockManager.releaseAll). This call first tries to lock BasicAction.Current() which is
null during commit time (since commit disassociates the transaction from the thread before
committing the participants). Instead it locks StateManager.mutex which succeeds. Then it
tries to lock LockManager.locksHeldLockObject and that is where Thread 2 deadlocks.
Note that the problem arises because Thread 2 gets null when it calls
BasicAction.Current() and instead locks StateManager.mutex. If BasicAction.Current() was
not null thread 2 would try to lock it but would not obtain the lock until thread 1 had
completed the activate call and released BasicAction.Current() thus allowing thread 2 to
continue as normal.
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