[jbosscache-issues] [JBoss JIRA] Created: (JBCACHE-1543) Remove contention due to PessimisticUnversionedNode.getLock()

[Brian Stansberry (JIRA)]

Remove contention due to PessimisticUnversionedNode.getLock()
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                 Key: JBCACHE-1543
                 URL: https://jira.jboss.org/jira/browse/JBCACHE-1543
             Project: JBoss Cache
          Issue Type: Task
      Security Level: Public (Everyone can see)
          Components: Locking
            Reporter: Brian Stansberry
            Assignee: Brian Stansberry
             Fix For: 3.2.1.CR1


PessimisticUnversionedNode.getLock() shows up as a middling contention hotspot in profiling tests. The method always calls initLock(), which is a synchronized method. So any lock attempts will first have to briefly get the monitor for the node before they can move on to acquiring the lock.  This adds contention in the case of for higher level structural nodes in a tree (e.g. Fqn.ROOT).

Solution is to make the PessimisticNodeLock.lock field volatile and then only call initLock() if it is null; aka double-checked locking. Making the field volatile ensures that the IdentityLock object is fully constructed before it is visible to other threads reading PessimisticUnversionedNode.lock, which is the requirement for making double-checked locking correct.

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