[jboss-jira] [JBoss JIRA] (WFLY-3465) Using Infinispan eviction manager can cause ConcurrentModificationException during web session access

[Paul Ferraro (JIRA)]

Paul Ferraro created WFLY-3465:
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             Summary: Using Infinispan eviction manager can cause ConcurrentModificationException during web session access
                 Key: WFLY-3465
                 URL: https://issues.jboss.org/browse/WFLY-3465
             Project: WildFly
          Issue Type: Bug
      Security Level: Public (Everyone can see)
          Components: Clustering
    Affects Versions: 8.1.0.Final
            Reporter: Paul Ferraro
            Assignee: Paul Ferraro
             Fix For: 9.0.0.Alpha1


Because wildfly stores web session using multiple cache entries, it makes liberal use of Flag.SKIP_LOCKING when locks are already held on the primary cache entry for a given session.
Infinispan's eviction manager, however, treats all cache entries the same.  Thus it may try to evict a cache entry that belongs to a session that is currently locked for use by the application - since it will have no trouble locking it - because our code assumes that all session access will first lock the primary cache entry of a session.  This manifests as a mysterious ConcurrentModificationException.

Thus, we can improve the compatibility of our code with Infinispan's eviction manager by simply removing the use of the SKIP_LOCKING flag.  Given that the only possible source of contention is the eviction manager - the cost of doing so is fairly minimal.

I should note that our default configuration does not use Infinispan eviction.  Web session passivation is instead handled by the web session clustering code.



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