[jboss-jira] [JBoss JIRA] (AS7-3343) Concurrency issues in ReferenceCountingEntityCache

[Alexey Makhmutov (JIRA)]

Alexey Makhmutov created AS7-3343:
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             Summary: Concurrency issues in ReferenceCountingEntityCache
                 Key: AS7-3343
                 URL: https://issues.jboss.org/browse/AS7-3343
             Project: Application Server 7
          Issue Type: Bug
          Components: EJB
    Affects Versions: 7.1.0.CR1b
            Reporter: Alexey Makhmutov
            Assignee: jaikiran pai
         Attachments: cacheProblemTC.zip

While running multithreaded workload against AS 7.1Beta/CR1 for application with Entity EJB 2.x we've faced a lot of following errors:
* Instance for PK [XXX] already registerd.
* Instance [YYY] not found in cache

It seems, that these errors are caused by synchronization issues in ReferenceCountingEntityCache:
* If two threads are trying to access the cache and there is no ready instance for particular PK in the cache, then both threads are trying to get some instance from the pool and put it into the cache -- as result, the second thread can get 'already registered' exception. We were able to compose a minimal test case application which reproduces this kind of problem (see below).
* There is a gap in time between the call to Associate interceptor (which puts instance in cache - via 'get' method) and Synchronization interceptor (which calls 'reference' method). During this time instance is not referenced, so it seems it can be removed by some other thread which finish its invocation at the same time. Probably this is the root cause of 'not found in cache' error, however it's hard to create a syntetic test case for it.

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