[jboss-jira] [JBoss JIRA] (WFLY-2521) EJB backing cache's can generate large retention from cancelled tasks in its scheduled executor's DelayedWorkQueue

[Aaron Ogburn (JIRA)]

Aaron Ogburn created WFLY-2521:
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             Summary: EJB backing cache's can generate large retention from cancelled tasks in its scheduled executor's DelayedWorkQueue
                 Key: WFLY-2521
                 URL: https://issues.jboss.org/browse/WFLY-2521
             Project: WildFly
          Issue Type: Bug
      Security Level: Public (Everyone can see)
          Components: EJB
    Affects Versions: 8.0.0.Beta1
            Reporter: Aaron Ogburn
            Assignee: David Lloyd


EJB backing cache's frequently cancel remove and passivation tasks with each access and replace them with new ones.  Per http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ScheduledThreadPoolExecutor.html cancelled tasks are not removed from queue until their scheduled delay passes.

So due to the java ScheduledThreadPoolExecutor's lazy cancelled task removal, this scheduled task cancellation and recreation model can potentially churn up quite a number of queued cancelled tasks sitting in the executor's DelayedWorkQueue.  With longer timeouts and frequent ejb access, this can generate substantial heap overhead.

It should be pretty easy to help limit any such build up by calling purge() [1] on the scheduled executor.  Likely don't want to purge with each cancel, so perhaps a purge() could be called on a configurable time delay or after a configurable amount of cancels?

[1] http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/ThreadPoolExecutor.html#purge%28%29

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