[jboss-jira] [JBoss JIRA] Closed: (JBRULES-2570) KnowledgeAgent lacks a safe disposal method

[David Ward (JIRA)]

     [ https://jira.jboss.org/browse/JBRULES-2570?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

David Ward closed JBRULES-2570.
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KnowledgeAgentImpl was changed to use the new kbase.getStatefulKnowledgeSessions() method in svn revision 33962 (on trunk).

I have verified that the exposed dispose() method can now be used safely, considering users can now iterate over a kbase's stateful ksessions and dispose() them.  This will perform cleanup, remove the ksessions from the kbase, and remove the notification.  This is exactly what JBoss ESB needed.

I have also verified in a junit test - MiscTest.testGetStatefulKnowledgeSessions()  - that calling dispose() twice is safe.

> KnowledgeAgent lacks a safe disposal method
> -------------------------------------------
>
>                 Key: JBRULES-2570
>                 URL: https://jira.jboss.org/browse/JBRULES-2570
>             Project: Drools
>          Issue Type: Bug
>      Security Level: Public(Everyone can see) 
>          Components: drools-core  (expert)
>    Affects Versions: 5.1.0.M2
>            Reporter: David Ward
>            Assignee: David Ward
>            Priority: Critical
>             Fix For: 5.1.0.CR1
>
>
> In the old RuleAgent api, there were a couple methods exposed that provided a safe disposal/cleanup mechanism:
>     > ragent.stopPolling();
>     > for (StatefulSession s : ragent.getRuleBase().getStatefulSessions()) { s.dispose(); }
> In the new KnowledgeAgent api, there is only:
>     > kagent.monitorResourceChangeEvents(false);
> This is problematic for a few reasons:
>     1. Calling kagent.monitorResourceChangeEvents(false) will stop the thread that reads changesets from the queue and processes them, but the kagent will remain as a notifier listener.  So the kagent will continue putting a changeset on its queue whenever the scanner detects a change, the result of this being a memory leak.
>     2. Without a way to get at the KnowledgeBase and it's StatefulKnowledgeSessions, there is no way to cleanly dispose them.
>     3. There is currently no way for the ResourceChangeScannerService to know that it should stop "watching" a resource, because it doesn't know when there are no more listeners registered with the ResourceChangeNotifierService.  The result of this is unnecessary overhead.
> To solve #1 and #2 above, a dispose() method should be added to KnowledgeAgent that will:
>     a. Remove itself as a notifier listener.
>     b. THEN call monitorResourceChangeEvents(false) to stop it's internal thread.
>     c.  Clear it's internal queue.
>     d. Iterate over any StatefulKnowledgeSessions associated with it's KnowledgeBase, and dispose() them.
> It could be argued that #3 above should be a separate Jira issue, but it is related to this topic, so it deserves mentioning.
> Notes:
>     1. This issue is a dependency for JBoss.org ESB 4.9, which is a dependency for JBoss.com SOA-P 5.1.  The dependent Jira issue is: JBESB-3360.
>     2. This issue has been marked as Critical, although I would consider it a Blocker.  However, I will leave that decision up to the Drools team.  ;)

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