[jboss-jira] [JBoss JIRA] Commented: (JBRULES-2375) Drools hangs when events are retracted

[Paul O'Riordan (JIRA)]

    [ https://jira.jboss.org/jira/browse/JBRULES-2375?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12500589#action_12500589 ] 

Paul O'Riordan commented on JBRULES-2375:
-----------------------------------------

What appears to be happening is that:

The insert and retract methods of the NamedEntryPoint class are both synchronized via a reentrant lock  "lock". Both of these methods also require synchronized access to the actionQueue from AbstractWorkingMemory via various methods.

When the  AbstractWorkingMemory.executeQueuedActions() method (synchronized on actionQueue) is called, it executes the actions in the queue, if one of these actions is an ExpiredJob, it will trigger a retract. This method is called from fireUntilHalt (among other places) which do not synchronize on the lock in NamedEntryPoint.

The situation where deadlock occurs is as follows:

1) Insert method obtains NamedEntryPoint lock.
2) fireUntilHalt's thread obtains the lock in executeQueuedActions.
3) executeQueuedActions executes an ExpiredJob action, which calls NamedEntryPoint.retract
4) The retract method is waiting on the NamedEntryPoint lock to be released, which cannot be released 
     because the thread which is holding it is waiting for the lock on actionQueue to be released (held by
     fireUntilHalt's thread)

> Drools hangs when events are retracted
> --------------------------------------
>
>                 Key: JBRULES-2375
>                 URL: https://jira.jboss.org/jira/browse/JBRULES-2375
>             Project: Drools
>          Issue Type: Bug
>      Security Level: Public(Everyone can see) 
>          Components: drools-core (fusion)
>    Affects Versions: 5.0.1.FINAL
>         Environment: Java(TM) SE Runtime Environment (build 1.6.0_17-b04)
> Microsoft Windows XP [Version 5.1.2600]
> Intel (R) Xeon (R) CPU E5405 @ 2.00GHz (Quad Core)
>            Reporter: Paul O'Riordan
>            Assignee: Edson Tirelli
>            Priority: Blocker
>             Fix For: 5.1.0.M2
>
>         Attachments: Main.java, stacktrace.txt
>
>
> Using a StatefulKnowledgeSession (stream mode). Drools hangs when events are retracted from the session. Running the attached code results in drools hanging almost immediately. Adding the @expires property to the event declaration, e.g.
> declare Foo
>   @role (event)
>   @expires (10s)
> end
> causes drools to hang after the specified expiry time, i.e. 10 seconds.

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