[jboss-jira] [JBoss JIRA] Commented: (JBRULES-2756) fireUntilHalt is doing busy wait and consuming 100% of one CPU core

[Greg Barton (JIRA)]

    [ https://jira.jboss.org/browse/JBRULES-2756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12559579#action_12559579 ] 

Greg Barton commented on JBRULES-2756:
--------------------------------------

Yep. :)

> fireUntilHalt is doing busy wait and consuming 100% of one CPU core
> -------------------------------------------------------------------
>
>                 Key: JBRULES-2756
>                 URL: https://jira.jboss.org/browse/JBRULES-2756
>             Project: Drools
>          Issue Type: Bug
>      Security Level: Public(Everyone can see) 
>          Components: drools-core
>    Affects Versions: 5.1.0.FINAL, 5.1.1.FINAL
>            Reporter: Edson Tirelli
>            Assignee: Edson Tirelli
>             Fix For: 5.2.0.M1
>
>
> Analysis by Greg Barton:
> =========================
> The problem is the race condition fix introduced in rev 30163.  The missedNotifyAll flag is set to true immediately which causes the busy loop.
> missedNotifyAll is initialized to false, but is immediately set to true because notifyHalt() is called in AbstractWorkingMemory.queueWorkingMemoryAction() via ReteooRuleBase.newStatefulSession().  Anyway, I'll move discussions of possible solutions over to the dev list, (crossposting now) or a JIRA if you'd prefer that.
> Here's a diff for the minimal change I think fixes the problem:
> Index: src/main/java/org/drools/common/DefaultAgenda.java
> ===================================================================
> --- src/main/java/org/drools/common/DefaultAgenda.java  (revision 35727)
> +++ src/main/java/org/drools/common/DefaultAgenda.java  (working copy)
> @@ -1048,10 +1048,10 @@
>             boolean fired = fireNextItem( agendaFilter );
>             fired = fired || !((AbstractWorkingMemory) this.workingMemory).getActionQueue().isEmpty();
>             this.workingMemory.executeQueuedActions();
> -            if ( !fired && !missedNotifyAll.get()) {
> +            if ( !fired ) {
>                 try {
>                     synchronized ( this.halt ) {
> -                        this.halt.wait();
> +                        if(!missedNotifyAll.get()) this.halt.wait();
>                     }
>                 } catch ( InterruptedException e ) {
>                     this.halt.set( true );
> Basically, move the missedNotifyAll check immediately before the wait.  This still avoids the race condition, and only causes one spurious trip through the fireUntilHalt loop on startup.  I'd open a JIRA with this in it but I need to get to sleep. :)

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