[rules-users] The effect of not using shadow facts

Chris West crayzfishr at gmail.com
Wed Jul 18 12:38:42 EDT 2007 

Edson,

It is certainly possible to create a JDK proxy with only some of the
interfaces that are present on the delegate object that you are proxying,
but in my case, my proxies have all the interfaces of the underlying object.

The top two lines of the call stack I sent shows the following:

Exception in thread "main" java.lang.ClassCastException:
ascc.status.FlightOpsStatusBoard$LaunchRecoveryStatusShadowProxy
    at
org.drools.base.ascc.status.AirPlanStatusBoard$SortieStatus$getState.getValue(Unknown
Source)

What's strange here is that the ClassCastException seems to be caused by
casting an object of type SortieStatus to type
LaunchRecoveryStatusShadowProxy, if I'm reading that right.  The types
SortieStatus and LaunchRecoveryStatus are both interfaces in my code, and
they never appear on the same fact object (so no SortieStatus will ever be a
LaunchRecoveryStatus and vice-versa).  So I'm wondering why the cast is
occuring, since it is not possible to work.

The unfortunate part is I cannot see into the class where the cast is
occurring, as it is a generated class created by drools.

-Chris West

On 7/18/07, Edson Tirelli <tirelli at post.com> wrote:
>
>
>    Chris,
>
>     For the solution to work, it is important that a superclass or
> interface matches all the ObjectTypes in your rulebase that your final class
> (proxy) matches... I guess that is the case with JDK proxies, isn't it?
>
>     []s
>     Edson
>
> 2007/7/18, Chris West <crayzfishr at gmail.com>:
> >
> > Edson,
> >
> > I downloaded and built the latest from the trunk of the repository.  I
> > applied this new build toward my test case, and it seemed to fix the
> > problem.  However, when I applied it to my real project, it still exhibits
> > the problem.  If I discover more information about the problem I'll let you
> > know.
> >
> > Thanks,
> > Chris West
> >
> > On 7/17/07, Edson Tirelli < tirelli at post.com> wrote:
> > >
> > >
> > >    Chris,
> > >
> > >    I found and developed an intermediate solution that shall work for
> > > your proxies.
> > >    If it is not possible to create a shadow fact for a class that is
> > > asserted (because the class is final or whatever), the engine goes up in the
> > > class hierarchy, looking for a class or interface for which is possible to
> > > create the proxy, but that still matches all ObjectTypes available in the
> > > rule base matched by the original class. The analysis is a bit complex,
> > > specially because new rules with new object types can be dynamically added
> > > to the rule base, but I believe the solution will work for JDK proxies and
> > > the most common proxy frameworks out there, that usually don't proxy
> > > multiple unrelated interfaces at once.
> > >
> > >    So, I ask you please to get latest snapshot from the repository and
> > > try it out for your use case and report back to the list the results, since
> > > seems there are a few other people using similar things.
> > >
> > >     Thanks,
> > >         Edson
> > >
> > >
> > > 2007/7/17, Chris West < crayzfishr at gmail.com>:
> > > >
> > > > Is that still true if the equals() and hashcode() methods are only
> > > > based on the identity fields of the object (which cannot change)?
> > > >
> > > > -Chris West
> > > >
> > > > On 7/17/07, Mark Proctor <mproctor at codehaus.org> wrote:
> > > > >
> > > > >  you only need to use modifyRetract if the object is inserted. The
> > > > > reason for this is if you change field values on your facts we will not be
> > > > > able to remove them from our various internal hashmaps; thus the need to
> > > > > remove first prior to any changes, then make the changes and then insert it
> > > > > again. We can't allow users to just call update() as we have no idea what
> > > > > the old values where, thus we cannot find the objects in our hashmaps.
> > > > >
> > > > > Mark
> > > > > Chris West wrote:
> > > > >
> > > > > Mark,
> > > > >
> > > > > Using modifyRetract and modifyInsert seems to fix the problem (at
> > > > > least in my test case I finally created).  I'll try this on my real code.
> > > > >
> > > > > My only concern here is that it puts the burden on the rule author
> > > > > to know whether things are being shadowed or not.  For shadowing that is
> > > > > explicitly turned off this is ok.  But for implicit non-shadowing based on a
> > > > > class being final, this is not at all obvious to the rule auther.
> > > > >
> > > > > Is there any way to have this hidden such that I can still call
> > > > > "update" but have it use "modifyRetract" and "modifyInsert" instead?
> > > > >
> > > > > Also, I'm curious why I have to call modifyRetract before I start
> > > > > modifing the object, since the engine does not know about my modifications
> > > > > anyway until I call update or modifyInsert?  By the way, I was unable to use
> > > > > the block setter approach in the rule consequence due to not having set
> > > > > methods for modifying my objects.
> > > > >
> > > > > Thanks,
> > > > > -Chris West
> > > > >
> > > > > On 7/17/07, Mark Proctor <mproctor at codehaus.org > wrote:
> > > > > >
> > > > > > If you do not have shadow facts you cannot use the update()
> > > > > > method, it will leave the working memory corrupted. Instead you must manage
> > > > > > this yourself, before you change any values on the object you must call
> > > > > > modifyRetract() and after you hvae finished your changes ot hte object call
> > > > > > modifyInsert() - luckily if you are doing this in the consequence you can
> > > > > > use the MVEL modify keyword combined with the block setter and it does this
> > > > > > for you:
> > > > > > modify ( person ) { age += 1, location = "london" }
> > > > > >
> > > > > > Mark
> > > > > > Chris West wrote:
> > > > > >
> > > > > > Hello,
> > > > > >
> > > > > > With prior versions of JBoss Rules (3.0.5) I have been using JDK
> > > > > > generated dynamic proxies as facts, and they have been working fine.
> > > > > > However, after upgrading to JBoss Rules 4.0.0MR3, I cannot seem
> > > > > > to get the dynamic proxies to work as facts.  It seems that even though a
> > > > > > rule fires that changes a field on the proxy, a second rule that should not
> > > > > > be activated after the update still fires.
> > > > > >
> > > > > > According to the JDK javadoc documentation, dynamic proxies are
> > > > > > created as final.  My assumption is that JBoss Rules is not creating Shadow
> > > > > > facts for these since they are final.  After reading the JIRA at
> > > > > > http://jira.jboss.com/jira/browse/JBRULES-960, I now am
> > > > > > questioning what the effect of not using shadow facts is on the engine.  The
> > > > > > relevant part of that is:
> > > > > >
> > > > > > "The problem is that SpringAOP is generating a proxy whose
> > > > > > methods equals() and hashCode() are "final". As drools must either override
> > > > > > these methods in the shadow proxy or not shadow the fact at all, I'm
> > > > > > disabling shadow proxy generation for this use case.
> > > > > > It is really important to note that if you are asserting
> > > > > > SpringAOP proxies as facts into the working memory, you will not be able to
> > > > > > change any field value whose field is constrained in rules or you may incur
> > > > > > in a memory leak and non-deterministic behavior by the rules engine.
> > > > > > Unfortunately there is nothing we can do about, since when SpringAOP makes
> > > > > > the methods equals and hashcode final, we can't override them anymore and as
> > > > > > so, we can't shadow them."
> > > > > >   [ Show » <http://jira.jboss.com/jira/browse/JBRULES-960> ]
> > > > > >   Edson Tirelli<http://jira.jboss.com/jira/secure/ViewProfile.jspa?name=tirelli>
> > > > > > [02/Jul/07 03:29 PM] The problem is that SpringAOP is generating
> > > > > > a proxy whose methods equals() and hashCode() are "final". As drools must
> > > > > > either override these methods in the shadow proxy or not shadow the fact at
> > > > > > all, I'm disabling shadow proxy generation for this use case. It is really
> > > > > > important to note that if you are asserting SpringAOP proxies as facts into
> > > > > > the working memory, you will not be able to change any field value whose
> > > > > > field is constrained in rules or you may incur in a memory leak and
> > > > > > non-deterministic behavior by the rules engine. Unfortunately there is
> > > > > > nothing we can do about, since when SpringAOP makes the methods equals and
> > > > > > hashcode final, we can't override them anymore and as so, we can't shadow
> > > > > > them.
> > > > > >
> > > > > > Although I'm not using SpringAOP, I believe my facts are not
> > > > > > being shadowed.
> > > > > >
> > > > > > Is it true that not using shadow facts may lead to
> > > > > > non-deterministic behavior?  Prior to shadow facts, the engine seemed to
> > > > > > handle it.  Any chance of reverting back to the old style of truth
> > > > > > maintenance in the case of not using shadow facts.
> > > > > >
> > > > > > I apologize if I'm not on the right track here.  My only test
> > > > > > case for my problem is the entire application right now, so I cannot offer
> > > > > > it for discussion.  Any advice would be greatly appreciated.
> > > > > >
> > > > > > Thanks,
> > > > > > -Chris West
> > > > > >
> > > > > >  ------------------------------
> > > > > >
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> > > > > >
> > > > > >
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> > > > > >
> > > > > >
> > > > > >
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> > >
> > > --
> > >   Edson Tirelli
> > >   Software Engineer - JBoss Rules Core Developer
> > >   Office: +55 11 3529-6000
> > >   Mobile: +55 11 9287-5646
> > >   JBoss, a division of Red Hat @ www.jboss.com
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> --
>   Edson Tirelli
>   Software Engineer - JBoss Rules Core Developer
>   Office: +55 11 3529-6000
>   Mobile: +55 11 9287-5646
>   JBoss, a division of Red Hat @ www.jboss.com
>
> _______________________________________________
> rules-users mailing list
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