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

Chris West crayzfishr at gmail.com
Tue Jul 17 13:25:10 EDT 2007 

Not quite.

It's really the opposite.  There is a change I want the engine to see now,
but my own code has not propagated the real change back around to the rule
engine just yet.  If I don't use my own proxy to hold the new value, then
other rules will fire that I don't want.  If I use my proxy, I manipulate
the value and keep the other rules from firing.  Once the "real" change
comes back around, my own proxy stops "overriding" the value and the rules
engine never even sees the real change to the underlying object.

-Chris West

On 7/17/07, Edson Tirelli <tirelli at post.com> wrote:
>
>
>    Chris,
>
>    I'm not sure I understood your scenario bellow, but it does seem
> exactly what shadow facts do: a lazy proxy.
>    In other words, lets say you have an object X. You assert X into
> working memory and the engine creates a shadow proxy for it. Then, you can
> mess with it as much as you want from outside the engine, changing its
> property values and etc... all that will be "invisible" to the engine, until
> you call an update on X. At this point, the engine will start seeing the
> current "snapshot" of the object properties...
>
>    So, my question, isn't that what you are doing with your own proxy?
>
>    []s
>    Edson
>
> 2007/7/17, Chris West <crayzfishr at gmail.com >:
> >
> > Thank you for your response to this issue.
> >
> > My use case for using proxies is this:
> >
> > The facts are not modifiable directly (no setter methods) or
> > synchronously.  Modifications to facts occur by calling another method which
> > modifies the fact and notifies the rules engine of the modification
> > asynchronously outside of the call stack (but in the same thread) that
> > triggered the change to begin with.  To give the appearance of a
> > modification until the real notification comes asynchronously, I wrap these
> > objects with proxies, and the proxy provides the ability to "override" a
> > property until the real notification comes in later in a different call
> > stack.  The reason for the modifications occurring in this fashion is driven
> > by the fact that this is a discrete event simulation, and changes to the
> > system occur only as events which are queued to execute in priority order.
> > The modifications to facts are just queued events just like everything else.
> >
> >
> > -Chris
> >
> > On 7/17/07, Edson Tirelli < tirelli at post.com> wrote:
> > >
> > >
> > >    Chris,
> > >
> > >    Unfortunately, that is true. Shadow facts exist to ensure the rules
> > > engine integrity. At this point, there is no alternative to shadow facts,
> > > because the solution we used in 3.x had too many drawbacks and did not
> > > scaled for complex rules.
> > >
> > >    We are trying to come up with an alternative strategy compatible
> > > with current architecture, but it will not make 4.0 final because we
> > > are in feature freeze for the release. It will eventually come out in a
> > > maintenance or minor release.
> > >
> > >    Can you present us your use case for asserting JDK proxies as
> > > facts?
> > >
> > >    Thanks,
> > >
> > >    []s
> > >    Edson
> > >
> > >
> > >
> > > 2007/7/17, Chris West < crayzfishr at gmail.com>:
> > > >
> > > > 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
> > > >
> > > >
> > > > _______________________________________________
> > > > rules-users mailing list
> > > > rules-users at lists.jboss.org
> > > > https://lists.jboss.org/mailman/listinfo/rules-users
> > > >
> > > >
> > >
> > >
> > > --
> > >   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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> > > https://lists.jboss.org/mailman/listinfo/rules-users
> > >
> > >
> >
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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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