[rules-users] The effect of not using shadow facts
Chris West
crayzfishr at gmail.com
Wed Jul 18 10:27:47 EDT 2007
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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> --
> 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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