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

[Chris West]

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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