11:30 a.m.
Godmar,
Shadow Facts are a necessary evil in current version. Basically what they
do is keep the working memory consistent in face of attribute changes on the
facts, that may happen both internally and externally to the working memory.
Our implementation to shadow facts is a lazy proxy that caches the values
until a safe point to synchronize the actual attribute value with the one
seen by the engine.
So, the question is: given an object:
(Map) fact
How can we create an identical copy of it (shadow), if there is no
"clone" operation? More than that, the shadow must be a subclass of it.
Most Collection and Map implementations have a single parameter
constructor that allows us to do:
proxy = (ShadowProxy) this.shadowClass.getConstructor( new Class[]{cls}
).newInstance( new Object[]{fact} );
But the SingletonMap you were using does not accept that constructor.
So, one way is to explicit check if the fact is a SingletonMap and handle it
accordingly, but that is a specific class hack... is there any general
solution we can use?
[]s
Edson
2008/2/20, Godmar Back <godmar(a)gmail.com>:
I don't really understand what you mean by "shadow". What is the
purpose of such shadowing. Mark's email implies that it has to do with
concurrency protection; it's not clear what that means.
In my view, whatever purpose you pursue with "shadowing", it does not
justify treating beans and maps differently.
Your example of class Person shows that. If a person has two
attributes, name and age, then this is equivalent to a map with two
keys 'name' and 'age'.
Here's the mapping:
p.getName() corresponds to m["name"]
p.getAge() corresponds to m["age"]
and setName/setAge accordingly.
Mathematically, a bean is an associative array with a fixed set of
keys (called "properties") that map to values. For all practical
purposes, that is the same as a map. There's no reason to treat them
differently. Wherever you'd do "getXXX()" with a bean you'd do
.get("XXX") with a map.
- Godmar
On Feb 20, 2008 11:25 AM, Edson Tirelli <tirelli(a)post.com> wrote:
>
> Ok, let me show one example. Imagine the class Person, with 2
attributes
> (name and age) and the corresponding getter/setters.
> What are the data for that fact that must be shadowed? easy answer:
just
> shadow all getXXX() methods (getName and getAge).
>
> Now, take a Map. What is the data that must be shadowed?
>
> So, we do our best to work with facts that don't follow the javabean
> spec, but collections and maps are a complicated beast. Again, if you
have
> suggestions on how to improve the current support we provide for them,
> please share with us.
>
> []s
> Edson
>
> 2008/2/20, Godmar Back <godmar(a)gmail.com>:
>
> > On Feb 20, 2008 9:23 AM, Edson Tirelli <tirelli(a)post.com> wrote:
> > >
> > > Godmar,
> > >
> > > Short answer: collection/maps objects are not javabeans.
> > >
> >
> > Explain why this is a problem.
> >
> > What is it about JavaBeans that your algorithm relies upon? Is it the
> > fact that the set of properties remains fixed and can be determined at
> > (fact) insertion time via reflection?
> >
> > Otherwise, I do not see any conceptual difference between a map and a
> bean.
> > If that is the difference, then please allow maps with an immutable
key
> set.
> >
> > - Godmar
> >
> >
> > > Long answer: collection/maps must be shadowed to ensure
consistency
> > > during execution, but how can we shadow the data if it is not
exposed in
> a
> > > default, spec manner, as in javabeans? The algorithm we have in
place
> right
> > > now is bellow. As you can see, it is a weak algo, but was the best I
> could
> > > come up at that time. If you have any suggestions on how to improve
> that, I
> > > appreciate.
> > >
> > > public Object getShadow(final Object fact) throws
> RuntimeDroolsException
> > > {
> > > ShadowProxy proxy = null;
> > > if ( isShadowEnabled() ) {
> > > try {
> > > if ( Collection.class.isAssignableFrom(
this.shadowClass
> )
> > > || Map.class.isAssignableFrom( this.shadowClass ) ) {
> > > // if it is a collection, try to instantiate
using
> > > constructor
> > > try {
> > > proxy = (ShadowProxy)
> > > this.shadowClass.getConstructor( new Class[]{cls} ).newInstance( new
> > > Object[]{fact} );
> > > } catch ( Exception e ) {
> > > // not possible to instantiate using
constructor
> > > }
> > > }
> > > if ( proxy == null ) {
> > > if ( this.instantiator == null ) {
> > > this.setInstantiator();
> > > }
> > > proxy = (ShadowProxy)
> this.instantiator.newInstance();
> > > }
> > >
> > > proxy.setShadowedObject( fact );
> > > } catch ( final Exception e ) {
> > > System.out.println( "shadow: " +proxy.getClass()
+
":" +
> > > fact.getClass() );
> > > throw new RuntimeDroolsException( "Error creating
shadow
> > > fact for object: " + fact,
> > > e );
> > > }
> > > }
> > > return proxy;
> > >
> > >
> > > }
> > >
> > > []s
> > > Edson
> > >
> > > 2008/2/19, Godmar Back <godmar(a)gmail.com>:
> > > > As a general comment, the examples for which I find Drools failing
are
> > > > not the actual examples for which my application is failing.
It's
just
> > > > the smallest test case I was able to eliminate.
> > > >
> > > > I'm now a bit concerned about your comment that Maps and
Collections
> > > > aren't well-defined as Facts. I am planning to make extensive
use
of
> > > > them (that's also why I'd prefer to use the MVEL dialect,
because
in
> > > > Java I cannot do this without creating Bean wrappers.)
> > > >
> > > > Could you elaborate what makes the semantics not
"well-defined".
> > > >
> > > > I'm specifically concerned with immutable maps (such as the one
that
> > > > would have been returned by Collections.singletonMap), and with
> > > > collections of maps (such as those obtained via a
"from"..."
clause).
> > > > I need to insert immutable maps as facts; I understand that the
items
> > > > returned by "from" aren't inserted as facts.
> > > >
> > > > - Godmar
> > > >
> > > > On Feb 19, 2008 3:11 PM, Edson Tirelli <tirelli(a)post.com>
wrote:
> > > > >
> > > > > Drools tries to create the ShadowProxy. The reason is that
it
> does
> > > not
> > > > > know about the implementation... it just knows it is a Map and
as
> so, it
> > > > > must be shadowed. Problem is that SingletonMap is either final
or
> does
> > > not
> > > > > have a default constructor.
> > > > > My recommendation, besides opening a JIRA for this, is
avoid
> > > inserting
> > > > > collections/maps directly as facts. The semantic for such facts
is
> not
> > > > > clearly defined and it may cause undesired behavior.
> > > > >
> > > > > []s
> > > > > Edson
> > > > >
> > > > > 2008/2/19, Godmar Back <godmar(a)gmail.com>:
> > > > > >
> > > > > >
> > > > > >
> > > > > > Hi,
> > > > > >
> > > > > > usings Drools 4.0.4 and MVEL 1.4, this simple rule:
> > > > > > ---
> > > > > > package test;
> > > > > >
> > > > > > import java.util.Collections;
> > > > > >
> > > > > > dialect "mvel"
> > > > > >
> > > > > > rule "Rule #1"
> > > > > > when
> > > > > > then
> > > > > > insert(Collections.singletonMap("content",
"hello"));
> > > > > > end
> > > > > > --
> > > > > >
> > > > > > produces:
> > > > > > java.lang.IllegalAccessError: class
> > > > > >
org.drools.shadow.java.util.Collections$SingletonMapShadowProxy
> cannot
> > > > > > access its superclass java.util.Collections$SingletonMap
> > > > > > at java.lang.ClassLoader.defineClass1(Native
Method)
> > > > > > at
java.lang.ClassLoader.defineClass(ClassLoader.java
:620)
> > > > > > at
> > > > >
> > >
> org.drools.rule.MapBackedClassLoader.fastFindClass(
MapBackedClassLoader.java:60)
> > > > > > at
> > > > >
> > >
> org.drools.rule.MapBackedClassLoader.loadClass(MapBackedClassLoader.java
:79)
> > > > > > at
java.lang.ClassLoader.loadClass(ClassLoader.java
:251)
> > > > > > at
> > > > >
> > >
> org.drools.reteoo.Rete$ClassObjectTypeConf.loadOrGenerateProxy(Rete.java
:547)
> > > > > > at
> > > > >
> > >
> org.drools.reteoo.Rete$ClassObjectTypeConf.defineShadowProxyData(
Rete.java:494)
> > > > > > at
> > > > >
org.drools.reteoo.Rete$ClassObjectTypeConf.<init>(Rete.java:461)
> > > > > > at
org.drools.reteoo.Rete.assertObject(Rete.java:152)
> > > > > > at
> > > > >
> org.drools.reteoo.ReteooRuleBase.assertObject(ReteooRuleBase.java:192)
> > > > > > at
> > > > >
> > >
> org.drools.reteoo.ReteooWorkingMemory.doInsert(ReteooWorkingMemory.java
:71)
> > > > > > at
> > > > >
> > >
> org.drools.common.AbstractWorkingMemory.insert(
AbstractWorkingMemory.java:909)
> > > > > > at
> > > > >
> > >
> org.drools.common.AbstractWorkingMemory.insert(
AbstractWorkingMemory.java:881)
> > > > > > at
> > > > >
> > >
> org.drools.base.DefaultKnowledgeHelper.insert(
DefaultKnowledgeHelper.java:67)
> > > > > > at
> > > > >
> > >
> org.drools.base.DefaultKnowledgeHelper.insert(
DefaultKnowledgeHelper.java:61)
> > > > > >
> > > > > >
> > > > > > It's not clear to me why Drools creates Proxies for
such
classes
> as
> > > > > > java.util.Collections, or does MVEL do it?
> > > > > >
> > > > > > - Godmar
> > > > > > _______________________________________________
> > > > > > rules-users mailing list
> > > > > > rules-users(a)lists.jboss.org
> > > > > > https://lists.jboss.org/mailman/listinfo/rules-users
> > > > > >
> > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Edson Tirelli
> > > > > JBoss Drools Core Development
> > > > > Office: +55 11 3529-6000
> > > > > Mobile: +55 11 9287-5646
> > > > > JBoss, a division of Red Hat @ www.jboss.com
> > > > > _______________________________________________
> > > > > rules-users mailing list
> > > > > rules-users(a)lists.jboss.org
> > > > > https://lists.jboss.org/mailman/listinfo/rules-users
> > > > >
> > > > >
> > > > _______________________________________________
> > > > rules-users mailing list
> > > > rules-users(a)lists.jboss.org
> > > > https://lists.jboss.org/mailman/listinfo/rules-users
> > > >
> > >
> > >
> > >
> > > --
> > > Edson Tirelli
> > > JBoss Drools Core Development
> > > Office: +55 11 3529-6000
> > > Mobile: +55 11 9287-5646
> > > JBoss, a division of Red Hat @ www.jboss.com
> > > _______________________________________________
> > > rules-users mailing list
> > > rules-users(a)lists.jboss.org
> > > https://lists.jboss.org/mailman/listinfo/rules-users
> > >
> > >
> > _______________________________________________
> > rules-users mailing list
> > rules-users(a)lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/rules-users
> >
>
>
>
>
> --
> Edson Tirelli
> JBoss Drools Core Development
> Office: +55 11 3529-6000
> Mobile: +55 11 9287-5646
> JBoss, a division of Red Hat @ www.jboss.com
> _______________________________________________
> rules-users mailing list
> rules-users(a)lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users
>
>
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--
Edson Tirelli
JBoss Drools Core Development
Office: +55 11 3529-6000
Mobile: +55 11 9287-5646
JBoss, a division of Red Hat @ www.jboss.com