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Posted to dev@commons.apache.org by Andy Malakov <an...@transdecisions.com> on 2004/01/28 20:14:46 UTC
[collections] new feature request: org.apache.commons.collections.map.ReferenceMap (WeakIdentityHashMap)
Hello All,
I would like to ask your opinion on providing WeakIdentityHashMap features to ReferenceMap.
Object cache is often implemented using ReferenceMap (WeakHashMap). This class delegates decision on when to de-cache an objects on
Java GC.
In many systems Java objects that represent database instances use database identity: methods Object.equals(Object) and
Object.hashCode() are redefined to use database identity (identity defined in terms of object table + object primary keys).
When traditional java.util.Map is used to implement database caches different instances of the same database objects present a
problem: instances override each other. Class java.util.IdentityHashMap (Apache Collections 3.0: IdentityMap) can be used to solve
this problem - this approach uses System.identityHashCode() to obtain reference hashCode and Java comparison operator to compare
keys (and values).
What I need is functionality of IdentityMap combined with WeakReference-based keys.
Is it possible to extend ReferenceMap with an ability to use reference identity instead of object identity? I can send you my
prototype if you are interested (it adds about ten lines of code to ReferenceMap).
Here are some links to Sun's bug parade pages that describe similar feature request for Java's java.util.WeakHashMap:
http://developer.java.sun.com/developer/bugParade/bugs/4809420.html
http://developer.java.sun.com/developer/bugParade/bugs/4500542.html
P.S. There is a need for this feature in Apache DB-OJB project.
All the Best,
Andy
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Re: [collections] new feature request: org.apache.commons.collections.map.ReferenceMap (WeakIdentityHashMap)
Posted by Andy Malakov <an...@transdecisions.com>.
Thanks Stephen.
Here is the ticket: http://nagoya.apache.org/bugzilla/show_bug.cgi?id=26503.
All the Best,
Andy
----- Original Message -----
From: "Stephen Colebourne" <sc...@btopenworld.com>
To: "Jakarta Commons Developers List" <co...@jakarta.apache.org>
Sent: Wednesday, January 28, 2004 3:18 PM
Subject: Re: [collections] new feature request: org.apache.commons.collections.map.ReferenceMap (WeakIdentityHashMap)
> The ideal solution IMO would be for ReferenceMap to extend the new
> AbstractHashedMap class. I wanted to do this but ran out of time before 3.0.
> If this was done, the identity part becomes natural in the same way as the
> IdentityMap works.
>
> The alternative solution is to just tweak ReferenceMap as you are
> suggesting. I reckon the best thing to do is to open a bugzilla ticket and
> attach your code, so we can see.
>
> Whatever, it seems like a good addition.
>
> Stephen
>
>
> ----- Original Message -----
> From: "Andy Malakov" <an...@transdecisions.com>
> > I would like to ask your opinion on providing WeakIdentityHashMap features
> to ReferenceMap.
> >
> >
> > Object cache is often implemented using ReferenceMap (WeakHashMap). This
> class delegates decision on when to de-cache an objects on
> > Java GC.
> >
> > In many systems Java objects that represent database instances use
> database identity: methods Object.equals(Object) and
> > Object.hashCode() are redefined to use database identity (identity defined
> in terms of object table + object primary keys).
> >
> > When traditional java.util.Map is used to implement database caches
> different instances of the same database objects present a
> > problem: instances override each other. Class java.util.IdentityHashMap
> (Apache Collections 3.0: IdentityMap) can be used to solve
> > this problem - this approach uses System.identityHashCode() to obtain
> reference hashCode and Java comparison operator to compare
> > keys (and values).
> >
> > What I need is functionality of IdentityMap combined with
> WeakReference-based keys.
> >
> > Is it possible to extend ReferenceMap with an ability to use reference
> identity instead of object identity? I can send you my
> > prototype if you are interested (it adds about ten lines of code to
> ReferenceMap).
> >
> >
> >
> > Here are some links to Sun's bug parade pages that describe similar
> feature request for Java's java.util.WeakHashMap:
> >
> > http://developer.java.sun.com/developer/bugParade/bugs/4809420.html
> > http://developer.java.sun.com/developer/bugParade/bugs/4500542.html
> >
> > P.S. There is a need for this feature in Apache DB-OJB project.
> >
> > All the Best,
> > Andy
> >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: commons-dev-unsubscribe@jakarta.apache.org
> > For additional commands, e-mail: commons-dev-help@jakarta.apache.org
>
>
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>
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Re: [collections] new feature request: org.apache.commons.collections.map.ReferenceMap (WeakIdentityHashMap)
Posted by Stephen Colebourne <sc...@btopenworld.com>.
The ideal solution IMO would be for ReferenceMap to extend the new
AbstractHashedMap class. I wanted to do this but ran out of time before 3.0.
If this was done, the identity part becomes natural in the same way as the
IdentityMap works.
The alternative solution is to just tweak ReferenceMap as you are
suggesting. I reckon the best thing to do is to open a bugzilla ticket and
attach your code, so we can see.
Whatever, it seems like a good addition.
Stephen
----- Original Message -----
From: "Andy Malakov" <an...@transdecisions.com>
> I would like to ask your opinion on providing WeakIdentityHashMap features
to ReferenceMap.
>
>
> Object cache is often implemented using ReferenceMap (WeakHashMap). This
class delegates decision on when to de-cache an objects on
> Java GC.
>
> In many systems Java objects that represent database instances use
database identity: methods Object.equals(Object) and
> Object.hashCode() are redefined to use database identity (identity defined
in terms of object table + object primary keys).
>
> When traditional java.util.Map is used to implement database caches
different instances of the same database objects present a
> problem: instances override each other. Class java.util.IdentityHashMap
(Apache Collections 3.0: IdentityMap) can be used to solve
> this problem - this approach uses System.identityHashCode() to obtain
reference hashCode and Java comparison operator to compare
> keys (and values).
>
> What I need is functionality of IdentityMap combined with
WeakReference-based keys.
>
> Is it possible to extend ReferenceMap with an ability to use reference
identity instead of object identity? I can send you my
> prototype if you are interested (it adds about ten lines of code to
ReferenceMap).
>
>
>
> Here are some links to Sun's bug parade pages that describe similar
feature request for Java's java.util.WeakHashMap:
>
> http://developer.java.sun.com/developer/bugParade/bugs/4809420.html
> http://developer.java.sun.com/developer/bugParade/bugs/4500542.html
>
> P.S. There is a need for this feature in Apache DB-OJB project.
>
> All the Best,
> Andy
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: commons-dev-unsubscribe@jakarta.apache.org
> For additional commands, e-mail: commons-dev-help@jakarta.apache.org
---------------------------------------------------------------------
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