[infinispan-dev] Preliminary implementation for ISPN-244 and improvement suggestions.

[Galder Zamarreño]

On Dec 7, 2010, at 7:06 PM, Manik Surtani wrote:

> All looks great.  +1 to annotating externalizers rather than the class being externalized, but how would you match them up?  When the marshalling framework sees Class clazz, would it try and match the classes using clazz.equals()?  We'd need to consider class loader implications...

Hmmm, not sure I understand your question, but lemme explain what happens right now regardless of the suggestion below. 

On startup, ConstantObjectTable reads the current marshallable configuration (id, type class and externalizer class) and based on that it populates two maps:

- First, an IdentityHashMap mapping type classes to their corresponding Externalizer instances. This is used at writing time. Actually, good thing I'm explaining this, cos since we know support user defined classes, that needs to be WeakHashMap to avoid leaking user defined Class instances. Class equality is based on reference equality.

- Second map links up Externalizer id numbers to corresponding Externalizer instances. This is used at read time to figure out the Externalizer to use to read the stream.

We should not have classloading issues as long as I change from IdentityHashMap to WeakHashMap for Class keyed map.

> 
> 
> +1 to making the config easier too.
> 
> 
> On 7 Dec 2010, at 09:49, Galder Zamarreño wrote:
> 
>> Hi all,
>> 
>> Re: https://jira.jboss.org/browse/ISPN-244
>> 
>> This is trunk now and I've written preliminary documentation for it in http://community.jboss.org/docs/DOC-16198. Have a read through it and let me know what you think.
>> 
>> Now, there's a couple of improvements I'm considering doing even for alpha1:
>> 
>> 1. Internally, Infinispan has been mapping Externalizer classes and the types they marshall via @Marshallable interface. I don't think this annotation is really usable as it is for users cos there can be situations where users might not be able to modify the class that they wanna serialize. However, they for sure should be able to modify the Externalizer implementation classes, so I was wondering of converting this annotation into an annotation that an Externalizer class takes and that specifies the type of class that it externalizes and its id. Example:
>> 
>> class Person {
>> ...
>> }
>> 
>> @Marshalls(typeClass=Person.class, id=768)
>> class PersonExternalizer Implements Externalizer<Person> {
>> ...
>> }
>> 
>> This could be a mechanism that could be used in equal manner by both internal and user defined externalizers. We don't wanna be doing annotation scanning, so in the same fashion that for internal externalizers we list the type classes that can be extermalized, this could lead to a user configuration simplification, i.e:
>> 
>> <global>
>> <serialization>
>>   <externalizers>
>>     <externalizer class="PersonExternalizer" />
>>   </externalizers>
>> </serialization>
>> </global>
>> 
>> On startup we'd load the externalizers defined in configuration and search for the @Marshalls annotation which would give us the rest of info which is: typeClass and id. Thoughts?? I think this would make internal and user defined externalizers more homogeneous when it comes to their definition and would simplify configuration.
>> 
>> Chaging @Marshallable to @Marshalls should be easy to do particularly cos this annotation was only used for internal purpouses.
>> 
>> 2. The second improvement I had in mind is around programmatic configuration. As you can see in the docu, configuring programmatically user defined externalizers requires quite a bit of code. I was thinking of adding a helper method in global configuration that would hide all of that away. If you take in account my recommendations for the previous point, that would be limited to something along the lines of:
>> 
>> globalCfg.addExternalizer(PersonExternalizer.class);
>> 
>> Where the method would have a signature like: public void addExternalizer(Class<? externds Externalizer> externalizerClass);
>> 
>> We could also have an alternative that uses reflection to load the class and add it: public void addExternalizer(String externalizerClassName);
>> 
>> Cheers,
>> --
>> Galder Zamarreño
>> Sr. Software Engineer
>> Infinispan, JBoss Cache
>> 
>> 
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> 
> --
> Manik Surtani
> manik at jboss.org
> Lead, Infinispan
> Lead, JBoss Cache
> http://www.infinispan.org
> http://www.jbosscache.org
> 
> 
> 
> 
> 
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--
Galder Zamarreño
Sr. Software Engineer
Infinispan, JBoss Cache