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From Vadim Gritsenko <va...@reverycodes.com>
Subject Re: ThreadSafe Transformers
Date Wed, 22 Sep 2004 15:26:22 GMT
Leo Sutic wrote:

> Like the idea (and we can extend it to Generators, Serializers, etc.), but:
> 
> Instinctively dislike the hack in the component selector.

Alternatively, it could be done by implementing custom ComponentHandler 
(extend DefaultComponentHandler?) from o.a.a.excalibur.component, but it 
looks more involved from whatever is described below.

And keep in mind that ComponentSelector from o.a.c.c.t.sitemap is 
selector specifically for sitemap components...

Vadim


> /LS
> 
> On Wed, 22 Sep 2004 10:31:01 -0400, Vadim Gritsenko
> <vadim@reverycodes.com> wrote:
> 
>>Y'all,
>>
>>Some time ago I remember discussions about making transformers
>>threadsafe, major changes, about Cocoon 3, etc. Yesterday it occured to
>>me that Transformers can easily be made ThreadSafe with only additions
>>to current Cocoon architecture without any major rewrites. It can be
>>done in this way:
>>
>>Add new interface marking threadsafe transformer:
>>    public interface TransformerFactory {
>>        Transformer getTransformer();
>>    }
>>
>>Override select method in ComponentSelector:
>>    public Component select(Object hint) throws ComponentException {
>>        Component component = super.select(hint);
>>        if (this.roleId == TRANSFORMER) {
>>            if (component instanceof TransformerFactory) {
>>                return ((TransformerFactory)component).getTransformer();
>>            }
>>        }
>>
>>        return component;
>>    }
>>(it is in org.apache.cocoon.components.treeprocessor.sitemap package)
>>
>>Modify existing transformer so that transformer class implements
>>TransformerFactory, ThreadSafe, and nested class TransformerImpl
>>implements Transformer, CacheableProcessingComponent (and it can extend
>>AbstractXMLPipe). On the example of EncodeURLTransformer:
>>    public class EncodeURLTransformer
>>        implements TransformerFactory, Configurable, ThreadSafe {
>>
>>        public void configure(Configuration config) {...}
>>
>>        public Transformer getTransformer() {
>>            return new TransformerImpl();
>>        }
>>
>>        private class TransformerImpl
>>            extends AbstractTransformer
>>            implements CacheableProcessingComponent {
>>
>>            public void setup(SourceResolver resolver,
>>                              Map objectModel,
>>                              String source,
>>                              Parameters parameters) {...}
>>
>>            public Serializable getKey() {...}
>>
>>            public SourceValidity getValidity() {...}
>>
>>            public void startElement(String uri,
>>                                     String name,
>>                                     String raw,
>>                                     Attributes attributes) {...}
>>            ...
>>        }
>>    }
>>
>>Thus ThreadSafe transformer is a factory creating instances of SAX pipes
>>performing actual transformation. Pluses of this approach, as I see it, are:
>> * Transformer is <init>ed / contextualize()d / service()ed /
>>   configure()d / etc just once. Saves CPU cycles.
>> * Transformer global configuration / context / components
>>   stored in single instance of ThreadSafe transformer instead
>>   of beeing copied in each instance of usual pooled
>>   transformer. Saves memory.
>> * Users of ComponentSelector still receive instance of
>>   Transformer as they used to expect. Backward compatibility.
>>
>>Now question; is it a good idea to check in this code into 2.2? Any
>>drawbacks of this approach?
>>
>>Thanks,
>>Vadim


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