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Date: Sat, 18 Jul 2009 04:06:14 -0700 (PDT)
From: "Uwe Schindler (JIRA)" <jira@apache.org>
To: java-dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-1693) AttributeSource/TokenStream API
 improvements
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    [ https://issues.apache.org/jira/browse/LUCENE-1693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12732878#action_12732878 ] 

Uwe Schindler commented on LUCENE-1693:
---------------------------------------

In this case we should rename TeeSink to something like SplitTokenStream (which does not extend TokenStream). One could get then any number of "sinks" from it:

{code}
SplitTokenFilter splitter=new SplitTokenStream(stream); // does not extend TokenStream!!!
TokenStream stream1=splitter.newSinkTokenStream();
TokenStream stream2=splitter.newSinkTokenStream();
...
{code}

In this case the caching would be done directly in the splitter and the sinks are only consumers. The first sink that calls to get the attribute states forces the splitter to harvest and cache the input stream (exactly like CachingTokenStream does it). In principle it would be the same like a CachingTokenStream.

But on the other hand: You can always create a CachingTokenStream and reuse the same instance for different fields. Because the indexer always calls reset() before consuming, you could re-read it easily. Any additional filters could then plugged in front for each field. In this case the order is not important:

{code}
TokenStream stream=new CachingTokenStream(input);
doc.add(new Field("xyz", new DoSomethingTokenFilter(stream);
doc.add(new Field("abc", new DoSometingOtherTokenFilter(stream);
...
{code}

This would not work, if the indexer can consume the different fields in parallel. But with the current state it would even not work with Tee/Sink (not multithread compatible).

> AttributeSource/TokenStream API improvements
> --------------------------------------------
>
>                 Key: LUCENE-1693
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1693
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Analysis
>            Reporter: Michael Busch
>            Assignee: Michael Busch
>            Priority: Minor
>             Fix For: 2.9
>
>         Attachments: LUCENE-1693.patch, lucene-1693.patch, LUCENE-1693.patch, lucene-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, lucene-1693.patch, TestAPIBackwardsCompatibility.java, TestCompatibility.java, TestCompatibility.java, TestCompatibility.java, TestCompatibility.java
>
>
> This patch makes the following improvements to AttributeSource and
> TokenStream/Filter:
> - removes the set/getUseNewAPI() methods (including the standard
>   ones). Instead by default incrementToken() throws a subclass of
>   UnsupportedOperationException. The indexer tries to call
>   incrementToken() initially once to see if the exception is thrown;
>   if so, it falls back to the old API.
> - introduces interfaces for all Attributes. The corresponding
>   implementations have the postfix 'Impl', e.g. TermAttribute and
>   TermAttributeImpl. AttributeSource now has a factory for creating
>   the Attribute instances; the default implementation looks for
>   implementing classes with the postfix 'Impl'. Token now implements
>   all 6 TokenAttribute interfaces.
> - new method added to AttributeSource:
>   addAttributeImpl(AttributeImpl). Using reflection it walks up in the
>   class hierarchy of the passed in object and finds all interfaces
>   that the class or superclasses implement and that extend the
>   Attribute interface. It then adds the interface->instance mappings
>   to the attribute map for each of the found interfaces.
> - AttributeImpl now has a default implementation of toString that uses
>   reflection to print out the values of the attributes in a default
>   formatting. This makes it a bit easier to implement AttributeImpl,
>   because toString() was declared abstract before.
> - Cloning is now done much more efficiently in
>   captureState. The method figures out which unique AttributeImpl
>   instances are contained as values in the attributes map, because
>   those are the ones that need to be cloned. It creates a single
>   linked list that supports deep cloning (in the inner class
>   AttributeSource.State). AttributeSource keeps track of when this
>   state changes, i.e. whenever new attributes are added to the
>   AttributeSource. Only in that case will captureState recompute the
>   state, otherwise it will simply clone the precomputed state and
>   return the clone. restoreState(AttributeSource.State) walks the
>   linked list and uses the copyTo() method of AttributeImpl to copy
>   all values over into the attribute that the source stream
>   (e.g. SinkTokenizer) uses. 
> The cloning performance can be greatly improved if not multiple
> AttributeImpl instances are used in one TokenStream. A user can
> e.g. simply add a Token instance to the stream instead of the individual
> attributes. Or the user could implement a subclass of AttributeImpl that
> implements exactly the Attribute interfaces needed. I think this
> should be considered an expert API (addAttributeImpl), as this manual
> optimization is only needed if cloning performance is crucial. I ran
> some quick performance tests using Tee/Sink tokenizers (which do
> cloning) and the performance was roughly 20% faster with the new
> API. I'll run some more performance tests and post more numbers then.
> Note also that when we add serialization to the Attributes, e.g. for
> supporting storing serialized TokenStreams in the index, then the
> serialization should benefit even significantly more from the new API
> than cloning. 
> Also, the TokenStream API does not change, except for the removal 
> of the set/getUseNewAPI methods. So the patches in LUCENE-1460
> should still work.
> All core tests pass, however, I need to update all the documentation
> and also add some unit tests for the new AttributeSource
> functionality. So this patch is not ready to commit yet, but I wanted
> to post it already for some feedback. 

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