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From "Michael Busch (JIRA)" <>
Subject [jira] Commented: (LUCENE-1422) New TokenStream API
Date Thu, 13 Nov 2008 17:48:46 GMT


Michael Busch commented on LUCENE-1422:

Looks good! 
Thanks for reviewing ... again!

I'm a little confused by 'start' and 'initialize' in TokenStream.
Good question. The only reason why I added two separate methods here was to enforce that TokenFilter#start()
always calls input.start() first. I think otherwise this will be a pitfall for people who
want to implement their own filters and override start(). (happened to me when I modified
the tests a couple of times)
On the other hand I agree that Three methods (start(), initialize(), reset()) are confusing.
I guess we can deprecate reset() in the future and have start() rewind the stream if supported
by the stream. (I think you mentioned a boolean method could return true if rewind is supported?)
So I'd be ok with collapsing start/initialize into one method if you prefer that. I'd just
have to add an explicit warning to the javadocs in TokenFilter.

I'm seeing this failure (in test I just committed this AM). I think
it's OK, because the new API is enabled for all tests and I'm using
the old API with that analyzer?
Yeah, I've to modify the new test to use the new API.

- BackCompatTokenStream is calling attributes.put directly but all
others use super's addAttribute.
- Why is BackCompatTokenStream overriding so many methods? EG
has/get/addAttribute - won't super do the same thing?
I had a different implementation of BCTS, so this is left-over. Of course you're right, I
can simplify that class.

Maybe add reasons to some of the asserts, eg StopFilter has
"assert termAtt != null", so maybe append to that ": initialize()
wasn't called".
Yeah good idea, will do.

> New TokenStream API
> -------------------
>                 Key: LUCENE-1422
>                 URL:
>             Project: Lucene - Java
>          Issue Type: New Feature
>          Components: Analysis
>            Reporter: Michael Busch
>            Assignee: Michael Busch
>            Priority: Minor
>             Fix For: 2.9
>         Attachments: lucene-1422-take4.patch, lucene-1422-take5.patch, lucene-1422.patch,
lucene-1422.take2.patch, lucene-1422.take3.patch, lucene-1422.take3.patch
> This is a very early version of the new TokenStream API that 
> we started to discuss here:
> This implementation is a bit different from what I initially
> proposed in the thread above. I introduced a new class called
> AttributedToken, which contains the same termBuffer logic 
> from Token. In addition it has a lazily-initialized map of
> Class<? extends Attribute> -> Attribute. Attribute is also a
> new class in a new package, plus several implementations like
> PositionIncrementAttribute, PayloadAttribute, etc.
> Similar to my initial proposal is the prototypeToken() method
> which the consumer (e. g. DocumentsWriter) needs to call.
> The token is created by the tokenizer at the end of the chain
> and pushed through all filters to the end consumer. The 
> tokenizer and also all filters can add Attributes to the 
> token and can keep references to the actual types of the
> attributes that they need to read of modify. This way, when
> boolean nextToken() is called, no casting is necessary.
> I added a class called TestNewTokenStreamAPI which is not 
> really a test case yet, but has a static demo() method, which
> demonstrates how to use the new API.
> The reason to not merge Token and TokenStream into one class 
> is that we might have caching (or tee/sink) filters in the 
> chain that might want to store cloned copies of the tokens
> in a cache. I added a new class NewCachingTokenStream that
> shows how such a class could work. I also implemented a deep
> clone method in AttributedToken and a 
> copyFrom(AttributedToken) method, which is needed for the 
> caching. Both methods have to iterate over the list of 
> attributes. The Attribute subclasses itself also have a
> copyFrom(Attribute) method, which unfortunately has to down-
> cast to the actual type. I first thought that might be very
> inefficient, but it's not so bad. Well, if you add all
> Attributes to the AttributedToken that our old Token class
> had (like offsets, payload, posIncr), then the performance
> of the caching is somewhat slower (~40%). However, if you 
> add less attributes, because not all might be needed, then
> the performance is even slightly faster than with the old API.
> Also the new API is flexible enough so that someone could
> implement a custom caching filter that knows all attributes
> the token can have, then the caching should be just as 
> fast as with the old API.
> This patch is not nearly ready, there are lot's of things 
> missing:
> - unit tests
> - change DocumentsWriter to use new API 
>   (in backwards-compatible fashion)
> - patch is currently java 1.5; need to change before 
>   commiting to 2.9
> - all TokenStreams and -Filters should be changed to use 
>   new API
> - javadocs incorrect or missing
> - hashcode and equals methods missing in Attributes and 
>   AttributedToken
> I wanted to submit it already for brave people to give me 
> early feedback before I spend more time working on this.

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