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From "Doron Cohen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1063) Token re-use API breaks back compatibility in certain TokenStream chains
Date Tue, 20 Nov 2007 20:52:43 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1063?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12544059
] 

Doron Cohen commented on LUCENE-1063:
-------------------------------------

{quote}
and even with old style Tokens w/o Token reuse, one could always change what string the token
pointed at.
{quote}

...right... termText is now private but it used to be package protected. 

Patch looks good for (default) TokenStream,
though it is a shame there is no magic way to know if Token was changed and is copying really
required.

But is this good enough also for non default TokenStreams which imlpement next(Token)? 
mm.. I checked next(Token res) implementations of CharTokenizer, KeywordTokenizer and StandardTokenizer
and non of them checks res for null.
Am I missing something trivial?

> Token re-use API breaks back compatibility in certain TokenStream chains
> ------------------------------------------------------------------------
>
>                 Key: LUCENE-1063
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1063
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Analysis
>    Affects Versions: 2.3
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: 2.3
>
>         Attachments: LUCENE-1063.patch
>
>
> In scrutinizing the new Token re-use API during this thread:
>   http://www.gossamer-threads.com/lists/lucene/java-dev/54708
> I realized we now have a non-back-compatibility when mixing re-use and
> non-re-use TokenStreams.
> The new "reuse" next(Token) API actually allows two different aspects
> of re-use:
>   1) "Backwards re-use": the subsequent call to next(Token) is allowed
>      to change all aspects of the provided Token, meaning the caller
>      must do all persisting of Token that it needs before calling
>      next(Token) again.
>   2) "Forwards re-use": the caller is allowed to modify the returned
>      Token however it wants.  Eg the LowerCaseFilter is allowed to
>      downcase the characters in-place in the char[] termBuffer.
> The forwards re-use case can break backwards compatibility now.  EG:
> if a TokenStream X providing only the "non-reuse" next() API is
> followed by a TokenFilter Y using the "reuse" next(Token) API to pull
> the tokens, then the default implementation in TokenStream.java for
> next(Token) will kick in.
> That default implementation just returns the provided "private copy"
> Token returned by next().  But, because of 2) above, this is not
> legal: if the TokenFilter Y modifies the char[] termBuffer (say), that
> is actually modifying the cached copy being potentially stored by X.
> I think the opposite case is handled correctly.
> A simple way to fix this is to make a full copy of the Token in the
> next(Token) call in TokenStream, just like we do in the next() method
> in TokenStream.  The downside is this is a small performance hit.  However
> that hit only happens at the boundary between a non-reuse and a re-use
> tokenizer.

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