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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 16:38:43 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1063?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12543939
] 

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

In ''code words":
{code}
// Filter F is calling TokenStream ts:
F.next(Token result) {
    Token t = ts.next(result);
    t.setSomething();
    return t;
}
{code}

Problem as described: ts expects the token it returns to not be altered because it somehow
intends to rely on its content when servicing the following call to next([]). In other words,
it assumes that callers to next([]) would only consume, but not alter, the returned token.


Seems that such an expectation by ts would be problematic no matter if ts.next() or ts.next(Token)
are used.

I mean, even if we removed next(Token) but kept Token.termBuffer(), that char array could
be modified, and some TokenSteam implementation could still be broken because it assumes (following
similar logic) that it can reuse its private copy of the char array... right?

{quote}
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.
{quote}

TokenStream already does this, right? (or do you mean in the class TokenStream or in all implementations
of TokenStream?)


> 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
>
>
> 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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