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Posted to issues@lucy.apache.org by "Nick Wellnhofer (JIRA)" <ji...@apache.org> on 2015/05/16 20:31:00 UTC

[lucy-issues] [jira] [Commented] (CLOWNFISH-44) Immutable Strings can be changed from Perl

    [ https://issues.apache.org/jira/browse/CLOWNFISH-44?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14546886#comment-14546886 ] 

Nick Wellnhofer commented on CLOWNFISH-44:
------------------------------------------

Another note: If we copied string SVs before passing them as arguments, we wouldn't need the clone-on-incref hack. This means that we'd never have to copy string buffers under a COW-enabled Perl.

On the other hand, we also rely on clone-on-incref behavior to ensure thread safety.

> Immutable Strings can be changed from Perl
> ------------------------------------------
>
>                 Key: CLOWNFISH-44
>                 URL: https://issues.apache.org/jira/browse/CLOWNFISH-44
>             Project: Apache Lucy-Clownfish
>          Issue Type: Bug
>          Components: Perl
>            Reporter: Nick Wellnhofer
>            Priority: Minor
>
> Perl can hold a reference to a string passed to Clownfish and subsequently change the string via this reference in a callback. This violates the assumption that Clownfish strings are immutable and can lead to crashes if the string buffer is reallocated.
> This scenario is somewhat contrived but for a proper fix, I think there's no other way than to always copy Perl strings passed as arguments. Fortunately, newer Perls support copy-on-write strings (default since 5.20) which makes this operation cheap.



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