Re: [xml] xpath/xslt memory leak

["William M. Brack" <wbrack mmm com hk>]

Pawe³ Pa³ucha said:
> Hi,
> I think I've found a nice memory leak. I'm using xslt to reproduce it, but I
> think that bug is in xpath module, so I send it here.

I don't think there is any such thing as a "nice" memory leak - leaks are bad,
bad, bad...

I'm working on the problem, but I'm not going to be able to continue for a few
days, so I thought I better reply in order to confirm your report.

> The program is just transforming simple document in loop:

I can reproduce the leak using xsltproc, so there is no argument over whether
your program is good or bad.

<snip>
>
> Document (b.xml) is like that:
> <?xml version="1.0"?>
> <params xmlns="http://www.praterm.com.pl/SZARP/ipk";>
>      <param>
>          <raport title="A"/>
>      </param>
> </params>
>
> and stylesheet:
>
> <?xml version="1.0"?>
>
>                                <xsl:stylesheet version="1.0"
>    xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
>    xmlns:ipk="http://www.praterm.com.pl/SZARP/ipk";>
>
>                              <!-- <xsl:param name="title"/> -->
>    <xsl:template match="ipk:params">
>      <xsl:element name="report">
>        <xsl:for-each select="//ipk:param[ipk:raport[ title=$title]]">
>          <xsl:element name="param">
>          </xsl:element>
>        </xsl:for-each>
>      </xsl:element>
>    </xsl:template>
> </xsl:stylesheet>
>
> The stylesheet is somewhat incorrect - declaration of parameter 'title' is
> missing. This simple program keeps allocating more and more memory (can be
> viewed with top/htop). When I uncomment the parameter declaration, everything
> works OK.

I simplified these documents a little - when debugging it's good to get rid of
all the non-esential parts (e.g. namespace isn't involved, etc.).  The missing
variable declaration is certainly a part of the problem.  Here's my reduced
set:

<?xml version="1.0"?>
<params><param/></params>

<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform";>
 <xsl:template match="params">
   <xsl:value-of select="param[ title=$title]"/>
 </xsl:template>
</xsl:stylesheet>

> And, btw - the output from valgrind differs when I use
> '--leak-resolution=high'.
> Checked with 2.6.18, but there's nothing about it in changelog, so I suppose
> its still there.

I'm just using
 valgrind --tool=memcheck --show-reachable=yes --leak-check=yes
--num-callers=15 xsltproc b.xsl b.xml

Problem is present in current CVS.
bill billsuper work $ xsltproc --version
Using libxml 20619-CVS2405, libxslt 10114-CVS1011 and libexslt 812-CVS1011

> Files in attachment for convenience.
>
> Pawe³ Pa³ucha

I'll respond further after I've had a chance to find / fix the problem (of
course, if someone else wants to do some debugging within xpath.c before I can
get back to it, they're certainly welcome to do so :-).  Thanks for the
report.

Bill