RE: [xsl] loop timing and result-document flush

["Michael Kay" <mike@xxxxxxxxxxxx>]

Could I attempt a summary?

Firstly, as David C pointed out, for-each is not a loop. Think of it as
processing all the items in parallel, even if the implementation chooses to
do it sequentially.

Secondly, you're not allowed to read a document that was written earlier in
the transformation. That applies to doc-available() just as much as to
doc().

Thirdly, and this has also been said already, though perhaps not very
clearly: your problem description essentially says that you are eliminating
duplicates, and the right tools for that job in XSLT 2.0 are
distinct-values() and xsl:for-each-group.

Fourthly, your strategy doesn't work because doc-available() is defined to
be stable. Once you've called doc-available('abc.xml') and have received the
answer "false", the system is obliged to continue returning the answer false
if you call the function again with the same argument. [That's the way it is
supposed to work. To be honest, I'm pleasantly surprised Saxon is getting
this right, and I wouldn't guarantee that it will do so in all
circumstances!]

Michael Kay
http://www.saxonica.com/ 

> -----Original Message-----
> From: Duane Gran [mailto:dmg2n@xxxxxxxxxxxx] 
> Sent: 02 May 2007 15:06
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: [xsl] loop timing and result-document flush
> 
> XSL experts,
> 
> I have an XSL which loops over a set of elements in search of 
> links and creates a result document for the link.  In some 
> cases there is more than one link to the same anticipated 
> document, so I use the doc-
> available() to test first for its existence before creating 
> the file.  This is intended to avoid a DynamicError related 
> to writing more than one result document to the same URI.
> 
> However, when I run the program against a large set of 
> documents after 10 minutes or so I get the DynamicError.  
> Below is the output (run via ant) along with some debugging 
> fields I'll explain in a moment:
> 
>       [xslt]         test for doc /Users/dgran/dev/rose/build/zoom/ 
> 1-1861.wrenn.320-321.img.html  available: false
>       [xslt]           creating file: /Users/dgran/dev/rose/build/ 
> zoom/1-1861.wrenn.320-321.img.html
> 
>       [xslt]         test for doc /Users/dgran/dev/rose/build/zoom/ 
> 1-1861.wrenn.320-321.img.html  available: false
>       [xslt]           creating file: /Users/dgran/dev/rose/build/ 
> zoom/1-1861.wrenn.320-321.img.html
> 
>       [xslt] Failed to process /Users/dgran/dev/rose/deploy.temporary/
> 1-1861.wrenn.rad.xml
> 
> BUILD FAILED
> /Users/dgran/dev/rose/build.xml:395: The following error 
> occurred while executing this line:
> /Users/dgran/dev/rose/build.xml:77: net.sf.saxon.trans.DynamicError:  
> Cannot write more than one result document to the same URI: 
> file:/ Users/dgran/dev/rose/build/zoom/1-1861.wrenn.320-321.img.html
> 
> In the first case, the file (1-1861.wrenn.320-321.img.html) 
> is correctly created because it doesn't exist yet.  In the 
> second case the doc-available() method should return true and 
> skip the result- document command, but it fails to work.  My 
> hypothesis is that the
> result-document() method isn't finished flushing before the call to
> doc-available() is made.
> 
> Assuming my guess is correct, is there a way in XSL to assure 
> that the document is finished writing before continuing to 
> the next iteration in the loop?  Maybe there is another way 
> of skinning this cat.  I welcome suggestions.  I'm using 
> Saxon 8-7-3j.  Below is a simplified version of my stylesheet:
> 
> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform";  
> version="2.0">
>    <xsl:template match="/">
>      <xsl:for-each select="ram|//repro|//page|//figure">
>        <xsl:variable name="zoomhtml">
>          <xsl:text>build/zoom/</xsl:text>
>          <xsl:value-of select="@image"/>
>          <xsl:text>.img.html</xsl:text>
>        </xsl:variable>
>        <xsl:message>
>          test for doc <xsl:value-of select="$zoomhtml"/>  available:  
> <xsl:value-of select="doc-available($zoomhtml)"/>
>        </xsl:message>
>        <xsl:choose>
>          <xsl:when test="doc-available($zoomhtml)"/>
>          <xsl:otherwise>
>            <xsl:message> creating file: <xsl:value-of 
> select="$zoomhtml"/>
>            </xsl:message>
>            <xsl:result-document href="$zoomhtml"> 
> </xsl:result-document>
>          </xsl:otherwise>
>        </xsl:choose>
>      </xsl:for-each>
>    </xsl:template>
> </xsl:stylesheet>
> 
> Duane Gran