Deborah Pickett wrote:
True, though years of multithread programming has taught me a strong
aversion to the inherent race condition in non-atomic test-and-create
operations like this. It can't possibly be as big a risk as hash
collision, but it doesn't stop me feeling any less dirty.
As always, perfection is impossible, so ultimately it comes down to how
much effort I am willing to go to for that extra nine of reliability.
From another angle, not sure whether your system allows this, but
getting a unique filename, or a unique number or whatever, without the
use of non-XSLT functions, becomes inherently easy if you can use some
internet service. In other words: if you can allow for a dependency to
some internet (intranet or even localhost) web site, you can use that
for creating a guaranteed-unique name, possibly with the information of
your original filename.
For instance, I found one internet service that returns a UUID. You can
do about the same with any method of uniqueness you want:
<xsl:template match="/"
xpath-default-namespace="http://www.w3.org/1999/xhtml";>
<xsl:variable name="filename"
select="doc('http://www.famkruithof.net/uuid/uuidgen')/html/body/table/tr/td/h3[1]"
/>
<xsl:result-document href="{$filename}" >...</xsl:result-document>
</xsl:template>
(code tested)
Setting up a system to provide a UUID is as simple as using any Windows
2000 or higher machine, using the following the VBScript (and I am sure
something equally easy can be done in a Unix-like environment) and put
it somewhere in the path of IIS. And if you don't like the UUID syntax,
you can send a parameter along with the filename and let it be MD5'ed,
of course ;)
' VBScript to create a UUID:
Set TypeLib = CreateObject("Scriptlet.TypeLib")
NewGUID = TypeLib.Guid
WScript.Echo(left(NewGUID, len(NewGUID)-2))
Cheers,
-- Abel Braaksma
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