When working on IvyDE's build to get dependencies from Eclipse mirrors, I tried
to use resourcelist, as documented in the examples of the doc [1].
But it was very slow because Ant is checking every urls and some mirrors are
not very responsive. So I had to workaround and filter the urls to select only
the first one and hoping it is available:
<copy todir="${basedir}">
<first>
<restrict>
<resourcelist>
<!-- get the xml mirror list -->
<url
url="${hudson.download.baseurl}?fi...@{dropdir}/@{file}&protocol=http&format=xml"
/>
<filterchain> <!-- change the xml into flat url list -->
<linecontainsregexp>
<regexp pattern="^.*mirror
url="([^"]*)".*$" />
</linecontainsregexp>
<tokenfilter>
<replaceregex pattern="^.*mirror
url="([^"]*)".*$" replace="\1" flags="gi" />
</tokenfilter>
<headfilter lines="1" /> <!-- HACK to force Ant to not
check every urls -->
</filterchain>
</resourcelist>
<exists/> <!-- restrict to only responsive mirror-->
</restrict>
</first> <!-- copy the first responsive one -->
<flattenmapper/> <!-- avoid the useless creation of folders-->
</copy>
I looked into the code, it seems org.apache.tools.ant.types.resources.Restrict
is the culprit. It uses BaseResourceCollectionWrapper which loads the entire
underlying resource collection.
I searched for the use of BaseResourceCollectionWrapper in Ant and I think that
this performance issue may also affect
org.apache.tools.ant.types.resources.SizeLimitCollection and
org.apache.tools.ant.types.resources.Tokens.
I started to think about a fix but it seems non trivial. If I'm not mistaken we
would have to implement an iterator which should deal with an optionnal cache
and concurrency.
I am also worried about the isFilesystemOnly implementation in Restrict. Should
it return true if actually selected resources are files, or return true if the
entire set of candidates are files ? In the first case it would make the
iterator useless.
Side note: I didn't checked that piece of script in as our Hudson instance
doesn't have Ant 1.8 installed. Not yet. I'll ask for it.
Nicolas
[1] http://ant.apache.org/manual/Types/resources.html#resourcelist
PS: I started recently to intensively use loadresource and all the resource
related stuff in my build scripts, it is amazingly porwerful ! It reminds me
when I was 'pipelining' in cocoon ;)
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