Re: antlibs and classloaders #2

[Peter Reilly]

Jose Alberto Fernandez wrote:
From: Peter Reilly [mailto:[EMAIL PROTECTED] 

I meant to respond to this earlier, but did not get the chance.
1) use of classpath in an antlib.
I have tested using a classpath within an antlib:
~/.ant/lib/x_call.jar containing:
x/antlib.xml
<antlib>
 <typedef resource="x/antlib.xml">
   <classpath path="${user.home}/apps/x/x.jar"/>
 </typedef>
</antlib>
This works fine, but depends on a possible bug in ant
see: bugzilla 28782
http://issues.apache.org/bugzilla/show_bug.cgi?id=28782
The problem is that the typedef in the antlib should pick up 
two antlib.xml resources, the one in  
"${user.home}/apps/x/x.jar" and the one in x_call.jar 
(itself). This will should cause no-ending recursion.

The bug means that this does no happen - the resources in the 
parent classloader are currently not visible to the child 
classloaders.

If the bug is fixed, an infinite recursion will happen.
This could be stopped by typedef checking if it has already 
been executed.  This can be done by using "user" properties - 
but this will pollute the property names, or by exending 
(again) Project to have a map of objects that gets copied to 
its child projects. Using non-user properties or references 
will not work as <*ant*> tasks can stop the non-user 
properties and references being copied to the child 
processes. Using a static map in typedef will not work as 
sibling projects will incorrectly interact.

   

This things sound like we are using the wrong abstraction here.
<typedef/> inside an <antlib/> should use the antlib classloader
as the parent for any subsequent classloader.
 

In this case the parent is the antlib classloader (it is the default 
classloader).

I do not see why that should cause an infinite recursion.
 

The problem is that the <typedef resource="net/.../antlib.xml">
<classpath path="cpptasks.jar"/> </typedef> in
the antlib will pick up the antlib.xml resoure that contains <typedef 
resource="net/.../antlib.xml">
task which will pick up .....,

This does not happen with the current ant code, as the <typedef 
resource="net/.../antlib.xml">
 <classpath path="cpptasks.jar"/></typedef>
task will not see the antlib.xml resource in the parent classloader.

Another way to work-around this is for the typedef to use a thread 
specific stack to check
for recursive loading of xml resources.
This probally should be done in any case:

recursive.xml
<antlib>
  <typedef file="recursive.xml"/>
</antlib>
build.xml:
<project>
 <typedef file="recursive.xml"/>
</project>
Peter
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