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From: "Mat McGowan" <mat@nynodata.no>
To: <commons-dev@jakarta.apache.org>
Subject: [jelly] comment - memory leak from using ThreadLocal
Date: Tue, 7 Dec 2004 20:28:17 +0100
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This is quite long so here's an overview:
	- couldn't get jelly CVS HEAD to work with maven 1.0.1
	- from code inspection, seems there may still be a memory leak even
with the fix, possibly because the tests don't exercise all tag types.


After signing in to JIRA, I wanted to a comment to the JIRA issue JELLY-148,
but was denied access, so I'll post it here.

Recent comments requested that people try out the CVS HEAD containing the
memory leak fix. Alas, I couldn't get the latest state to run: With latest
jelly from CVS patched into maven 1.0.1, running maven multiproject fails
with:

    [echo] Generating the Source Xref...
maven-jxr-plugin:report:
    [echo]

BUILD FAILED
File...... E:\Documents and
Settings\mat\.maven\cache\maven-multiproject-plugin-
1.3.1\plugin.jelly
Element... maven:reactor
Line...... 103
Column.... 9
Unable to obtain goal [site] -- E:\Documents and
Settings\mat\.maven\cache\maven
-jxr-plugin-1.4.2\plugin.jelly:94:55: <ant:copy> Warning: Could not find
file R:\stylesheet.css to copy.

This problem doesn't occur with the original jelly jar included in the maven
distribution. (The evaluation of the filename r:\stylesheet.css is incorrect
- it should be several directories down.) I also tried with the CVS HEAD of
jexl incase that was needed as well, but it made no difference. I also tried
replacing the tag-libraries with the latest versions, but no change.)

Anyway, I was also trying to diagnise the memory leak before I'd discovered
a fix was already available. From what I saw, I also wonder if there is
still exists a memory leak, although couldn't look at it fully because of
the regression problem above. When profiling the older jelly code (pre
WeakRefScript as found in maven 1.0.1), from the code, I was expecting all
scripts that are being held from GC by ThreadLocal to be TagScript
instances, but I also found some instances of other script types
(StaticScript, TemplateScript). The only explanation I have is that
TagScript.setTag is being called, which under current CVS HEAD _doesn't_
wrap the tag's script in a weak reference holder, so this may potentially
still cause leaks?

If I could get jelly running with maven, I would have changed
TagScript.setTag to
    protected void setTag(Tag tag) {
        Script body = tag.getBody();
        if (!(body instanceof WeakReferenceWrapperScript))
        {
            tag.setBody(new WeakReferenceWrapperScript(body));
        }
        tagHolder.set(tag);
    }

to see if that helped.

Appologies for the long post.
Regards,
Mat McGowan


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