The following comment has been added to this issue:
Author: Rafal Krzewski
Created: Wed, 26 May 2004 4:34 AM
Body:
Memory dump contents are available at http://caltha.pl/~rafal/java.hprof.txt.bz2 23MB,
350MB after uncompressing.
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View this comment:
http://jira.codehaus.org/browse/MAVEN-1294?page=comments#action_20077
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View the issue:
http://jira.codehaus.org/browse/MAVEN-1294
Here is an overview of the issue:
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Key: MAVEN-1294
Summary: Maven is leaking much memory
Type: Bug
Status: Unassigned
Priority: Major
Original Estimate: Unknown
Time Spent: Unknown
Remaining: Unknown
Project: maven
Components:
jelly/ant integration
Versions:
1.0-rc3
Assignee:
Reporter: Rafal Krzewski
Created: Wed, 26 May 2004 4:13 AM
Updated: Wed, 26 May 2004 4:34 AM
Description:
The test was done as follows. I took ledge-components project
http://objectledge.org/modules/ledge-components, cleaned out the target, then ran
statcvs goal. Statcvs generated 160 xdoc documents, 2.2MB of markup total. Then I ran
xdocs goal, to tranfrom the xdocs into html, under hprof profiler build into JDK.
Settings were: allocation site analysis, heap dump at exit, stacktrace depth 16. The
run took about 65 minutes on Athlon 1700XP, 512 phisical RAM. Maximum memory usage was
530MB virtual/240MB resident during the run, it surged some additional 300MB both
during heap dump. The generated dump file is about 350MB, 23MB when bzip2 compressed.
I'm going to post an xls file on Jira containg the statistics of objects allocated,
and objects alive at the time of VM generation. From what I'm seeing none of the Jelly
TagScript objects created gets ever garbage collected. Wading through the heap dump I
was able to determine that all of them are connected to the GC root through the main
Thread, and a ThreadLocal variable tagHolder declared in jelly's TagScript.java, line
115. Despite calls to tagHolder.set(null), the TagScript object stays connected to the
Thread by means of ThreadLocal$ThreadLocalMap$Entry object which is a subclass of
java.lang.ref.WeakReference. ThreadLocal implementation in JDK works like that. Now,
AFAIK the GC is free to harvest all objects that are not connected to a GC root
through hard reference, or a SoftReference. I wasn't able to trace all references in
the object graph regarding TagScript objects (there are 21k+ of them!) so I am not
sure if there are any other references that connect the TagScripts to a GC root
through a permanent refernce, like a static field in some class. I cant tell you it's
a dog's work to do that by hand. If I only had a proper memory analysys tool! Alas all
the good ones are commercial... On the other hand GC is not *required* to harvest
these objects. Maybe it just didn't bother to harvest because it was not pressed for
memory? In my test it had still many megabytes left. Maybe a better test would be
running it with too few memory and checking what was left alive, despite the fact GC
was desperate to find the space?
At any rate, TagScript.tagHolder is suspicious, and if it's even not the culprit
itself (could be if WeakRefernce implementation was broken) it is hiding the real
problem (at least in the environment of my test). Note that the variable is not
static, which means all TagScript object instances get tied to the Thread. I don't
know if the possibility of using each instance concurrently from multiple threads is
useful at all, especially that the instances have more state information, not only the
tagHolder... Anyway, it's a wrong forum to discuss that. I also heard that Jelly was
abandoned by the original author so there is a good chance that noone understands why
this tagHolder thingy was introduced and what it does...
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