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Posted to dev@tomcat.apache.org by bu...@apache.org on 2007/04/19 15:49:00 UTC
DO NOT REPLY [Bug 42172] New: - Classloader leak
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Summary: Classloader leak
Product: Tomcat 5
Version: 5.5.23
Platform: Other
OS/Version: Windows XP
Status: NEW
Severity: normal
Priority: P2
Component: Catalina
AssignedTo: tomcat-dev@jakarta.apache.org
ReportedBy: kgross@dor.state.wi.us
On reload of a application memory usage in the PermGen rises steadily as does
the loaded classes count. If you reload and access the application many times
and the remove the application and take a memory dump you'll that there are
still many instances of the WebappClassLoader in memory.
If you then look for what refers to these instances you find cross classloader
references. A specific case is that I find the ApplicationDispatcher class
which is loaded by StandardClassLoader has a static reference to an instance of
org.apache.commons.logging.impl.Log4JLogger that was loaded by one of the
WebappClassLoader s.
I have a very small war that I've been able to reproduce this problem with which
I'll attach. I think the important bits are that the application includes log4j
and commons-logging in the WEB-INF/lib directory and some how some catalina
classes are seeing and using this class.
I've tested this with both Sun Java Sun 1.6.0 and 1.6.0_01.
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DO NOT REPLY [Bug 42172] - Classloader leak
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kgross@dor.state.wi.us changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |REOPENED
Resolution|WONTFIX |
------- Additional Comments From kgross@dor.state.wi.us 2007-04-19 10:47 -------
I've been looking at this further and I really think there's something wrong
here. What I find wrong comes down to the fact that the variable causing the
cross reference (ApplicationDispatcher.log) is a static. How does a static
variable allow for the app server to do per webapp logging.
So I created 2 identical webapps. They have a single servlet that simply
dispatches to a JSP. I added code to the dispatch that looks at the classloader
for the servlet, request dispatcher and the log of the request dispatcher. I
then hit webapp 1 and then webapp2. I reloaded both apps and did the same again.
The code and output is included below. Basically the ApplicationDispatcher has
a log loaded by the classloader for the first webapp I hit. After a reload the
log is still the log loaded by that first webapp classloader and that
classloader is marked not started. In addition, the parent instance variable
defined in WebappClassLoader is null.
I'm not particularly knowledgeable about Tomcat yet but it would seem that using
classes loaded from one webapp while servicing the request for another webapp is
bad. And continuing to use classes loaded by a classloader that's been stopped
would seem a very bad idea.
=========== Code inserted into the servlet ===================
ServletContext sc = null;
RequestDispatcher rd = null;
sc = getServletContext();
rd = sc.getRequestDispatcher(uri);
Object log = getField(rd, "log");
ClassLoader loaderC = rd.getClass().getClassLoader();
System.out.println(loaderC);
ClassLoader loaderA = this.getClass().getClassLoader();
System.out.println(loaderA);
ClassLoader loaderB = log.getClass().getClassLoader();
System.out.println(loaderB);
System.out.println("servlet loader " + (loaderA == loaderB ? "equals" : "does
not equal") + " RequestDispatcher's log loader");
System.out.println("servlet loader " + (loaderA == loaderC ? "equals" : "does
not equal") + " RequestDispatcher loader");
System.out.println("RequestDispatcher's log loader " + (loaderB == loaderC ?
"equals" : "does not equal") + " RequestDispatcher loader");
================= Output immediately after the server comes up =======
WebappClassLoader
delegate: false
repositories:
/WEB-INF/classes/
----------> Parent Classloader:
org.apache.catalina.loader.StandardClassLoader@31f2a7
WebappClassLoader
delegate: false
repositories:
/WEB-INF/classes/
----------> Parent Classloader:
org.apache.catalina.loader.StandardClassLoader@31f2a7
servlet loader equals RequestDispatcher's log loader
servlet loader does not equal RequestDispatcher loader
RequestDispatcher's log loader does not equal RequestDispatcher loader
org.apache.catalina.loader.StandardClassLoader@5e55ab
WebappClassLoader
delegate: false
repositories:
/WEB-INF/classes/
----------> Parent Classloader:
org.apache.catalina.loader.StandardClassLoader@31f2a7
WebappClassLoader
delegate: false
repositories:
/WEB-INF/classes/
----------> Parent Classloader:
org.apache.catalina.loader.StandardClassLoader@31f2a7
servlet loader does not equal RequestDispatcher's log loader
servlet loader does not equal RequestDispatcher loader
RequestDispatcher's log loader does not equal RequestDispatcher loader
============== Output after reloading both of the applications =======
org.apache.catalina.loader.StandardClassLoader@5e55ab
WebappClassLoader
delegate: false
repositories:
/WEB-INF/classes/
----------> Parent Classloader:
org.apache.catalina.loader.StandardClassLoader@31f2a7
WebappClassLoader
delegate: false
repositories:
servlet loader does not equal RequestDispatcher's log loader
servlet loader does not equal RequestDispatcher loader
RequestDispatcher's log loader does not equal RequestDispatcher loader
org.apache.catalina.loader.StandardClassLoader@5e55ab
WebappClassLoader
delegate: false
repositories:
/WEB-INF/classes/
----------> Parent Classloader:
org.apache.catalina.loader.StandardClassLoader@31f2a7
WebappClassLoader
delegate: false
repositories:
servlet loader does not equal RequestDispatcher's log loader
servlet loader does not equal RequestDispatcher loader
RequestDispatcher's log loader does not equal RequestDispatcher loader
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DO NOT REPLY [Bug 42172] - Classloader leak
Posted by bu...@apache.org.
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------- Additional Comments From kgross@dor.state.wi.us 2007-04-19 06:50 -------
Created an attachment (id=20000)
--> (http://issues.apache.org/bugzilla/attachment.cgi?id=20000&action=view)
WAR to recreate the problem
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DO NOT REPLY [Bug 42172] - Classloader leak
Posted by bu...@apache.org.
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remm@apache.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |WONTFIX
------- Additional Comments From remm@apache.org 2007-04-19 07:06 -------
Tomcat will use the logging configuration of your web application for logging
related to the application. As a result, this may not work out that well if
you're also using reloading. In that case, I would recommend deploying your
application differently (log4j could be moved out of /WEB-INF/lib, for example).
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DO NOT REPLY [Bug 42172] - Classloader leak
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------- Additional Comments From kgross@dor.state.wi.us 2007-04-19 07:12 -------
I just want to make sure I fully understand this. If a application uses log4j
and commons logging then that application can not be redeployed without a full
stop/start of the server?
The work around you mention is moving log4j and I assume commons-logging out of
the /WEB-INF/lib. Where would be the best place to locate it then? Shared,
Common or someplace elese?
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DO NOT REPLY [Bug 42172] - Classloader leak
Posted by bu...@apache.org.
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remm@apache.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|REOPENED |RESOLVED
Resolution| |WONTFIX
------- Additional Comments From remm@apache.org 2007-04-19 13:17 -------
You have every right to find it wrong if you like, and I perfectly understand
the "issue", however what I am telling you is that this will not be fixed. As
far as I am concerned, providing the logging framework with a webapp is
possible, and can sometimes be useful, but reloading will cause problems. If you
want to use reloading, you can either stop using log4j and use java.util.logging
instead (as it is a one-per-JVM logging service, it is much more robust), or
package your application differently (log4j and the commons-logging wrapper for
log4j should be moved to a shared CL repository).
Reopening this report is not going to change this.
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DO NOT REPLY [Bug 42172] - Classloader leak
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markt@apache.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|REOPENED |RESOLVED
Resolution| |FIXED
------- Additional Comments From markt@apache.org 2007-04-22 17:36 -------
I have tracked down three places where the logger for a class was causing a
memory leak on reload with the provided test case. These have been fixed in svn
and will be included in 5.5.24 onwards.
Many thanks for the test case, it made tracking things down much easier.
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------- Additional Comments From r.weber@trustetc.com 2007-04-19 12:46 -------
This bug and 41939 may be related.
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remm@apache.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |REOPENED
Resolution|FIXED |
------- Additional Comments From remm@apache.org 2007-04-22 18:01 -------
Any component can keep a reference to a logger, so it just means the logging
setup is inapropriate with respect to the intended usage. Attemting to fix this
is not going to provide any benefit.
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markt@apache.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|REOPENED |RESOLVED
Resolution| |FIXED
------- Additional Comments From markt@apache.org 2007-05-08 17:07 -------
This has now been fixed for the provided test case but other use cases may
continue to see similar issues.
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r.weber@trustetc.com changed:
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----------------------------------------------------------------------------
CC| |r.weber@trustetc.com
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markt@apache.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |REOPENED
Resolution|WONTFIX |
------- Additional Comments From markt@apache.org 2007-04-22 17:35 -------
Re-opening to change resolution.
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