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All,
My primary webapp (and ClassLoader) used to unload cleanly but now I
get WebappClassLoaders still stuck in memory after a reload. I'm
having a little trouble figuring out exactly what is holding onto
references. Here's what I know:
- - Tomcat 7.0.40
- - Running Sun/Oracle Java 1.6.0_26 64-bit Server JVM
- - Running on Linux 2.6.32 kernel
- - Using MySQL Connector/J 5.1.24 (important later)
- - Not running under a SecurityManager
- - JreMemoryLeakPreventionListener is enabled
- - <Context> has no "clearReferences...*" attributes set (all default
to "false" save for HttpClientKeepAlive)
I took a heap dump, and I can see that I have a WebappClassLoader
pinned in memory, "started=false", etc.
When looking at the GC roots, I can see the following references to
the WebappClassLoader:
WebappClassLoader
^- classloader of java.security.ProtectionDomain
^- [7] of java.security.ProtectionDomain[8]
^- context of java.security.AccessControlContext
^- inheritedAccessControlContext of
com.mysql.jdbc.AbandonedConnectionCleanupThread
There are a few other roots, but they are either (almost) identical to
the above or similar enough to the above that I figure they are pretty
much the same: this Connector/J thread has an indirect reference to my
WebappClassLoader for some reason.
Here's what I know about that thread:
- - It's class's ClassLoader is an o.a.c.loader.StandardClassLoader (yay!)
- - The Thread's Class's ProtectionDomain's ClasSLoader is
StandardClassLoader (yay!)
- - I'm not sure what that Thread's current context class loader is (any
idea how to find out? Browsing the object's members isn't leading me
anywhere)
- - The thread is running.
AbandonedConnectionCleanupThread has a member called
inheritedAccessControlContext which is a wrapper around
ProtectionDomain[]. Some elements in that array have a ClassLoader of
my WebappClassLoader, while others have StandardClassLoader and still
others have the JVM's application ClassLoader (the one once-removed
from boot, Chuck ;).
So, it looks like the ProtectionDomain objects themselves are what are
trapping me, here.
I'm not an expert at the internals of Java's security infrastructure,
nor have I dived into the Connector/J code (yet). I was wondering if
anyone had any guidance for me before I proceed.
(There is an updated 5.1.25 Connector/J driver that has a note in the
ChangeLog about ClassLoader references specifically-related to Tomcat.
I'll try with the latest -- which is likely to have a regression in it
because of the stupid fix to http://bugs.mysql.com/bug.php?id=68556 --
and see what the differences are).
At any rate, I'm curious as to where the ProtectionDomain objects are
actually created.
Thanks,
- -chris
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