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All,
On 5/31/13 11:39 AM, Christopher Schultz wrote:
> - Using MySQL Connector/J 5.1.24 (important later) - Not running
> under a SecurityManager - <Context> has no "clearReferences...*"
> attributes set (all default to "false" save for
> HttpClientKeepAlive)
>
> [...]
>
> WebappClassLoader ^- classloader of java.security.ProtectionDomain
> ^- [7] of java.security.ProtectionDomain[8] ^- context of
> java.security.AccessControlContext ^- inheritedAccessControlContext
> of com.mysql.jdbc.AbandonedConnectionCleanupThread
It seems that the AbandonedConnectionCleanupThread itself is not to
blame: it hardly has any code in it at all, other than this
astoundingly ineffective attempt to avoid ClassLoader leakage in the
run() method:
threadRef.setContextClassLoader(null);
Connector/J 5.1.25 (one patch-version after the one I'm currently
running has removed that line, so there's now a direct link from the
thread to the WebappClassLoader. Brilliant.)
Anyhow, everything crystallized in Thread.init(), called from
Thread.<init>, so is happens even before MySQL's thread had a chance
to do anything (such as change the context ClassLoader).
The context class loader needs to be set /before/ the Thread is
created, and that happens in MySQL's JDBC driver's static initializer,
like this:
static {
AbandonedConnectionCleanupThread referenceThread = new
AbandonedConnectionCleanupThread();
referenceThread.setDaemon(true);
referenceThread.start();
}
*sigh*
I've commented on the bug... we'll see if anything else happens.
It appears that using the JreMemoryLeakPreventionListener's
classesToInitialize set to "com.mysql.jdbc.NonRegisteringDriver" seems
to do the trick: clean reloads again.
/me sighs satisfactorily
Then again, using classesToInitialize is a total hack.
Would it be reasonable to have the context ClassLoader of the thread
Tomcat is using to create the JNDI DataSource be temporarily set (if
necessary) to the ClassLoader that actually loaded the Driver itself?
That way, if the driver is loaded from WEB-INF/lib, then these kinds
of threads will get the WebappClassLoader as their context ClassLoader
(which I believe is appropriate), and those loaded from
CATALINA_BASE/lib will get the container's ClassLoader (which I
believe if appropriate, since the driver shouldn't be loading
webapp-specific classes).
- -chris
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