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Konstantin,

On 4/29/14, 7:17 PM, Konstantin Kolinko wrote:
> 2014-04-29 12:28 GMT+04:00 Fredrik
> <fredrik.l.stigb...@sitevision.se>:
>> Hello. We're using jamm (https://github.com/jbellis/jamm) a java
>> agent for measuring object memory usage, passing the javaagent
>> argument to tomcat as 
>> "-javaagent:../../tomcat/webapps/ROOT/WEB-INF/lib/jamm-0.2.3.jar".
>>
>> 
When running 7.0.50 everything works as expected but after upgrading to
>> 7.0.52 the initialization code of the agent (premain-method)
>> isn't called anymore. Any ideas?
> 
> 
> I understand that that means that you have the same jar present in 
> both the System classloader and the Webapp classloader.
> 
> You should remove that jar from WEB-INF/lib directory of that
> webapp.
> 
> IIRC, in 7.0.50 and earlier Tomcat preferred the class from the
> system classloader (effectively ignoring the webapp's jar).
> 
> In 7.0.52 it does load the class provided by web application.

Actually, I'd like an explanation of the above. I'm not saying it's
wrong or makes no sense, but I don't quite understand how it could
interfere:

The javaagent should be loaded at JVM launch, which is before any web
applications exist, so no ClassLoader conflict should occur.

When a remote process connects to the agent, it should do so out of
context of any web application (that is, the thread that handles the
connection should not have its ClassLoader set to the
WebappClassLoader of any deployed web application), so no classes
should be loaded from the WebappClassLoader.

- -chris
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