Kerrigan Joseph created LOG4J2-406:
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Summary: JMX MBeans are not being unregistered when a tomcat web
application that uses log4j is undeployed, leading to a permgen memory leak.
Key: LOG4J2-406
URL: https://issues.apache.org/jira/browse/LOG4J2-406
Project: Log4j 2
Issue Type: Bug
Components: Core, JMX
Affects Versions: 2.0-beta9
Environment: Java 1.7.0_17-b02, tomcat 7.0.34.0, NetBeans 7.3, Windows
7 (64 bit)
Reporter: Kerrigan Joseph
When the log4j2 library is being used with a tomcat web application (included
in the web application's libraries, not in the container's libraries), tomcat
correctly discovers and initializes the Log4jServletContainerInitializer and
adds the Log4JServletContextListener as described in the
[manual|http://logging.apache.org/log4j/2.x/manual/webapp.html] (after removing
"log4j*.jar" from the jarsToSkip property as described on that page). However,
two MBeans that log4j registers (ContextSelector and StatusLogger) are never
unregistered when the web application is undeployed. This prevents the entire
web application from being garbage collected and leads to a permgen memory leak
and causes an OutOfMemoryError after a few undeploy/redeploy cycles*.
We could work around this by taking the following steps:
# Added a context parameter to the web.xml file specifying a value for the
log4jContextName parameter. This seems to prevent
java.lang.ApplicationShutdownHooks from keeping a refernce to the log4j
LoggerContext, which was part of why the memory leak was occuring**.
# In addition, took one of the following measures:
#* Added the log4j2 libraries to tomcat's classpath. Regardless of whether or
not the libraries were in the web application's classpath, this seemed to
circumvent the entire issue.
#* Disabled jmx entirely, by adding -Dlog4j.disable.jmx=true to the JVM options
for tomcat.
#* Added a custom ServletContextListener which manually unregisters all log4j
MBeans upon the destruction of the context.
Any of the steps from 2 worked equally well, but none of them worked unless we
also took step 1.
\* We used jmap and jhat to confirm that the application was not being unloaded
from memory after being undeployed, and were able to narrow the cause down to
those MBeans by tracing a reference path from the StandardClassloader through
them to the WebappClassLoader.
\** We're unsure of what role ApplicationShutdownHooks plays in this scenario,
but we observed in jhat that the reference path between log4j and
ApplicationShutdownHooks disappeared after adding the log4jContextName
parameter, and that this was necessary to stop the permgen memory leak.
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