Jim Jim - 4 months ago 28
Linux Question

Tomcat doesn't stop. How can I debug this?

I have a

Tomcat 7
running in Linux that I start via
$CATALINA_HOME/bin/startup.sh
and shutdown via
$CATALINA_HOME/bin/shutdown.sh


from
/etc/init.d


All is ok except 1 problem. Sometimes tomcat does not stop.

Although I stop it and I see in catalina.out logs that is going down, if I do
ps -ef
I can still see the process running.

What could be the problem? How can I debug this? My feeling is, that this is related to threads.

So the parts that are suspicious are the following:

1) I use Log4j's LogManager to detect if the log4j configuration has been changed, but I do
Log4jManager.shutdown
on a
contextDestroyed
ServletContextListener


2) I use
H2
database and I see on shutdown:


SEVERE: The web application [/MyApplication] appears to have started a

thread named [H2 Log Writer MYAPPLICATION] but has failed to stop it.

This is very likely to create a memory leak

SEVERE: The web application [/MyApplication] appears to have started a

thread named [H2 File Lock Watchdog

/opt/myOrg/tomcat/webapps/MyApplication/db/myDatabase.lock.db] but has

failed to stop it. This is very likely to create a memory leak. Apr 2,

2012 9:08:08 AM org.apache.catalina.loader.WebappClassLoader

clearReferencesThreads SEVERE: The web application [/MyApplication]

appears to have started a thread named [FileWatchdog] but has failed

to stop it. This is very likely to create a memory leak.


Any help please? How can I detect the problem here?

UPDATE:

I did a
kill -3
as suggested by @daveb, and in the catalina.out I see:


JVMDUMP006I Processing dump event "user", detail "" - please wait.
JVMDUMP032I JVM requested Java dump using
'/etc/init.d/javacore.20120402.093922.2568.0001.txt' in response to an
event JVMDUMP010I Java dump written to
/etc/init.d/javacore.20120402.093922.2568.0001.txt JVMDUMP013I
Processed dump event "user", detail "".


There is a javacore in
/etc/init.d
but I don't know how to process it. I.e. what parts should I investigate

Answer

If the web application is stopped, all connections to the database should be closed as well. If you don't have a list of connections, then execute the SQL statement "shutdown" (this only works for the H2 and HSQLDB databases).

If you have a registered a Servlet, you can do that in the Servlet.destroy() method.

If you have registered a ServletContextListener, you can execute the "shutdown" statement in the ServletContextListener.contextDestroyed(ServletContextEvent servletContextEvent) method. This is what org.h2.server.web.DbStarter ServletContextListener does (the one that is included in the H2 database).

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