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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: How do you catch these exceptions
Date Sat, 01 Nov 2014 23:13:27 GMT
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Konstantin,

On 11/1/14 8:59 AM, Konstantin Kolinko wrote:
> 2014-11-01 3:57 GMT+03:00 Campbell, Lance <lance@illinois.edu>:
>> 
>> Tomcat 7.0.56
>> 
>> Java 7.0_72
>> 
>> 
>> 
>> I received the below Tomcat error messages in a web application.
>> Is there a way for me to catch these exceptions so that I can
>> then either execute Java code or trigger a Linux shell script?
>> 
>> 
>> 
>> Oct 31, 2014 7:38:25 PM
>> org.apache.tomcat.util.net.NioEndpoint$SocketProcessor doRun
>> 
>> SEVERE:
>> 
>> java.lang.OutOfMemoryError: Java heap space
>> 
>> 
>> 
>> Oct 31, 2014 7:38:46 PM
>> org.apache.tomcat.util.net.NioEndpoint$Acceptor run
>> 
>> SEVERE:
>> 
>> java.lang.OutOfMemoryError: Java heap space
>> 
>> 
>> 
>> Oct 31, 2014 7:38:49 PM
>> org.apache.tomcat.util.net.NioEndpoint$Poller run
>> 
>> 
>> Thanks,
> 
> There is a family of options such as -XX:OnOutOfMemoryError, 
> -XX:+HeapDumpOnOutOfMemoryError in Oracle Java. The first one is
> used to launch an external script in case of OOM.
> 
> Doing anything from Java rarely works in case of an OOM error, 
> especially a "PermGen" OOM. (You have a bit more luck with your
> "Java heap space" one).
> 
> See http://markmail.org/message/rr26epg4oap4syus "Notification
> strategy for OutOfMemoryError" thread from about a year ago.

+1

My experience is that, of the options available, the
- -XX:OnOutOfMemoryError option is the most reliable.

However.

Since I've been using that technique, there have been plenty of times
where I've found an OOME condition (shown in catalina.out, for
instance) and the JVM has actually not executed my external script.

YMMV

I've also implemented a Filter that catches OutOfMemoryError and
attempts to log the condition. I have very little data about how often
it actually runs, but it definitely does run sometimes: it helped us
find a runaway-search bug that happened in a mundane part of our web
application, because we were able to see the query string being sent
by the remote user.

The Filter basically just wraps a try/catch block around
chain.doFilter(...) with this as the exception handler:

        catch (OutOfMemoryError oome)
        {
            logger.error("Detected OutOfMemory condition during request");
            logger.error("Here are some request details:");
            logger.error("Next line will contain the current request's
URI");
            logger.error(request.getRequestURI());
            logger.error("Next line will contain the current request's
query string (if any):");
            logger.error(request.getQueryString());
            logger.error("Next line will contain the original
request's URI (essentially what the client actually requested)");

logger.error(request.getAttribute("javax.servlet.forward.request_uri"));
            logger.error("Next line will contain the original
request's query string (if any):");

logger.error(request.getAttribute("javax.servlet.forward.query_string"));
            logger.error("Finally, the current user (if any):");
            logger.error((null != request.getSession(false)
                    && null !=
request.getSession(false).getAttribute("user")
                    ? request.getSession(false).getAttribute("user")
                            : "no current user"));

            _application.setAttribute(OOME_KEY,  Boolean.TRUE);

            throw oome;
        }

Note that, other that whatever overhead the logger itself adds, there
are no memory allocations that occur in the exception handler itself.

Hope that helps,
- -chris
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