Debug-Hints with Tomcat

[Benedikt Rothe]

Thanks Umberto! Good hint. In this context I found something.

Since this kind of problem may occure to others to, I'll briefly 
summarize the steps I go:

a) In map.h include somewhere the line
#include <mcheck.h>

b) Compile Mapserver with debug-option:
./configure <flags>  --enable-debug
make

c) Before starting tomcat set the environmentvariable  MALLOC_TRACE
to the name of a logfile.
export MALLOC_TRACE=/opt/jakarta-tomcat-4.1.31/logs/malloctrace

The tracefile will contains information about calls to "malloc" and 
"free":
   - Function called malloc/free 
   - address of allocated/freed memory

By this file one can look for the "pairs". 

I'll still have to test in in practice. But I'm hopefull, that this will 
help to 
narrow the problem down.

Benedikt Rothe


Umberto Nicoletti <umberto.nicoletti at gmail.com> schrieb am 02.11.2005 
12:29:05:

> Newer glibc have internal checks that are probably turned on by
> default on some distros.
> Try to play with the MALLOC_CHECK_ variable and read this (it is about
> fedora core, but should apply to suse too):
> 
>     glibc
>       The version of glibc provided with Fedora Core 3 performs
>       additional internal sanity checks to prevent and detect data
>       corruption as early as possible. By default, should corruption
>       be detected, a message similar to the following will be displayed
>       on standard error (or logged via syslog if stderr is not open):
> 
>       *** glibc detected *** double free or corruption: 0x0937d008 ***
> 
>       By default, the program that generated this error will also be
>       killed; however, this (and whether or not an error message is
>       generated) can be controlled via the MALLOC_CHECK_ environment
>       variable. The following settings are supported:
> 
>             0 -- Do not generate an error message, and do not kill the 
program
>             1 -- Generate an error message, but do not kill the program
>             2 -- Do not generate an error message, but kill the program
>             3 -- Generate an error message and kill the program
> 
>       Note
> 
>       If MALLOC_CHECK_ is explicitly set a value other than 0, this
>       causes glibc to perform more tests that are more extensive than
>       the default, and may impact performance.
> 
>       Should you have a program from a third party ISV that triggers
>       these corruption checks and displays a message, you should
>       file a defect report with the application's vendor, since this
>       indicates a serious bug.
> 
> Best regards,
> Umberto
> 
> On 11/2/05, Benedikt Rothe <umn-ms at hydrotec.de> wrote:
> >
> > Dear Mapserver-Users
> >
> > We developed a Tomcat/Mapserver-Site using Mapscript on
> > Linux/SUSE 9.3.
> >
> > Many things run fine. On a test-machine we made successfully
> > some stress-testing and Tomcat runs for weeks.
> >
> > Unfortunately Tomcat crashes on the customers production-machine
> > approximately once a day. It runs for several hours,
> > passes stress-tests successfully but crashes unpredictable after
> > 12-20hours.
> >
> > The crash occurs in Mapserver-Code. Message in the Tomcat-log
> > is
> > *** glibc detected *** double free or corruption (top): 0x0xf99950"
> >
> > Question: Can I do something to make this error-message more helpful?
> > I'd like to have the stack and the line-numbers in the sourcecode.
> > (I mean the C-stack and C-linenumber and not the Java-Stack...)
> >
> > I looked through the gcc-man-page, but I coudn't find anything 
helpful.
> >
> > Thanks
> > Benedikt Rothe
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