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SubjectRe: pthreads & fork & execve
Hi!

I tracked this down to a corrupt jumptable somewhere in the pthreads
part of the libc (didnt have the source handy at that time, though). So
I think this is a libc bug (version does not matter) - I even did a
followup to a similar bug in the libc gnats database (I think I should
have opened a new one, though...). But I failed to construct a "simple"
testcase showing the bug (We use rather large amount of threads and
in one or two doing popen() calls - or handcrafted fork() && execv(),
the SIGSEGV is during fork()).

I stopped trying to find out what is going on as this feature is not
essential (but maybe useful in the future). So I suggest you build a
libc from source with debugging on and trace it down to the actual
libc problem - or better try to isolate a simple testcase.

I like to hear from the results :)

Richard.

On Fri, 30 Mar 2001, Dennis Noordsij wrote:

> Hi,
>
> I have question regarding use of pthreads, forks and execve's which appears
> to not work very well :-) First let me explain the reasoning though
>
> We have an app that launches a few other apps and keeps track of their
> status, resource consumption etc. If one of the apps crashes, it is restarted
> according to certain parameters.
>
> The app uses pthreads, and it's method of (re)starting an application is
> forking and calling execve.
>
> It works fine for all-but-one other app, which core dumps when started this
> way (from the commandline it works fine) and the core only traces back to
> int main(int argc, char **argv). It uses both pthreads and -ldl for plugin
> handling.
>
> We have tried changing the linking order (i.e. -ldl -lpthread, -lpthread,
> -ldl, etc), and even execv'ing a shell script that starts a shell script that
> starts the app - result is the same, instant core without even running.
>
> I can see who forks together with threads and execve's are a messy
> combination, and a better solution altogether to our approach is appreciated
> just as much as a way to make the current solution work :-)
>
> We have tested both kernels 2.4.2 and 2.2.18.
>
> We have tried on different systems, different hardware and slightly different
> distributions (debian potato, unstable, etc).
>
> To sum up: using a pthreaded app to launch another pthreaded app by means of
> forking and exec(ve)'ng makes the second app core immediately, (at entering
> main). What to do?
>
> Kind regards, and thanks for any help
> Dennis Noordsij
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--
Richard Guenther <richard.guenther@uni-tuebingen.de>
WWW: http://www.tat.physik.uni-tuebingen.de/~rguenth/
The GLAME Project: http://www.glame.de/

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