[Mapserver-users] mod_perl segfaults

[Lowell Filak]

The following message was sent by Robert Marcus Evans
<rob at ert.dyndns.org> on Tue, 15 Jun 2004 10:24:56 -0400.

> Actually, we're using mod_perl/HTML::Mason in one place, and straight
cgi's
> in another. The CGI's don't ever seem to crash, whereas the mason is
> unstable. I don't think it would be a threading issue, as I create a
new map
> object for each request. However, it would be possible for multiple
> simultaneous map objects to exist for the same base file. Furthermore,
I use
> the static .map file as a base, and draw different dynamic objects on top,
> depending on the request. I don't explicitly kill the map objects (is
there
> some kind of locking mechanism?), but then they're in a lexical scope and
> should be garbage collected. You guys seem to be suggesting that if I
used a
> static map object for each apache process, the problem would still exist.
> Anyone have any other ideas?
> 
> -rob
> 
> Lowell Filak wrote this on Tue, Jun 15, 2004 at 09:47:38AM -0400:
> > The following message was sent by covad at ert.dyndns.org on Mon, 14 Jun
> > 2004 15:30:43 -0400.
> > 
> > > I'm getting errors like the following:
> > > 
> > > [Mon Jun 14 14:22:49 2004] [notice] child pid 19412 exit signal
> > Segmentation fault (11)
> > > 
> > > in my apache error log, but only intermittently. The site is
usable, but
> > > craps out ~25% of the time.
> > > 
> > > I'm running perl mapscript 4.2.0, apache 1.3.31, and mod_perl 1.29.
> > > 
> > > Has anyone else seen behavior like this?
> > > 
> > > Would rolling back to mapscript 4.0 help?
> > > 
> > > Thanks,
> > > 
> > > -rob
> > > 
> > 
> > Rob
> > 
> > As Sean mentioned before - it is probably due to multiple requests into
> > the same map/mapObj.
> > Starting in 4.2 it should be safe to clone the map to avoid this but it
> > does require more testing then what has been done.
> > If that doesn't work I know that GOMOOS (currently very busy so I'm not
> > sure they will reply) currently uses mod_perl but opens a new map for
> > each request to ensure that two requests do not conflict.
> > 
> > Lowell
> 

Rob

Until I have a chance to switch our server to mod_perl I can't reproduce
the issue but I meant to suggest that you Do use a static map object for
each request to try and eliminate the problem.
Dynamic objects being drawn via MapScript only change the map object and
not the map file so it sounds like your expecting the map object to not
be shared between requests but in fact it is.?
You do not need to explicitly kill map objects and as long as seperate
requests are not sharing the same map object the process of 'reading'
the same static map file is read-only so no locking should be
required... unless your doing a saveMapContext.?

Lowell