[GRASS-user] Label crash

[Glynn Clements]

Markus Neteler wrote:

> > If I generate a label:
> > v.label map=Labels column=stuff font=/usr/X11R6/lib/X11/fonts/TTF/Vera.ttf
> > then it displays fine in the gui.  But if I try to use other monitors from
> > the command line I consistently get a crash.  For example:
> >
> > d.mon start=PS
> > d.labels labels=Labels
> 
> I have tried with Spearfish, GRASS 6.4.0RC4, Linux 64bit:
> 
> v.label  map=roads colum=label font=/usr/share/fonts/TTF/Vera.ttf
> d.mon start=PS
> d.labels labels=roads
> d.mon stop=PS
> kghostview map.ps
> 
> No problem, looks fine.
> It seems to be Mac specific.
> 
> > And I get the following repeated a whole bunch of times:
> >
> > The process has forked and you cannot use this CoreFoundation functionality
> > safely. You MUST exec().
> > Break on
> > __THE_PROCESS_HAS_FORKED_AND_YOU_CANNOT_USE_THIS_COREFOUNDATION_FUNCTIONALITY___YOU_MUST_EXEC__()
> > to debug.
> >
> > The same thing happens if I use d.mon start=PNG.
> 
> could fork() in
>  lib/driver/main.c
> be the problem?

Yes. It's basically a symptom of "MacOSX is sort of Unix, but not
quite".

A similar issue affects libW11 on Cygwin. There, mon.start runs the
driver in the background (spawnl(_P_DETACH, ...)) with argv[2] = "-",
which prevents it from fork()ing.

Something similar could be done for MacOSX. However, this isn't
robust, as it relies upon mon.select retrying upon failure. If the
driver takes too long to start, mon.select will fail.

-- 
Glynn Clements <glynn at gclements.plus.com>