[sane-devel] signal handling by libsane and backends

[Gerhard Jaeger]

On Friday 15 September 2006 16:12, Ryan Reading wrote:
> On 9/15/06, Gerhard Jaeger <gerhard at gjaeger.de> wrote:
> > On Thursday 14 September 2006 13:30, Wittawat Yamwong wrote:
> > > Hi,
> > >
> > > On Thursday 14 September 2006 09:09, Gerhard Jaeger wrote:
> > > > On Tuesday 12 September 2006 04:02, Ryan Reading wrote:
> > > > > The sane library and/or its backends don't seem to "clean up" after
> > > > > themselves by restoring signal handlers and/or signal masks.
> > > > > [...]
> > > >
> > > > And yes, I think you are right. Grep for sigaction or signal function
> > > > calls within the backend directory and you'll see, that no backend
> > > > saves the old sigmasks or handlers for restoring.
> > >
> > > I think, it is OK if the backend modifies sigmasks and/or installs
> > > signal handlers in the _child_ process but doesn't restore them. On the
> > > other hand, as Ryan mentioned, it will probably cause problems if you
> > > do it in the parent process and do not take special care of old
> > > sigmasks and signal handlers.
> > >
> > > > Even sanei_thread does not restore the tweaked masks/handlers.
> > > > Workaround could be to get the settings before calling any sane
> > > > function and to do the restore stuff on your own.
> > >
> > > This should be documented somewhere, maybe in PROBLEMS?
> >
> > Nope, I think it should be fixed...
> > I digged a little deeper to sanei_thread and the only points, where
> > we fiddle with signals is
> > SIGPIPE and
> > SIGUSR2 (only for __APPLE__ && __MACH__)
> >
> > SIGPIPE will be restored
> > SIGUSR2 not, which is IMHO not critical
> >
> > So the point to fix are inside the backends. If someone could
> > provide a testcase, this could be easily fixed.
> >
> > Gerhard
> >
>
> Thanks for the quick replies.  (My bad on the HTML... I have no idea
> why I was even using hotmail).
>
> I agree that the handlers in the child process are not a big deal.
> The particular backend that I was using was "plustek".  It
> specifically sets a SIGCHLD handler.  I think SIGALRM is affected in
> other backends.  Anyway, I could put together a test case that
> exhibits the problem if needed.  In what form should a test case be in
> to most useful?  Where could I look for an example?  I didn't see any
> code in the "testsuite" dir in the source tree.
>

The plustek backend, that's what I expected ;)
I'm the maintainer of this piece of code, so when returning from
holiday, I'll try to fix that issue.

Gerhard