croaking without leaking resources

[Vaclav Barta]

Hi,

seems rather quiet in here - anybody listening? Anyway, I've written an XS
module for perl 5.8.7 (Regexp::Compare, on CPAN) using regular expressions.
It compiles them (from caller-supplied strings) with pregcomp, and I gather
the compiled regexps should be released with pregfree. That works, but I'm
concerned about invalid values. For some inputs (i.e. '[a'), pregcomp croaks
and control returns to the perl caller, which is fine, except my function
compiles *two* regexps and when the second one croaks, it doesn't get a
chance to release the first... Is there some equivalent of try/catch in XS,
or a way to register the compiled regexp as a Perl object, to be released
automatically when not needed?

Bye
Vasek

[Nick Ing-Simmons]

try/catch (i.e. eval {} in perl speak) is a little tricky to do from pure XS.
I usually call (a trivial) perl sub and use G_EVAL on the call.

So Nick C's suggestion (to another question) of using SAVEDESTRUCTOR_X
is probably the easiest.

ENTER;
SAVEDESTRUCTOR_X(your_cleanup_func, pointer_to_thing);
...
risky_stuff();
LEAVE

>
> Bye
> Vasek

[Vaclav Barta]

On Monday 01 May 2006 10:34, Nick Ing-Simmons wrote:
> > the second one croaks, it doesn't get a chance to release the first... Is
> > there some equivalent of try/catch in XS, or a way to register the
> > compiled regexp as a Perl object, to be released automatically when not
> > needed?
> try/catch (i.e. eval {} in perl speak) is a little tricky to do from pure
> XS. I usually call (a trivial) perl sub and use G_EVAL on the call.
> So Nick C's suggestion (to another question) of using SAVEDESTRUCTOR_X
> is probably the easiest.
>
> ENTER;
> SAVEDESTRUCTOR_X(your_cleanup_func, pointer_to_thing);
> ...
> risky_stuff();
> LEAVE

Yes, that's it - thanks. I suppose there's no harm in using just
SAVEDESTRUCTOR - I don't need the "context" to call pregfree (I
think :-) )...

Bye
Vasek

[Marcus Holland-Moritz]

On 2006-05-01, at 09:34:21 +0100, Nick Ing-Simmons wrote:

> Vaclav Barta <vb...@comp.cz> writes:
> >Hi,
> >
> >seems rather quiet in here - anybody listening? Anyway, I've written an XS
> >module for perl 5.8.7 (Regexp::Compare, on CPAN) using regular expressions.
> >It compiles them (from caller-supplied strings) with pregcomp, and I gather
> >the compiled regexps should be released with pregfree. That works, but I'm
> >concerned about invalid values. For some inputs (i.e. '[a'), pregcomp croaks
> >and control returns to the perl caller, which is fine, except my function
> >compiles *two* regexps and when the second one croaks, it doesn't get a
> >chance to release the first... Is there some equivalent of try/catch in XS,
> >or a way to register the compiled regexp as a Perl object, to be released
> >automatically when not needed?
>
> try/catch (i.e. eval {} in perl speak) is a little tricky to do from pure XS.
> I usually call (a trivial) perl sub and use G_EVAL on the call.

There's a way to do try/catch (under certain circumstances) in XS.
If you use a recent ppport.h, it's even portable back to perl 5.003:

XCPT_TRY_START
{
risky_stuff();
}
XCPT_TRY_END

XCPT_CATCH
{
/* cleanup things here */

XCPT_RETHROW;
}

The only limitation is that you _have to_ rethrow the exception in
the catch block, i.e. you cannot catch an exception and just ignore
it. This is documented in the perlguts and perlapi manpages.

Marcus

--
With your bare hands?!?

[Nick Ing-Simmons]

What I would do in such a case is use pointer_to_thing to the
struct regexp * to be free-d.

>
> Bye
> Vasek

[Nick Ing-Simmons]

Marcus Holland-Moritz <mhx-...@gmx.net> writes:
>>
>> try/catch (i.e. eval {} in perl speak) is a little tricky to do from pure XS.
>> I usually call (a trivial) perl sub and use G_EVAL on the call.
>
>There's a way to do try/catch (under certain circumstances) in XS.
>If you use a recent ppport.h, it's even portable back to perl 5.003:
>
> XCPT_TRY_START
> {
> risky_stuff();
> }
> XCPT_TRY_END
>
> XCPT_CATCH
> {
> /* cleanup things here */
>
> XCPT_RETHROW;
> }

Thanks, I had forgotten that had been put into ppport.h
This is almost certainly better than G_EVAL-ing a perl sub.
But this and call scheme are probably overkill if all you want
to do is cleanup on exit from scope.
I now recall that you can

callsv(an_xsub,G_EVAL)

which avoids having to have a trivial perl function.

>
>The only limitation is that you _have to_ rethrow the exception in
>the catch block, i.e. you cannot catch an exception and just ignore
>it. This is documented in the perlguts and perlapi manpages.

And as I wanted to ignore (some) cases that explains why I have
never used it and hence forgot about it.