On Sun, Sep 07, 2003 at 09:02:11AM -0700 Jan Dubois wrote:
> On Sun, 07 Sep 2003 09:49:32 +0200, Tassilo von Parseval
> <[EMAIL PROTECTED]> wrote:
> >this is the strangest thing I've ever encountered so far with XS. To me
> >it looks like a very obscure bug in perl, but hopefully it's not. The
> >Perl examples actually use autobox, but the very same behaviour shows up
> >when using a pure functional interface:
> >
> >I have a very basic C function that triggers a Perl callback:
> >
> > SV * call_Pslice (const char *func) {
> > SV *res;
> >
> > dSP;
> > ENTER;
> > SAVETMPS;
> > PUTBACK;
> >
> > (void)call_pv(func, G_SCALAR);
> > SPAGAIN;
> >
> > res = newSVsv(POPs);
> >
> > PUTBACK;
> > FREETMPS;
> > LEAVE;
> >
> > return sv_2mortal(res);
> > }
>
> You are missing a PUSHMARK(xxx) call in here. The call_pv() will pop your
> callers frame from the stack, and you caller doesn't seem to adjust for
> it.
Grrr, yes! PUSHMARK(SP) before the call fixes it. I guess since I didn't
explicitely pushed the arguments for the Perl-callback onto the stack
(and instead just left the old arguments there to pass them on), I
forgot to adjust the markstack accordingly. Thanks for spotting it, this
solves my most serious problem!
> Two more unrelated notes:
>
> 1) You call sv_2mortal() on your result without checking if the result has
> the SvREADONLY bit set. If the sub can return undef, you may be modifying
> the refcount of an immortal, which doesn't matter in most cases as it
> starts with a refcount of 2**31, but is still bad style (IMO).
The sub may return nothing actually...I omitted to handle this case.
Second thanks.
> 2) Calling call_xxx() without G_EVAL often doesn't work correctly when
> your Perl sub can die(). Maybe it is just cargo cult, but I've been
> bitten by this one too many times and now always specify G_EVAL and check
> SvTRUE(ERRSV) myself to handle exceptions myself.
That fortunately can't happen since the Perl-callback it calls is
supplied by me...it does a substitution and either returns the matched
string (matched by left side of s///) or nothing. But I have two other
places where code from the user is triggered. However, when I look at
print "foobar"->each_byte(sub { warn chr(shift), "\n"; die });
__END__
f
Died at - line 1
This seems to do the right thing. perlcall.pod says on that:
[ example ]
1. We want to be able to catch the die so we have used the G_EVAL
flag. Not specifying this flag would mean that the program
would terminate immediately at the die statement in the subroutine Sub-
tract.
I'll do a few tests and see whether not using G_EVAL can produce
inconsistent results. I guess that
if (SvTRUE(ERRSV)) croak(Nullch);
would then fix them. Thanks for warning me!
Tassilo
--
$_=q#",}])!JAPH!qq(tsuJ[{@"tnirp}3..0}_$;//::niam/s~=)]3[))_$-3(rellac(=_$({
pam{rekcahbus})(rekcah{lrePbus})(lreP{rehtonabus})!JAPH!qq(rehtona{tsuJbus#;
$_=reverse,s+(?<=sub).+q#q!'"qq.\t$&."'!#+sexisexiixesixeseg;y~\n~~dddd;eval
