Seeking (Mod)Perl Wisdom

[Torsten Foertsch <to...@gmx.net>]

Hi,

the a pointer to current interpreter is somehow written to the Perl 
interpreter itself by this macro:

#ifndef HvPMROOT
# if MP_PERL_VERSION_AT_LEAST(5, 9, 5)
#define MP_THX_INTERP_SET(thx, interp)                          \
    ((XPVMG*)SvANY(*Perl_Imodglobal_ptr(thx)))->xmg_u.xmg_magic = 
(MAGIC*)interp
# else
#define MP_THX_INTERP_SET(thx, interp)                          \
    ((XPVMG*)SvANY(*Perl_Imodglobal_ptr(thx)))->xmg_magic = (MAGIC*)interp
# endif
#else
#define MP_THX_INTERP_SET(thx, interp)                          \
    HvPMROOT(*Perl_Imodglobal_ptr(thx)) = (PMOP*)interp
#endif

What is HvPMROOT and what is Perl_Imodglobal_ptr? Are these normal Perl 
variables that can also be accessed from Perl level? If not why are here 
special variables used? Can that not be something like 
$Modperl::CurrentInterpreter or so?

Torsten

Re: Seeking (Mod)Perl Wisdom

["Philippe M. Chiasson" <go...@ectoplasm.org>]

Torsten Foertsch wrote:
> Hi,
> 
> the a pointer to current interpreter is somehow written to the Perl 
> interpreter itself by this macro:
> 
> #ifndef HvPMROOT
> # if MP_PERL_VERSION_AT_LEAST(5, 9, 5)
> #define MP_THX_INTERP_SET(thx, interp)                          \
>     ((XPVMG*)SvANY(*Perl_Imodglobal_ptr(thx)))->xmg_u.xmg_magic = 
> (MAGIC*)interp
> # else
> #define MP_THX_INTERP_SET(thx, interp)                          \
>     ((XPVMG*)SvANY(*Perl_Imodglobal_ptr(thx)))->xmg_magic = (MAGIC*)interp
> # endif
> #else
> #define MP_THX_INTERP_SET(thx, interp)                          \
>     HvPMROOT(*Perl_Imodglobal_ptr(thx)) = (PMOP*)interp
> #endif

That's right, its so we can get to the modperl_interp_t from a good perl THX.
It's seriously a hack, but it does the job quite nicely, and there doesn't
seem to be a much better way to do it. It just uses an unused magic field
to stash that pointer.

> What is HvPMROOT and what is Perl_Imodglobal_ptr?

Not even sure what HvPMROOT was, but it was just a semi-arbitrairly chosen
field of the modglobal HV that wasn't likely to be used, ever.

> Are these normal Perl 
> variables that can also be accessed from Perl level?

Nope, they are deep inside the guts of Perl. modglobal is documented somewhere
in perlguts, and it's just a general purpose HV* in the interp structure for
this kind of magic.

> If not why are here 
> special variables used?

Basic idea if I remember correctly was to be able to get back to the modperl_interp_t
from a Perl interp. To make matters trickier, you need to be able to retrieve it out
of there without actually entering Perl-land. That's why instead of sticking it
in the modglobal hash, it's hagning off one of it's unused struct member.

> Can that not be something like 
> $Modperl::CurrentInterpreter or so?

Seems the original idea was to avoid going thru the perl runtime to figure it out.

Hope this helps a little.

------------------------------------------------------------------------
Philippe M. Chiasson     GPG: F9BFE0C2480E7680 1AE53631CB32A107 88C3A5A5
http://gozer.ectoplasm.org/       m/gozer\@(apache|cpan|ectoplasm)\.org/