Re^2: what definition of Istack_sp

[xiaoyafeng]

Thanks！ I've found statement in intrpvar.h: PERLVAR(I, stack_sp, SV **) /* top of the stack */ and in perl.h:

#  define PERLVAR(prefix,var,type) type prefix##var;

/* 'var' is an array of length 'n' */
#  define PERLVARA(prefix,var,n,type) type prefix##var[n];

/* initialize 'var' to init' */
#  define PERLVARI(prefix,var,type,init) type prefix##var;

/* like PERLVARI, but make 'var' a const */
#  define PERLVARIC(prefix,var,type,init) type prefix##var;

struct interpreter {
#  include "intrpvar.h" 
};

So perl use PERLVAR to define perlinterpreter struct, it's strange to me, why is it not define perlinterpreter structure directly in perl.h? Please enlighten me.

[dave_the_m]

The perl binary has multiple ways in which it can be built. The simplest (and original) model just defines PL_stack_sp directly as a global variable. But when built with MULTIPLICITY (when for example building a threaded perl), then multiple interpreters are allowed, and (within the core), PL_stack_sp is defined as my_perl->Ispack_sp.

However in XS code (rather than in the core), it's more complex. At one point PL_stack_sp was defined as a function call, which would shield the XS code from changes in the interpreter struct layout across differing perl versions - so XS modules wouldn't have be to recompiled for each new perl release. However, this slowed XS code down a lot, and there were other things which also broke binary compatibility, so that was ditched and we just changed the binary guarantee to apply only across minor releases.

Dave.

[xiaoyafeng]

Thanks for your detailed answer! By the way, as your replied on this , 5.30 will add named parameter. I'm curious if it would affect current mechanism of argument stack which you mentioned above?

[dave_the_m]

Thanks for your detailed answer! By the way, as your replied on this , 5.30 will add named parameter. I'm curious if it would affect current mechanism of argument stack which you mentioned above?

That's no longer likely to happen for 5.30: I ran out of time. Named sub parameters will only affect the sub itself, not the caller; and named args will only apply to perl subs, not to XS subs.

Dave.