I have the following cargo-culted code:

STATIC void croak_for_this_reason(pTHX_ ...) {
   dVAR;
   ...
   Perl_croak(aTHX_ ...);
}

croak_for_this_reason(aTHX_ ...);
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Is Perl_croak(aTHX_ ...) the same as croak(...)?

Is dVAR; needed by aTHX?

I'm using a threaded build of Perl. I thought the whole "THX mess" was to support that, yet aTHX appears to be empty (no error if I omit it). What is THX for?

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Update: I think I need this:

STATIC void croak_for_this_reason(pTHX_ ...) {
   ...
   Perl_croak(aTHX_ ...);
}

croak_for_this_reason(aTHX_ ...);
[download]

(but not dVAR;), and it which can be written as:

STATIC void croak_for_this_reason(pTHX_ ...) {
#define croak_for_this_reason(...) croak_for_this_reason(aTHX_ ...)
   ...
   croak(...);
}

croak_for_this_reason(...);
[download]