Basically, I am trying to do an embedded Perl application. In my design I wanted to invoke a set of functions with different parameter lists for each function, and also have a known set of global variables available within each function.

I have gotten the parameters passed to the functions working. However, I am having difficulty creating Perl global variables from within the C code. There is no documentation on PerlDocs on how to create global variables, and the book "Advanced Perl Programming" talks about global variables, but has no working examples. I had the idea that I would include a Perl module in the script, and create the global variables in the Perl module's stash.

If I use perl_parse() and perl_run() to get the module loaded, I can look at existing global variables in the module. I used gv_stashpv() to get a handle to the loaded module's stash. Once I have the handle to the module's stash, I can use hv_iterinit() and hv_iternext() to walk the stash's list of functions and variables present in the module.

Doing a detailed examination of the SV's in this stash, I have found that a valid global variable in a stash is a complex chain of records in the form:

An SV points to an XPVGV which points to a GP which has a pointer in the specific slot for the variable type. I have also found that the GP points back to the originating SV in a circular reference.

I cannot find an API to recreate this complex chain. I have found that the following code: 

    sv = newSV( 0 );
    SvUPGRADE( sv, SVt_PVGV );

[download]

creates the SV which points to an XPVGV. I cannot find an API call to create and link the GP to the end of this chain. I tried the following code: 

    GvGP(sv)         = Perl_calloc( 1, sizeof(GP) );
    GvHV(sv)         = hash;            // A hash I want to be global
    GvEGV(sv)        = (GV *) sv;
    GvREFCNT(sv)     = 1;

    hv_store( hStash, "TestGlobal", strlen("TestGlobal"), sv, 0 );

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But this code causes the Perl engine to trap after the call_pv() function returns. This makes me believe that I have corruped the heap and the garbage collector dies when the mortal stack variables are destroyed.

So, how do I create a proper glob variable in a module stash in a polite and proper method? I am close, but I am sure I am missing a small detail that is corruption the heap. Anyone have some advice?

(I can provide a much more detailed example if needed.)

Thank you in advance.

In reply to Embedded Perl Global Variables by Anonymous Monk

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