I tried to help the OP with help from perlcall 
void
registCallback(cb)
    SV* cb;
    PROTOTYPE: $
    PPCODE:
        if (callback_ref == (SV*)NULL) {
            callback_ref = newSVsv((SV*)cb);
        } else {
            SvSetSV(callback_ref, cb);
        }

[download]
I didn't realize it was WAD after getting error
Bizarre copy of CODE in entersub  (#1)
    (P) Perl detected an attempt to copy an internal value that is not
    copyable.

[download]
:)

In reply to Re^4: xs, threads and panic by Anonymous Monk
in thread xs, threads and panic by Anonymous Monk

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