Thanks tye - this is extremely helpful. So I just want to make sure that I understood properly what you recommend to do. Does the following code give a decent example of how to push an array ref and a hash ref onto the stack?

    dSP;
    ENTER;
    SAVETMPS;
    PUSHMARK(SP);

    AV *arr = newAV();
    av_push( arr, newSVpv("string", 0));
    XPUSHs(sv_2mortal(newRV_noinc((SV *)arr)));

    HV *hash = newHV();
    SV *type = newSVpv("string", 0);
    hv_store( hash, "type", strlen("type"), type, 0);
    XPUSHs(sv_2mortal(newRV_noinc((SV *)hash)));

    PUTBACK;
    call_sv(sv_2mortal(newSVpv("TestPM::test_leak", 0)), G_SCALAR);
    SPAGAIN;
    SV *retval = POPs;
    PUTBACK;
    FREETMPS;
    LEAVE;
[download]

I'd really appreciate it if you could validate this approach, which is my understanding of what you explained above.

Regarding your other questions:

1. The printf/exit was just an example - my real code is actually throwing an exception there. Actually, it's also doing a FREETMPS/LEAVE - is that the right thing to do if I'm expecting the process to stay alive, and I want everything cleaned up? Will that work okay with the non-mortal approach you're advocating?
2. I was calling SvREFCNT_inc() since it seemed to me from the hv_store() docs that I needed to. But you're saying that I don't, right? I have to say that I'm still left feeling like the above code might work, but isn't really handling refcounts correctly. But I trust you more than I trust my gut feelings here...
3. call_sv() was also just an example - my real code is calling call_method().

So wouldn't it be better if I do mortalize everything, and just SvREFCNT_inc whenever I either av_push() or hv_store() the SV, as well as using newRV_inc()? Will that not work and be correct?

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