I've got two perl classes, call them A and B. A contains an array of references to B. From C (the language, not the class), I'm constructing an A, then constructing a bunch of Bs, then calling A::add( ) (written in perl, not C) to add a list of Bs. All works fine if there are fewer than 121 Bs in the list, but with more than that, something goes wrong. Depending on how I structure the code, the "something" that goes wrong can be that I get an "Attempt to free unreferenced scalar" when returning my A, or my reference to A somehow turns into &PL_sv_undef.

Some particulars: 

SV *buildA(A& a)
{
  SV *tmpSv, a_sv;
  I32 count;
  int i;
  dSP;
  ENTER;
  SAVETMPS;
  PUSHMARK;
  tmpSv = sv_2mortal(newSVpv("A", 0));
  XPUSHs(tmpSv);
  PUTBACK;
  count = call_method("new", G_SCALAR);
  // A::new {
  //   my $proto = shift;
  //   my $class = ref($proto) || $proto;
  //   my $this = { };
  //   bless($this, $class);
  //   $this->{B} = [ ];
  //   return $this;
  // }
  SPAGAIN;
  assert(1 == count);
  tmpSv = POPs;
  a_sv = newSVsv(tmpSv); // or use NEWSV/SvSetMagicSV
  PUTBACK;
  FREETMPS;
  LEAVE;

  std::vector<SV*> b_svs;
  for (i = 0; i < a.b_count; ++i) {
    tmpSv = buildB(a.b[i]);
    b_svs.push_back(tmpSv);
  }
  addBs(a_sv, b_svs);
  return a_sv;
}

[download]
buildB looks much like buildA. A::addBs looks like this: 
void
addBs(SV *a_sv, std::vector<SV*> &b_svs)
{
  SV *tmpSv;
  I32 count;
  std::vector<SV*>::iterator iter;
  dSP;
  ENTER;
  SAVETMPS;
  PUSHMARK(SP);
  tmpSv = sv_mortalcopy(a_sv);
  XPUSHs(tmpSv);
  for (iter = b_svs.begin( ); iter != b_svs.end( ); ++iter) {
    XPUSHs(sv_2mortal(*iter));
  }
  PUTBACK;
  count = call_method("add", G_VOID|G_DISCARD);
  // A::add {
  //   my $this = shift;
  //   push(@{$this->{B}}, @_);
  // }
  SPAGAIN;
  assert(0 == count);
  FREETMPS;
  LEAVE;
}

[download]
If I use newSVsv in buildA/buildB, then the SV* returned by buildA( ) seems to be &PL_sv_undef. If I use NEWSV/SvSetMagicSV, then I get the "Attempt to free unreferenced scalar" in the calling XS code: 
void get_a( )
    PPCODE:
       A a = getAFromSomewhere( );
       SV *a_sv = buildA(a);
       XPUSHs(sv_2mortal(a_sv));

[download]

In reply to Correct way to return a reference in XS/embedded perl by nikolaus

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