Help with XS and anonymous arrays

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I'm creating an OO module in XS and have encountered a problem when one of the parameters is an array reference. If the function is passed a reference is to a named array (\@array) it works, but when passed a reference to an anonymous array ([@array\), it mysteriously fails. When I run this test:

my @array = '1' .. '3';
my $test = Test->new([@array]) :
print "Ref: ", ref $g->avref, "\n";
use Devel::Peek;
Dump($g->avref);
[download]

I get the following:

SvTYPE: 10
Ref: REF
Attempt to free unreferenced scalar: SV 0x1801464, Perl interpreter: 0
+x1800400 at a line 16.
SV = RV(0x1811aa4) at 0x180147c
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x1801464
  SV = PV(0x1801684) at 0x1801464
    REFCNT = 1
    FLAGS = (POK,pPOK)
    PV = 0x301f90 "(0x1811aa4) at 0x180147c\n  REFCNT = 1\n  FLAGS = (
+TEMP,ROK)"\0
    CUR = 58
    LEN = 59
[download]

Whereas when I replace \@array for [@array] I get the expected:

SvTYPE: 10
Ref: ARRAY
SV = RV(0x1811aa4) at 0x1801464
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x180c2c0
  SV = PVAV(0x180283c) at 0x180c2c0
    REFCNT = 2
    FLAGS = (PADBUSY,PADMY)
    IV = 0
    NV = 0
    ARRAY = 0x327a10
    FILL = 2
    MAX = 3
    ARYLEN = 0x0
    FLAGS = (REAL)
    Elt No. 0
    SV = IV(0x1826870) at 0x1801380
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 1
    Elt No. 1
    SV = IV(0x1826874) at 0x1801434
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 2
    Elt No. 2
    SV = IV(0x1826878) at 0x180144c
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 3
[download]

I've read perlxs, perguts, perlapi, "Extending and Embedding Perl" and googled my brains out, but can't find anything relevant. This is the contents of Test.xs:

#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "ppport.h"

typedef struct {
  AV  *avref;
} test_t;

typedef test_t *Test;

MODULE = Test  PACKAGE = Test

Test
new (char *class, SV *avref)
PROTOTYPE: $\@
CODE:
{
    IV i;
    test_t *self;
    New(0, self, 1, test_t);
    printf("SvTYPE: %d\n", SvTYPE(SvRV(avref)));
    self-&gt;avref = (AV*)SvRV(avref);
    RETVAL = self;
}
OUTPUT:
    RETVAL

AV *
avref (Test self, AV *avref=Nullav)
PROTOTYPE: $;\@
CODE:
{
    if (items == 2)
      self-&gt;avref = avref;
    RETVAL = self-&gt;avref;
}
OUTPUT:
    RETVAL
[download]

and the typemap is: Test T_PTROBJ

Comment on Help with XS and anonymous arrays Select or Download Code

Replies are listed 'Best First'.
Re: Help with XS and anonymous arrays by rafl (Friar) on Mar 28, 2006 at 23:22 UTC
Either make a copy of the array that was passed to new or simply increase its reference count. Otherwise perl tries to free it, as you see. That doesn't happen if you pass a named reference because the array is still in the same scope and won't get destroyed therefor. For example it should also work with with an anonymous reference if you store it in another lexical variable: `my @array = 1 .. 3; my $ref = [@array] Test->new($ref);` [download] Cheers, Flo	[reply] [d/l]
Re^2: Help with XS and anonymous arrays by Anonymous Monk on Mar 29, 2006 at 00:17 UTC
Thanks! That did the trick. I added: `if (SvREFCNT(avref) == 0) SvREFCNT_inc(avref);` [download]	[reply] [d/l]
Re^3: Help with XS and anonymous arrays by rafl (Friar) on Mar 29, 2006 at 00:26 UTC
That's wrong as well. Don't conditionally increment the reference count. Incement it when you create a new reference to it and decrement it when you're not referencing to it anymore. Cheers, Flo	[reply]