in reply to Re: odd line in windows
in thread odd line in windows

new function does avoid the warning, but what does AV* mean in perl? a SV* are able to be a reference of array other than a AV*. though I'm still digging how this warning come, I insist using SV* as returning.


I am trying to improve my English skills, if you see a mistake please feel free to reply or /msg me a correction

Replies are listed 'Best First'.
Re^3: odd line in windows
by ikegami (Patriarch) on Sep 08, 2011 at 09:26 UTC

    The typemap automatically creates a reference to it and returns the reference. It's refcount is off by one, though. 

    use strict;
use warnings;

use Devel::Peek qw( Dump );

use Inline C => <<'__EOI__';

AV* f() {
   return newAV();
}

__EOI__

Dump(f());

    [download]
    >perl -MInline=FORCE,NOISY,NOCLEAN a.pl
...
SV = IV(0x7bbf18) at 0x7bbf1c
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x7bc05c
  SV = PVAV(0x7bcec8) at 0x7bc05c
    REFCNT = 2         <--- XXX
    FLAGS = ()
    ARRAY = 0x0
    FILL = -1
    MAX = -1
    ARYLEN = 0x0
    FLAGS = (REAL)

    [download]

    Making it mortal doesn't help. So unless I'm missing something, this can only be used if you actually hold a reference to the array you return.

[reply]
[d/l]
[select]
      So unless I'm missing something, this can only be used if you actually hold a reference to the array you return

      No way to alter that particular reference count before returning the newly created AV ?

      Cheers,
      Rob
[reply]

        According to the example in the Inline C Cookbook, the correct way to return an AV* is:

        newRV_noinc( (SV*)array = newAV() )

        [download]

        Which kind of makes sense given the info ikegami posted above.

        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]

        I filed a ticket and was told that this is documented in perlxs.

        This is quite useful as it usually improves readability. While this works fine for an SV *, it's unfortunately not as easy to have AV * or HV * as a return value. You should be able to write: 

         AV *
 array()
     CODE:
         RETVAL = newAV();
         /* do something with RETVAL */
     OUTPUT:
         RETVAL

        [download]

        But due to an unfixable bug (fixing it would break lots of existing CPAN modules) in the typemap file, the reference count of the AV * is not properly decremented. Thus, the above XSUB would leak memory whenever it is being called. The same problem exists for HV *.

[reply]
[d/l]
[select]
        No. Decrementing its refcount before returning it would free it. One would normally make it a mortal, but I tried that and it didn't work.
[reply]

In Section Seekers of Perl Wisdom