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Paul Evans > Devel-Refcount-0.09 > Devel::Refcount



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Module Version: 0.09   Source   Latest Release: Devel-Refcount-0.10


Devel::Refcount - obtain the REFCNT value of a referent


 use Devel::Refcount qw( refcount );

 my $anon = [];

 print "Anon ARRAY $anon has " . refcount($anon) . " reference\n";

 my $otherref = $anon;

 print "Anon ARRAY $anon now has " . refcount($anon) . " references\n";


This module provides a single function which obtains the reference count of the object being pointed to by the passed reference value.


$count = refcount($ref)

Returns the reference count of the object being pointed to by $ref.


This function differs from Devel::Peek::SvREFCNT in that SvREFCNT() gives the reference count of the SV object itself that it is passed, whereas refcount() gives the count of the object being pointed to. This allows it to give the count of any referent (i.e. ARRAY, HASH, CODE, GLOB and Regexp types) as well.

Consider the following example program:

 use Devel::Peek qw( SvREFCNT );
 use Devel::Refcount qw( refcount );
 sub printcount
    my $name = shift;
    printf "%30s has SvREFCNT=%d, refcount=%d\n",
       $name, SvREFCNT($_[0]), refcount($_[0]);
 my $var = [];

 printcount 'Initially, $var', $var;
 my $othervar = $var;

 printcount 'Before CODE ref, $var', $var;
 printcount '$othervar', $othervar;
 my $code = sub { undef $var };
 printcount 'After CODE ref, $var', $var;
 printcount '$othervar', $othervar;

This produces the output

                Initially, $var has SvREFCNT=1, refcount=1
          Before CODE ref, $var has SvREFCNT=1, refcount=2
                      $othervar has SvREFCNT=1, refcount=2
           After CODE ref, $var has SvREFCNT=2, refcount=2
                      $othervar has SvREFCNT=1, refcount=2

Here, we see that SvREFCNT() counts the number of references to the SV object passed in as the scalar value - the $var or $othervar respectively, whereas refcount() counts the number of reference values that point to the referent object - the anonymous ARRAY in this case.

Before the CODE reference is constructed, both $var and $othervar have SvREFCNT() of 1, as they exist only in the current lexical pad. The anonymous ARRAY has a refcount() of 2, because both $var and $othervar store a reference to it.

After the CODE reference is constructed, the $var variable now has an SvREFCNT() of 2, because it also appears in the lexical pad for the new anonymous CODE block.


An XS implementation of this function is provided, and is used by default. If the XS library cannot be loaded, a fallback implementation in pure perl using the B module is used instead. This will behave identically, but is much slower.

        Rate   pp   xs
 pp 225985/s   -- -66%
 xs 669570/s 196%   --



Paul Evans <>

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