B::COW(3) User Contributed Perl Documentation B::COW(3)
NAME
B::COW - B::COW additional B helpers to check COW status
VERSION
version 0.007
SYNOPSIS
#!perl
use strict;
use warnings;
use Test::More; # just used for illustration purpose
use B::COW qw{:all};
if ( can_cow() ) { # $] >= 5.020
ok !is_cow(undef);
my $str = "abcdef";
ok is_cow($str);
is cowrefcnt($str), 1;
my @a;
push @a, $str for 1 .. 100;
ok is_cow($str);
ok is_cow( $a[0] );
ok is_cow( $a[99] );
is cowrefcnt($str), 101;
is cowrefcnt( $a[-1] ), 101;
delete $a[99];
is cowrefcnt($str), 100;
is cowrefcnt( $a[-1] ), 100;
{
my %h = ( 'a' .. 'd' );
foreach my $k ( sort keys %h ) {
ok is_cow($k);
is cowrefcnt($k), 0;
}
}
}
else {
my $str = "abcdef";
is is_cow($str), undef;
is cowrefcnt($str), undef;
is cowrefcnt_max(), undef;
}
done_testing;
DESCRIPTION
B::COW provides some naive additional B helpers to check the COW status
of one SvPV.
COW or Copy On Write introduction
A COWed SvPV is sharing its string (the PV) with other SvPVs. It's a
(kind of) Read Only C string, that would be Copied On Write (COW).
More than one SV can share the same PV, but when one PV need to alter
it, it would perform a copy of it, decrease the COWREFCNT counter.
One SV can then drop the COW flag when it's the only one holding a
pointer to the PV.
The COWREFCNT is stored at the end of the PV, after the the "\0".
That value is limited to 255, when we reach 255, a new PV would be
created,
FUNCTIONS
can_cow()
Return a boolean value. True if your Perl version support Copy On Write
for SvPVs
is_cow( PV )
Return a boolean value. True if the SV is cowed SvPV. (check the SV
FLAGS)
cowrefcnt( PV )
Return one integer representing the COW RefCount value. If the string
is not COW, then it will return undef.
cowrefcnt_max()
Will return the SV_COW_REFCNT_MAX of your Perl. (if COW is supported,
this should be 255 unless customized).
AUTHOR
Nicolas R. <atoomic@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2018 by Nicolas R.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
perl v5.34.3 2024-03-12 B::COW(3)
b-cow 0.7.0 - Generated Fri Apr 3 07:47:58 CDT 2026