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.\" ========================================================================
.\"
.IX Title "B::COW 3pm"
.TH B::COW 3pm "2020-11-08" "perl v5.32.0" "User Contributed Perl Documentation"
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.SH "NAME"
B::COW \- B::COW additional B helpers to check COW status
.SH "VERSION"
.IX Header "VERSION"
version 0.004
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #!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 = ( \*(Aqa\*(Aq .. \*(Aqd\*(Aq );
\&         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;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
B::COW provides some naive additional B helpers to check the \s-1COW\s0 status of one SvPV.
.SS "\s-1COW\s0 or Copy On Write introduction"
.IX Subsection "COW or Copy On Write introduction"
A COWed SvPV is sharing its string (the \s-1PV\s0) with other SvPVs.
It's a (kind of) Read Only C string, that would be Copied On Write (\s-1COW\s0).
.PP
More than one \s-1SV\s0 can share the same \s-1PV,\s0 but when one \s-1PV\s0 need to alter it,
it would perform a copy of it, decrease the \s-1COWREFCNT\s0 counter.
.PP
One \s-1SV\s0 can then drop the \s-1COW\s0 flag when it's the only one holding a pointer
to the \s-1PV.\s0
.PP
The \s-1COWREFCNT\s0 is stored at the end of the \s-1PV,\s0 after the the \*(L"\e0\*(R".
.PP
That value is limited to 255, when we reach 255, a new \s-1PV\s0 would be created,
.SH "FUNCTIONS"
.IX Header "FUNCTIONS"
.SS "\fBcan_cow()\fP"
.IX Subsection "can_cow()"
Return a boolean value. True if your Perl version support Copy On Write for SvPVs
.SS "is_cow( \s-1PV\s0 )"
.IX Subsection "is_cow( PV )"
Return a boolean value. True if the \s-1SV\s0 is cowed SvPV. (check the \s-1SV FLAGS\s0)
.SS "cowrefcnt( \s-1PV\s0 )"
.IX Subsection "cowrefcnt( PV )"
Return one integer representing the \s-1COW\s0 RefCount value.
If the string is not \s-1COW,\s0 then it will return undef.
.SS "\fBcowrefcnt_max()\fP"
.IX Subsection "cowrefcnt_max()"
Will return the \s-1SV_COW_REFCNT_MAX\s0 of your Perl. (if \s-1COW\s0 is supported, this should
be 255 unless customized).
.SH "AUTHOR"
.IX Header "AUTHOR"
Nicolas R. <atoomic@cpan.org>
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
This software is copyright (c) 2018 by Nicolas R.
.PP
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.