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=head1 NAME
Sys::Statistics::Linux::PgSwStats - Collect linux paging and swapping statistics.
=head1 SYNOPSIS
    use Sys::Statistics::Linux::PgSwStats;
    my $lxs = Sys::Statistics::Linux::PgSwStats->new;
    $lxs->init;
    sleep 1;
    my $stat = $lxs->get;
=head1 DESCRIPTION
Sys::Statistics::Linux::PgSwStats gathers paging and swapping statistics from the virtual F</proc> filesystem (procfs).
For more informations read the documentation of the front-end module L<Sys::Statistics::Linux>.
=head1 PAGING AND SWAPPING STATISTICS
Generated by F</proc/stat> or F</proc/vmstat>.
    pgpgin      -  Number of kilobytes the system has paged in from disk per second.
    pgpgout     -  Number of kilobytes the system has paged out to disk per second.
    pswpin      -  Number of kilobytes the system has swapped in from disk per second.
    pswpout     -  Number of kilobytes the system has swapped out to disk per second.
    The following statistics are only available by kernels from 2.6.
    pgfault     -  Number of page faults the system has made per second (minor + major).
    pgmajfault  -  Number of major faults per second the system required loading a memory page from disk.
=head1 METHODS
=head2 new()
Call C<new()> to create a new object.
    my $lxs = Sys::Statistics::Linux::PgSwStats->new;
=head2 init()
Call C<init()> to initialize the statistics.
    $lxs->init;
=head2 get()
Call C<get()> to get the statistics. C<get()> returns the statistics as a hash reference.
    my $stat = $lxs->get;
=head1 EXPORTS
No exports.
=head1 SEE ALSO
B<proc(5)>
=head1 REPORTING BUGS
Please report all bugs to <jschulz.cpan(at)bloonix.de>.
=head1 AUTHOR
Jonny Schulz <jschulz.cpan(at)bloonix.de>.
=head1 COPYRIGHT
Copyright (c) 2006, 2007 by Jonny Schulz. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
=cut
package Sys::Statistics::Linux::PgSwStats;
our $VERSION = '0.13';
use strict;
use warnings;
use Carp qw(croak);
use Time::HiRes;
sub new {
    my $class = shift;
    my %self = (
        files => {
            stat   => '/proc/stat',
            vmstat => '/proc/vmstat',
        }
    );
    return bless \%self, $class;
}
sub init {
    my $self = shift;
    $self->{time} = Time::HiRes::gettimeofday();
    $self->{init} = $self->_load;
}
sub get {
    my $self  = shift;
    my $class = ref $self;
    if (!exists $self->{init}) {
        croak "$class: there are no initial statistics defined";
    }
    $self->{stats} = $self->_load;
    $self->_deltas;
    return $self->{stats};
}
#
# private stuff
#
sub _load {
    my $self  = shift;
    my $class = ref $self;
    my $file  = $self->{files};
    my %stats = ();
    open my $fh, '<', $file->{stat} or croak "$class: unable to open $file->{stat} ($!)";
    while (my $line = <$fh>) {
        if ($line =~ /^page\s+(\d+)\s+(\d+)$/) {
            @stats{qw(pgpgin pgpgout)} = ($1, $2);
        } elsif ($line =~ /^swap\s+(\d+)\s+(\d+)$/) {
            @stats{qw(pswpin pswpout)} = ($1, $2);
        }
    }
    close($fh);
    # if paging and swapping are not found in /proc/stat
    # then let's try a look into /proc/vmstat (since 2.6)
    if (!defined $stats{pswpout}) {
        open my $fh, '<', $file->{vmstat} or croak "$class: unable to open $file->{vmstat} ($!)";
        while (my $line = <$fh>) {
            next unless $line =~ /^(pgpgin|pgpgout|pswpin|pswpout|pgfault|pgmajfault)\s+(\d+)/;
            $stats{$1} = $2;
        }
        close($fh);
    }
    return \%stats;
}
sub _deltas {
    my $self  = shift;
    my $class = ref $self;
    my $istat = $self->{init};
    my $lstat = $self->{stats};
    my $time  = Time::HiRes::gettimeofday();
    my $delta = sprintf('%.2f', $time - $self->{time});
    $self->{time} = $time;
    while (my ($k, $v) = each %{$lstat}) {
        if (!defined $istat->{$k} || !defined $lstat->{$k}) {
            croak "$class: not defined key found '$k'";
        }
        if ($v !~ /^\d+\z/ || $istat->{$k} !~ /^\d+\z/) {
            croak "$class: invalid value for key '$k'";
        }
        $lstat->{$k} =
            $lstat->{$k} == $istat->{$k}
                ? sprintf('%.2f', 0)
                : $delta > 0
                    ? sprintf('%.2f', ($lstat->{$k} - $istat->{$k}) / $delta)
                    : sprintf('%.2f', $lstat->{$k} - $istat->{$k});
        $istat->{$k}  = $v;
    }
}
1;