Perl using Win32::PerfLib - perl

Question

I'm trying to understand Win32::PerfLib better, and I mustn't use Win32::PerfMon.
Two example I have questions about:
First example, is the classic from CPAN:
use Win32::PerfLib;
my $server = "";`enter code here`
Win32::PerfLib::GetCounterNames($server, \%counter);
%r_counter = map { $counter{$_} => $_ } keys %counter;
# retrieve the id for process object
$process_obj = $r_counter{Process};
# retrieve the id for the process ID counter
$process_id = $r_counter{'ID Process'};
# create connection to $server
$perflib = new Win32::PerfLib($server);
$proc_ref = {};
# get the performance data for the process object
$perflib->GetObjectList($process_obj, $proc_ref);
$perflib->Close();
$instance_ref = $proc_ref->{Objects}->{$process_obj}->{Instances};
foreach $p (sort keys %{$instance_ref})
{
$counter_ref = $instance_ref->{$p}->{Counters};
foreach $i (keys %{$counter_ref})
{
if($counter_ref->{$i}->{CounterNameTitleIndex} == $process_id)
{
printf( "% 6d %s\n", $counter_ref->{$i}->{Counter},
$instance_ref->{$p}->{Name}
);
}
}
}
Could someone explain in depth the 4th line?
I didn't understand why we use $_ for and
what it represents, although I read about it
but in this case I don't know. In addition
what's the $counter{$_} => $_ meaning?
Second question is from this code, which gets the cpu %
from perfmon:
use Win32::PerfLib;
($server) = #ARGV;
# only needed for PrintHash subroutine
#Win32::PerfLib::GetCounterNames($server, \%counter);
$processor = 238;
$proctime = 6;
$perflib = new Win32::PerfLib($server);
$proc_ref0 = {};
$proc_ref1 = {};
$perflib->GetObjectList($processor, $proc_ref0);
sleep 5;
$perflib->GetObjectList($processor, $proc_ref1);
$perflib->Close();
$instance_ref0 = $proc_ref0->{Objects}->{$processor}->{Instances};
$instance_ref1 = $proc_ref1->{Objects}->{$processor}->{Instances};
foreach $p (keys %{$instance_ref0})
{
$counter_ref0 = $instance_ref0->{$p}->{Counters};
$counter_ref1 = $instance_ref1->{$p}->{Counters};
foreach $i (keys %{$counter_ref0})
{
next if $instance_ref0->{$p}->{Name} eq "_Total";
if($counter_ref0->{$i}->{CounterNameTitleIndex} == $proctime)
{
$Numerator0 = $counter_ref0->{$i}->{Counter};
$Denominator0 = $proc_ref0->{PerfTime100nSec};
$Numerator1 = $counter_ref1->{$i}->{Counter};
$Denominator1 = $proc_ref1->{PerfTime100nSec};
$proc_time{$p} = (1- (($Numerator1 - $Numerator0) /
($Denominator1 - $Denominator0 ))) * 100;
printf "Instance $p: %.2f\%\n", $proc_time{$p};
}
}
}
Why does the programmer had to use the method "GetObjectList"
Two times and put the sleep method between them?
And why we can't just take the cpu percent like perfmon shows
and we have to make all those calculations?
Thanks in advance,
Fam Pam.

Answer 1

In this code:
Win32::PerfLib::GetCounterNames($server, \%counter);
%r_counter = map { $counter{$_} => $_ } keys %counter;
You are stroing the perfdata in %counter hash. The map in this case creates a reverse hash where the earlier values becomes keys.
Example:
from apple => 'fruit' to fruit => 'apple