#!/usr/bin/perl
use 5.16.0;
use threads;

sub open_for_read($) {
  open(my $handle, "<$_[0]") or die "opening $_[0]: $!";
  $handle }

sub ticks_all {
  my $f = open_for_read("/proc/stat");
  return (split ' ', <$f>)[1,3] }

sub ticks_process() {
  my $f = open_for_read("/proc/self/stat");
  return (split ' ', <$f>)[13,14] }

sub dowork () {
  use Digest::MD5;
  my $d = Digest::MD5->new;
  $d->add('nobody inspects');
  $d->add(' the spammish repetition') for (0 .. 10_000_000)} 

my ($before_all_user, $before_all_sys) = ticks_all();
my ($before_process_user, $before_process_sys) = ticks_process();

my @threads; 
for my $i (0 .. 8) {
  my $t = threads->create(\&dowork);
  push @threads,$t }
$_->join() foreach @threads;

my ($after_all_user, $after_all_sys) = ticks_all();
my ($after_process_user, $after_process_sys) = ticks_process();

#(note: changing perl defaults for print)
$, = " ";   #put spaces between output fields
$\ = "\n";  #add LF to end of lines by default

print 'delta process: user:', $after_process_user - $before_process_user, 
      ' sys:', $after_process_sys - $before_process_sys;
print 'delta all: user:', $after_all_user - $before_all_user, 
      ' sys: ', $after_all_sys - $before_all_sys;