use strict;
use warnings;
use Parallel::ForkManager;
use Test::More qw( no_plan );
use Data::Dumper;


my $letters = [ qw(a b c) ];

# the order of the concatenated letters doesn't matter, as long as we get all three letters
my $content;

ok( index( $content = concatenate_parallel($letters), 'b' ) > 0, "it contains b, total content: $content"  ); # fast, but doesn't work
ok( index( $content = concatenate_serial($letters), 'b' ) > 0, "it contains b, total content: $content"  ); # works, but slow



#works, but slow
sub concatenate_serial {
  my $letters = shift;
  my $content='';

  foreach my $letter ( @$letters ) {
    sleep 3; #something happens that takes noticeable time, like fetch a url
    $content .= $letter;
  }
  print "serial content: $content\n";
  return $content
}

# fast, but doesn't work
sub concatenate_parallel {
  my $letters = shift;
  my $pm=new Parallel::ForkManager(10);

  my $content='';
  foreach my $letter ( @$letters ) {
    $pm->start and next;

    sleep 3; #something happens that takes time, like fetch a url
    $content .= $letter;

    $pm->finish;
  }
  $pm->wait_all_children;
  return $content
}