# MCE task to run in parallel

sub work {
   my ($mce, $chunk_ref, $chunk_id) = @_;
   my $data = $chunk_ref->[0];
   my @ret = ();

   foreach my $chunk (@$data) {
      my %output = ();

      foreach my $key (keys %$chunk) {
         if ($key eq '.') {
            $output{$key} = $$chunk{$key};
            next;
         }
         my $val = $$chunk{$key};
         my $uc = uc($key);
         $val =~ s/$key/$uc/g;
         $output{$key} = $val;
      }

      push(@ret,\%output);
   }

   my $buf = '';

   foreach my $data (@ret) {
      foreach my $key (sort keys %$data) {
         $buf .= $$data{$key};
      }
      $buf .= "\n";
   }

   MCE->gather($chunk_id, $buf);
}

# make an output closure, returns an iterator

sub make_iter_output {
   my ($path) = @_;
   my %hold; my $order_id = 1;

   open my $fh, '>', $path or die "open error: $!";

   return sub {
      my $chunk_id = shift;

      # hold temporarily, until orderly
      $hold{$chunk_id} = $_[0];  # $buf

      while (1) {
         last unless exists($hold{$order_id});
         print {$fh} delete($hold{$order_id});

         $order_id++;
      }
   };
}