my $complex_data_structure = {'a'=>[1,2,3], 'b'=>{'c'=>[4,5,6],'d'=>LWP::UserAgent->new()}};
my $serialised_data = Sereal::Encoder::encode_sereal($complex_data_structure);
$pfm->finish(0, \$serialised_data); # <<< note that we pass a reference to our serialised-data.

##</code><code>##

my ($pid, $exit_code, $ident, $exit_signal, $core_dump, $data_structure_reference) = @_;
my $data = Sereal::Decoder::decode_sereal($$data_structure_reference); ## de-referencing the ref to the serialised data and then de-serialising.

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;

use Parallel::ForkManager;

use Data::Dump qw/dump/;

# bliako
use Sereal::Encoder qw(encode_sereal sereal_encode_with_object);
use Sereal::Decoder qw(decode_sereal sereal_decode_with_object);

my @names = ();
my %list = ();
my %thing = ();

my $threads = 20;

my $pfm = new Parallel::ForkManager( $threads );

my %results = ();
$pfm->run_on_finish( sub {
        my ($pid, $exit_code, $ident, $exit_signal, $core_dump, $data_structure_reference) = @_;
        my $data = Sereal::Decoder::decode_sereal($$data_structure_reference);
        # surely this is sequential code here so no need to lock %results, right?
        $results{$pid} = $data;
        # using pid as key is not a good idea because maybe a pid number will be eventually recycled.
});

my $things_hr = {
        'job1' => 'this is job 1 data',
        'job2' => 'this is job 2 data',
        'job3' => 'this is job 3 data',
        'job4' => 'this is job 4 data',
        'job5' => 'this is job 5 data',
};

THELOOP:
foreach my $thing(keys %{$things_hr}) {
        print "THING = $thing\n";
        $pfm->start and next THELOOP;
        my $pid = $$;
        my $returned_data = {
                'item1' => "item1 from pid $pid, for item $thing and value ".$things_hr->{$thing},
                'item2' => "item2 from pid $pid, for item $thing and value ".$things_hr->{$thing},
                "item3 are some array refs for pid: $pid", => [1,2,3,4],
        };
        my $serialised_data = Sereal::Encoder::encode_sereal($returned_data);
        print "pid=$pid, this is what I am sending:\n".dump($returned_data)."\n";
        $pfm->finish(0, \$serialised_data);
}
$pfm->wait_all_children;

print "Here are the results:\n".dump(%results)."\n";