I got this working, but only for a single data set.I forgot there was another foreach loop going on in one of the "dostuff" sections which is creating a multi dimensional array.

The problem becomes, how do I return a multidimensional array in its entirety back to the parent?

#pseudo code

use Parallel::ForkManager;

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

$threads = 20

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


$pfm->run_on_finish( sub {
    my ($pid, $exit_code, $ident, $exit_signal, $core_dump, $data_stru
+cture_reference) = @_;

        my $name = $data_structure_reference->{name};
    %list = $data_structure_reference->{data1};
        $thing{$name}{a} = $data_structure_reference->{thing1};
    $thing{$name}{b} = $data_structure_reference->{thing2};
    
    push @names, $data_structure_reference->{name};
    
  
});
});
FOREACH: foreach my $thing(keys %{$things_hr}) {

    my $pid = $pfm->start and next;

#do stuff

        push @names, $name;
#do stuff

    $thing1{$name}{a} = $value1;
    $thing{$name}{b} = $value2;

#do stuff
    Foreach $id:{

    $list{$id}{$name}{b} = $b;
    $list{$id}{$name}{e} = $b1;
    $list{$id}{$name}{a} = 0;
    $list{$id}{$name}{c} = $ar->[$id][3];
    $list{$id}{$name}{i} = $ar->[$id][1];
    $list{$id}{$name}{j} = $ar->[$id][2];
    $list{$id}{$name}{k} = sprintf("%.4f",$ar->[$id][9]);
}

$pfm->finish( 0, { data1 => %id, 
           name => $sample_name,
                  thing1 => $value1, 
           thing2 => $value2,});
   

  

$pfm->wait_all_children;
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