gistfile1.pl

#!/usr/bin/env perl

use FindBin;
# PERL5LIB
use lib "$FindBin::Bin/../lib";
use lib "$FindBin::Bin/../thirdparty/lib/perl5";

use Mojo::IOLoop::ForkCall;
use Data::Dumper;

my @fc;
for my $id (1..2) {
    my $fc = Mojo::IOLoop::ForkCall->new;
    push @fc, $fc; #keep fc in scope
    my $pid = $fc->run(
        sub {
            my $arg = shift;
            warn "$id ($$): start sleep\n";
            sleep 2;
            warn "$id ($$): end sleep\n";
            return ({complex=>'data',id=>$id},$arg);
        },
        ["Scalar $id"],
        sub {
            my ($fc, $err, @return) = @_;
            warn "$id ($$): return: ".Dumper \@return;
            warn "$id ($$): error: $err\n" if $err;
        }
    );
};

Mojo::IOLoop->start;

gistfile2.txt

1 (8444): start sleep
1 (8445): return: $VAR1 = [];
1 (8445): error: Magic number checking on storable string failed at /usr/lib/perl/5.14/Storable.pm line 416, at /home/oetiker/checkouts/znapzend/bin/../thirdparty/lib/perl5/Mojo/IOLoop/ForkCall.pm line 80

2 (8445): start sleep
1 (8444): end sleep
1 (8443): return: $VAR1 = [
          {
            'complex' => 'data',
            'id' => '1'
          },
          'Scalar 1'
        ];
2 (8445): end sleep
2 (8443): return: $VAR1 = [
          {
            'complex' => 'data',
            'id' => '2'
          },
          'Scalar 2'
        ];