#!/usr/bin/env perl

use strict;
use warnings;
use threads;
use threads::shared;
use Thread::Semaphore;
use Math::BigInt;
use Data::Dump;
use feature qw(say);

my @numbers = ( 1 .. 10 );
my %result : shared;
my $semaphore = Thread::Semaphore->new(4);

my @threads = map {
    $semaphore->down;
    threads->create( \&process, $_ );
} @numbers;

$_->join for @threads;

dd \%result;

sub process {
    my $number    = shift;
    my $factorial = factorial($number);
    say qq($number $factorial);
    eval { $result{$number} = $factorial; };
    say $@ if $@;
    $semaphore->up;
}

sub factorial {
    my $number = shift;
    Math::BigInt->bfac($number);
}

__END__

karls-mac-mini:monks karl $ ./semaphore.pl 
...
10 3628800
Invalid value for shared scalar at ./semaphore.pl line 29.
...