use strict;
use warnings;
use feature 'say';

use threads;
use MCE::Shared;

my $var = MCE::Shared->scalar(0);

sub task {
    for ( 1 .. 2000 ) {
        $var->incr;
        $var->incrby(4);
    }
}

threads->create(\&task) for 1 .. 4;
$_->join for threads->list;

say $var->get;  # 40000