#! perl -slw
use strict;
use Time::HiRes qw[ time ];
use threads;

<>;
my $start = time;

async {
    my $s = chr(0) x 1000;
    for( 1 .. 5e5 ) {
        $s .= chr( 0 ) x 1000;
    }
}->detach;

my $s = chr(0) x 1000;
for( 1 .. 5e5 ) {
    $s .= chr( 0 ) x 1000;
}

printf "Re-allocated 2 x 500MB (in 1000 byte incements) on two threads in %.3f\n",
    time() - $start;

<>;

__END__
C:\perl\5.10.1\bin>.\perl.exe \test\mem.pl

Re-allocated 2 x 500MB (in 1000 byte incements) on two threads in 2.416