use 5.010;
use Time::HiRes qw(time);

my $data = 'x' x 500 * 1024**2;

my $t    = time;
for my $n ( 1 .. 100 ) {
    unless (fork) {
        substr( $data, 4096 * $_ + $n, 1 ) |= 1 for 0 .. 124;
        exit;
    }
}
waitall;

say time - $t;

##</code><code>##

<code>
use strict;
use warnings;
use 5.010;
use Time::HiRes qw(time);

my $data = 'x' x 500 * 1024**2;

my $t    = time;
for my $n ( 1 .. 100 ) {
    unless (fork) {
        substr( $data, 4096 * $_ + $n, 1 ) |= chr(1) for 0 .. 124;
        exit;
    }
}
waitall;

say time - $t;

##</code><code>##

#! perl -slw
use strict;
use 5.010;
use threads ( stack_size => 4096 );
use Thread::Queue;
use Time::HiRes qw(time);

use constant DATA_SIZE => (500 * 1024**2);

sub thread {
    my( $Q, $n ) = @_;
    $Q->enqueue( 4096 * $_ + $n ) for 0 .. 124;
    $Q->enqueue( undef );
}

my $t    = time;
my $Q = new Thread::Queue;
my @t = map threads->create( \&thread, $Q, $_ ), 1 .. 100;

my $data = 'x' x DATA_SIZE ;

for(1..100) {
    substr( $data, $_, 1 ) |= chr(1) while $_ = $Q->dequeue;
}

$_->join for @t;

say time - $t;

printf "%d bits changed\n", DATA_SIZE  - ( $data =~ tr[x][] );
__END__
c:\test>junk44
2.03600001335144
12500 bits changed