#! perl -slw
use strict;
use threads;
use Thread::Queue;

my $directories = Thread::Queue->new();
my $files = Thread::Queue->new();

use vars '$NUM_CPUS';
$NUM_CPUS ||= 4;

sub _walk {
    while( defined my $dir = $directories->dequeue) {;
        my @entries = ...;
        for my $e (@entries) {
            if( -d $e ) {
                # depth-first search
                $directories->insert(0, $e);
            } else {
                # It would be much faster to enqueue all files in bulk instead
                # of enqueueing them one by one, but first get it working before
                # you make it fast
                $files->enqueue( $e );
            };
        };
    };
}

$directories->enqueue( @ARGV );

for ( 1..$NUM_CPUS ) {
    threads->new( \&_walk )->detach;
};

print while defined( $_ = $files->dequeue );

print 'Done';