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

my @threads =
   map {
      async { # Just nicer
         # You don't want dequeue_nb here!!!
         while ( defined( my $item = $q->dequeue() ) ) {
            # Don't kill the entire thread
            # if there's a problem with one job.
            eval { worker( $item ); 1 } or warn( $@ );
         }
      };
   }
      1 .. $thread_limit;

# Do this *after* the threads are created.
# Otherwise, you could have a deadlock.
# (Ok, not really since we don't place a size
# limit on the queue so the queue can grow
# to any size, but it's still nicer and
# allows us to limit the size of the queue.)
$q->enqueue( substr $_, 0, 6 ) for @file;

# Make it so the threads exit when the queue becomes empty.
$q->end;

$_->join() for @threads;