@Override
    public List<Runnable> shutdownNow() {
        List<Runnable> rs = new ArrayList<Runnable>();
        _queue.drainTo(rs);
        for (Worker w : _workers) {
            Runnable r = w._runnable;
            w.shutdown();
            w._thread.interrupt();

            if (r != null) {
                rs.add(r);
            }
        }
        return rs;
    }