public void set (int option_, int optval_)
    {
        if (option_ == ZMQ.ZMQ_MAX_SOCKETS && optval_ >= 1) {
            opt_sync.lock ();
            max_sockets = optval_;
            opt_sync.unlock ();
        }
        else
        if (option_ == ZMQ.ZMQ_IO_THREADS && optval_ >= 0) {
            opt_sync.lock ();
            io_thread_count = optval_;
            opt_sync.unlock ();
        }
        else {
            throw new IllegalArgumentException("option = " + option_);
        }
    }