queue lock

// main
{
    ..
    motor1.ORDER_move()
    ..
}

class Motor()
{
..
    public void ORDER_move()
    {
            byte[] cmd = ...;
            BackgroundWorker worker = new BackgroundWorker();
            worker.DoWork += worker_DoWork;
            worker.RunWorkerAsync((object)cmd);
    }

        private void worker_DoWork(object sender, DoWorkEventArgs e)
        {
            lock(queue_lock)
            {
                C_SPI.AppendDataToQueue(e.Argument as byte[]);
            }
            lock(spi_lock)
            {
                C_SPI.WriteDataFromQueue();
            }
        }
}

class C_SPI()
{
    // schematicky definice
    private queue cmd_que;  // fifo fronta
    private serialport spi;
    object queue_lock;
    object spi_lock;


    public void AppendDataToQueue(byte[] cmd)
    {
                lock (queue_lock)
                {
            queue.append(cmd);
        }
    }
    public void WriteDataFromQueue()
    {
                lock (spi_locker)
                {
            spi.write(queue.getLast);
        }
    }
}