两个.NET线程和硬件访问的问题

Question

我正在创建一个通过FT2232H USB/RS232转换器与设备通信的应用程序.对于通信我正在使用FTDI网站上的FTD2XX_NET.dll库.
我正在使用两个线程:

第一个线程连续从设备读取数据

第二个线程是Windows窗体应用程序的主线程

当我在接收器的线程运行时尝试将任何数据写入设备时,我遇到了问题.主线程只是挂起在ftdiDevice.Write函数上.

我尝试同步两个线程,以便只有一个线程可以同时使用读/写功能,但它没有帮助.

下面的代码负责沟通.请注意,以下函数是FtdiPort类的方法.

接收者的线程

        private void receiverLoop()
        {
            if (this.DataReceivedHandler == null)
            {
                throw new BackendException("dataReceived delegate is not set");
            }

            FTDI.FT_STATUS ftStatus = FTDI.FT_STATUS.FT_OK;
            byte[] readBytes = new byte[this.ReadBufferSize];

            while (true)
            {
                lock (FtdiPort.threadLocker)
                {
                    UInt32 numBytesRead = 0;

                    ftStatus = ftdiDevice.Read(readBytes, this.ReadBufferSize, ref numBytesRead);

                    if (ftStatus == FTDI.FT_STATUS.FT_OK)
                    {
                        this.DataReceivedHandler(readBytes, numBytesRead);
                    }
                    else
                    {
                        Trace.WriteLine(String.Format("Couldn't read data from ftdi: status {0}", ftStatus));
                        Thread.Sleep(10);
                    }                    
                }
                Thread.Sleep(this.RXThreadDelay);

            }
        }

从主线程调用的写函数

    public void Write(byte[] data, int length)
    {
        if (this.IsOpened)
        {
            uint i = 0;

            lock (FtdiPort.threadLocker)
            {
                this.ftdiDevice.Write(data, length, ref i);
            }

            Thread.Sleep(1);
            if (i != (int)length)
            {
                throw new BackendException("Couldnt send all data");
            }
        }
        else
        {
            throw new BackendException("Port is closed");
        }
    }






用于同步两个线程的对象


static Object threadLocker = new Object();


启动接收者线程的方法


        private void startReceiver()
        {
            if (this.DataReceivedHandler == null)
            {
                return;
            }
            if (this.IsOpened == false)
            {
                throw new BackendException("Trying to start listening for raw data while disconnected");
            }
            this.receiverThread = new Thread(this.receiverLoop);
            //this.receiverThread.Name = "protocolListener";
            this.receiverThread.IsBackground = true;
            this.receiverThread.Start();
        }

如果我评论以下行,ftdiDevice.Write函数不会挂起:


ftStatus = ftdiDevice.Read(readBytes, this.ReadBufferSize, ref numBytesRead);

Answer 1

另一种方法是使用FTDI的事件通知机制,这样您就不需要阻塞线程来读取数据:

public FTDISample()
{
    private AutoResetEvent receivedDataEvent;
    private BackgroundWorker dataReceivedHandler;
    private FTDI ftdi;

    public FTDISample(string serialNumber){
        ftdi = new FTDI();
        FTDI.FT_STATUS status = ftdi.OpenBySerialNumber(serialNumber);
        receivedDataEvent = new AutoResetEvent(false);
        status = mFTDI.SetEventNotification(FTDI.FT_EVENTS.FT_EVENT_RXCHAR, receivedDataEvent);
        dataReceivedHandler = new BackgroundWorker();
        dataReceivedHandler.DoWork += ReadData;
        if (!dataReceivedHandler.IsBusy)
        {
            dataReceivedHandler.RunWorkerAsync();
        }
    }

    private void ReadData(object pSender, DoWorkEventArgs pEventArgs)
    {
        UInt32 nrOfBytesAvailable = 0;
        while (true)
        {
            // wait until event is fired
            this.receivedDataEvent.WaitOne();

            // try to recieve data now
            FTDI.FT_STATUS status = ftdi.GetRxBytesAvailable(ref nrOfBytesAvailable);
            if (status != FTDI.FT_STATUS.FT_OK)
            {
                break;
            }
            if (nrOfBytesAvailable > 0)
            {
                byte[] readData = new byte[nrOfBytesAvailable];
                UInt32 numBytesRead = 0;
                status = mFTDI.Read(readData, nrOfBytesAvailable, ref numBytesRead);

                // invoke your own event handler for data received...
                //InvokeCharacterReceivedEvent(fParsedData);
            }
        }
    }

    public bool Write(string data)
    {
        UInt32 numBytesWritten = 0;
        ASCIIEncoding enconding = new ASCIIEncoding();
        byte[] bytes = enconding.GetBytes(data);
        FTDI.FT_STATUS status = ftdi.Write(bytes, bytes.Length, ref numBytesWritten);
        if (status != FTDI.FT_STATUS.FT_OK)
        {
            Debug.WriteLine("FTDI Write Status ERROR: " + status);
            return false;
        }
        if (numBytesWritten < data.Length)
        {
            Debug.WriteLine("FTDI Write Length ERROR: " + status + " length " + data.Length +
                            " written " + numBytesWritten);
            return false;
        }
        return true;
    }

Answer 2

一些东西：

1. 检查您的 Read 调用是否被阻塞。如果是这样，当 Read 阻塞等待响应时，您可能无法调用 Write。您的 API 文档可能对此有更多详细信息。

2. 某些 API 不能很好地支持多线程，即使在同步访问时也是如此。如果是这种情况，您可以使用将写入命令委托给通信线程的设计。当我过去使用这种模式时，我通常会将某种包含我希望写入的信息的 Command 类排队，并使用线程 Signal 类来允许我调用“命令”方法来阻止或提供某种类型的命令。异步通知。