从串口线程安全解析数据

Question

我从串口读取数据并在一个单独的类中解析它。然而，数据被错误地解析，一些样本被重复，而另一些则丢失了。

这是一个解析数据包的例子。它从 packetIndex 开始（应该从 1 开始并递增）。您可以看到 packetIdx 如何重复，以及其他一些值如何重复。我认为这是由于多线程造成的，但我不确定如何解决。

    2 -124558.985180734 -67934.4168823262 -164223.049786454 -163322.386243628
    2 -124619.580759952 -67962.535376851 -164191.757344217 -163305.68949052
    3 -124685.719571795 -67995.8394760894 -164191.042088394 -163303.119039907 
    5 -124801.747477263 -68045.7062179692 -164195.288919841 -163299.140429394 
    6 -124801.747477263 -68045.7062179692 -164221.105184687 -163297.46404856 
    6 -124832.8387538 -68041.9287731563 -164214.936103217 -163294.983004926 

这是我应该收到的：

1 -124558.985180734 -67934.4168823262 -164223.049786454 -163322.386243628
2 -124619.580759952 -67962.535376851 -164191.757344217 -163305.68949052
3 -124685.719571795 -67995.8394760894 -164191.042088394 -163303.119039907 
4 -124801.747477263 -68045.7062179692 -164195.288919841 -163299.140429394 
 ...

这是 SerialPort_DataReceived

 public void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
    {
        lock (_lock)
        {
            byte[] buffer = new byte[_serialPort1.BytesToRead];
            _serialPort1.Read(buffer, 0, buffer.Length);

            for (int i = 0; i < buffer.Length; i++)
            {
                //Parse data
                double[] samplesAtTimeT = DataParserObj.interpretBinaryStream(buffer[i]);
                //Add data to BlockingCollection when parsed 
                if (samplesAtTimeT != null)
                    _bqBufferTimerSeriesData.Add(samplesAtTimeT);
            }
        }
    }

以及解析数据的类：

public class DataParser
{
    private int packetSampleCounter = 0;
    private int localByteCounter = 0;
    private int packetState = 0;
    private byte[] tmpBuffer = new byte[3];
    private double[] ParsedData = new double[5]; //[0] packetIdx (0-255), [1-4] signal


    public double[] interpretBinaryStream(byte actbyte)
    {
        bool returnDataFlag = false;

        switch (packetState)
        {
            case 0: // end packet indicator
                if (actbyte == 0xC0)
                    packetState++;
                break;
            case 1: // start packet indicator
                if (actbyte == 0xA0)
                    packetState++;
                else
                    packetState = 0;
                break;
            case 2: // packet Index 
                packetSampleCounter = 0;
                ParsedData[packetSampleCounter] = actbyte;
                packetSampleCounter++;
                localByteCounter = 0;
                packetState++;
                break;
            case 3: //channel data (4 channels x 3byte/channel)
                // 3 bytes
                tmpBuffer[localByteCounter] = actbyte;
                localByteCounter++;
                if (localByteCounter == 3)
                {
                    ParsedData[packetSampleCounter] = Bit24ToInt32(tmpBuffer);
                    if (packetSampleCounter == 5)
                        packetState++; //move to next state, end of packet
                    else
                        localByteCounter = 0;
                }
                break;
            case 4: // end packet
                if (actbyte == 0xC0)
                {
                    returnDataFlag = true;
                    packetState = 1;
                }
                else
                    packetState = 0;
                break;
            default:
                packetState = 0;
                break;
        }
        if (returnDataFlag)
            return ParsedData;
        else
            return null;
    }
}

Answer 1

摆脱DataReceived 事件，改为使用await serialPort.BaseStream.ReadAsync(....) 来在数据进入时获得通知。async/await 更简洁，不会强迫您进行多线程数据处理。对于高速网络，并行处理非常棒。但是串口很慢，所以额外的线程没有任何好处。

另外，BytesToRead 有问题（它会返回排队的字节数，但会破坏其他状态），你永远不应该调用它。

最后，不要忽略来自Read（或BaseStream.ReadAsync）的返回值。您需要知道字节实际上是如何放入缓冲区的，因为不能保证与您要求的数字相同。

private async void ReadTheSerialData()
{
     var buffer = new byte[200];
     while (serialPort.IsOpen) {
         var valid = await serialPort.BaseStream.ReadAsync(buffer, 0, buffer.Length);
         for (int i = 0; i < valid; ++i)
         {
             //Parse data
            double[] samplesAtTimeT = DataParserObj.interpretBinaryStream(buffer[i]);
            //Add data to BlockingCollection when parsed 
            if (samplesAtTimeT != null)
                _bqBufferTimerSeriesData.Add(samplesAtTimeT);
         }
     }
}

在打开端口并设置好流控、超时等后调用该函数，你可能会发现不再需要阻塞队列，直接处理samplesAtTimeT的内容即可。