C# problem with two threads and hardware access

Posted by mack369 on Stack Overflow See other posts from Stack Overflow or by mack369
Published on 2010-03-13T16:47:36Z Indexed on 2010/03/13 16:55 UTC
Read the original article Hit count: 376

Filed under:

hardware-interface

I'm creating an application which communicates with the device via FT2232H USB/RS232 converter. For communication I'm using FTD2XX_NET.dll library from FTDI website.
I'm using two threads:

first thread continuously reads data from the device

the second thread is the main thread of the Windows Form Application

I've got a problem when I'm trying to write any data to the device while the receiver's thread is running. The main thread simply hangs up on ftdiDevice.Write function.

I tried to synchronize both threads so that only one thread can use Read/Write function at the same time, but it didn't help.

Below code responsible for the communication. Note that following functions are methods of FtdiPort class.

Receiver's thread


        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);

            }
        }

Write function called from main thread



    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");
        }
    }

Object used to synchronize two threads


static Object threadLocker = new Object();

Method that starts the receiver's thread


        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();
        }

The ftdiDevice.Write function doesn't hang up if I comment following line:

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

Developer IT