Threads in C#

[alexdevmaster]

Im trying to write a program that talks to a usb device. Opening the usb port and sending and receiving data is not the problem, the problem is sharing the connection to the usb across threads. I have button that willl send data entered in a text box to the device. What I want to be able to is to have a thread constantly checking usb connection for data incoming from the device and I want it to run and write its findings to a listbox while still allowing me the ability to send data when I want to.

I created a thread that executes a function that just sits in a loop listening for incoming data. The problem with this is that I start the thread after opening the usb connection and writing some data to the device. The usb connection is global so I am assuming that my poll function should be able to see it. Unfortunately although I know I assigned the global variable to a connection, the thread is reporting it as null and I cant open a new connection in the thread because only one connection can be opened to the device at a time.

The only solution I can think of using something like a mutex, where I would acquire rights to use the usb port when I want to write and when Im finished I would let go of it and allow the thread to acquire its own connection. That sounds like too much trouble than its worth. Please see code below.

private Thread workerThread = null;
UsbOtiNet usb = null;

public Form1()
{
	...
}

.
.

private void btnRun_Click(object sender, System.EventArgs e)
{
	Display ("--- Demo Starts ---");

	// Create Object
	UsbOtiNet usb = new UsbOtiNet();

	// Connect to Reader
	bool bOK;
	bOK = usb.Open();
	if (!bOK)
	{
		Display ("*** Failed connecting to Reader: " + usb.LastErrorString);
		// Close Connection
		usb.Close();
		return;
	}
	Display ("Connect - OK");

	// start listening for incoming usb traffic.
	workerThread = new Thread(new ThreadStart(this.Poll));
	workerThread.Start();	

	// Send ASCII Data 
	//byte[] baMODE0 = {0x4D,0x4F,0x44,0x45,0x30}; // binary representation of "MODE0"
	string hexString = textBox1.Text;
	int discarded;
	byte[] baMODE0 = HexEncoding.GetBytes(hexString, out discarded);
		

	// byte[] baMODE0 = {0x02,0x0A,0x00,0x3E,0xDF, 0x7E, 0x01, 0x01, 0x97, 0x03};
	bOK = usb.Write(baMODE0);
	if (!bOK)
	{
		Display ("*** Failed sending data to the Reader: " + usb.LastErrorString);

	}
	else
	{
		Display ("Write (" + hexString + ") - OK");
	}


}

void Poll()
{
	while(true)
	{
		if(usb != null)
		{
			usb.Timeout = 400;

			// Read Data
			int BytesRead = usb.Read(20);
			if (BytesRead != 0)
				Display ("Read() received: " + HexEncoding.ToString( usb.InputStream ));
		}
		else
			Display("usb is {null}");
	}
}

void Display (string msg)
{
	int RowNumber = lstMsg.Items.Add (msg);
	lstMsg.SelectedIndex = RowNumber;
}

private void Form1_Load(object sender, System.EventArgs e)
{
			
}

private void btnStop_Click(object sender, System.EventArgs e)
{
	if(workerThread != null)
	{
		// stop the thread
		workerThread.Abort();
	}

	// Close Connection
	if(usb != null)
		 usb.Close();

	Display ("--- Demo Ends ---");
	Display ("");
}

}

[leoandru]

Here is your problem

UsbOtiNet usb = new UsbOtiNet();

Should be:

usb = new UsbOtiNet();

[alexdevmaster]

hmm.. how did i not see that! happens to the best of us, thanks!

[leoandru]

yup we make mistakes like that all the time.. wasted hours on recoding and what not because of that. Thats when I learned to use the degugger its helps a lot in situations like these; you would find the error within couple minutes of debuging.