Develop Reference

How to recreate a possible deadlock that happens on winforms c# app

So I've recently come across a what I think is a deadlock that only happens sometimes. After I close my form the app just hangs. I'm using SerialPorts for communication. I've read this answer and this answer which both suggest I use BeginInvoke() instead of Invoke() for most methods unless I need to wait for a control to update.
I don't know if this makes sense but I'm trying to figure out how to make the bug happen every time I close the form, so that if its resolved by using BeginInvoke I'm sure its gone. My code to close the port is
private void closeDevicePort()
{
if (devicePort != null)
{
try
{
setMode("D0");
toggleAllBtns();
devicePort.Close();
devicePort = null; //sometimes doesn't get past here
Console.WriteLine("closing++++ here");
}
catch (Exception ex) {
Console.WriteLine(ex);
}
//devicePort = null;
}
}
which gets called through a GUIForm_FormClosed event on FormClosed. How do I make this happen every time to test that changing to BeginInvoke() actually works for my winforms app?
Also here is my DataReceivedHandler where I set the devicePort (which I didn't think was making anything explicitly multi-threaded)
private void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e)
{
SerialPort serialPort1 = (SerialPort)sender;
if (serialPort1.IsOpen)
{
try
{
string message = serialPort1.ReadLine();
if (devicePort == null)
{
devicePort = serialPort1;
}
}catch(Exception ex)
{
Console.WriteLine(ex);
}
}
}
I have a plotData() function which plots data in realtime. Is using BeginInvoke() instead of Invoke() fine here too?
private void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e)
{
SerialPort serialPort1 = (SerialPort)sender;
if (serialPort1.IsOpen)
{
try
{
string message = serialPort1.ReadLine();
Console.WriteLine(message);
if (message.Substring(0, 1) == "!")
{
oldTime = newTime;
//checkPortsTimer.Stop();
//checkPortsTimer.Interval = 1500;
//checkPortsTimer.Start();
}
string flag = message.Substring(1, 1);
string command = message.Substring(2, 1);
string package = message.Substring(3);
switch (flag)
{
case "S":
switch (command)
{
case "C": //ready mode
setMode("SC");
if (devicePort == null)
{
addDevicePort(serialPort1);
}
break;
}
break;
case "D": //data stream
float[] data = Array.ConvertAll(package.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries), float.Parse);
txtData_Update(data);
plotData(data);
break;
default:
Console.WriteLine("not a recognised command. Try Again");
break;
}
}
catch (Exception ex)
{
Console.WriteLine("in data received exception handler");
Console.WriteLine(ex);
}
}
}

Closing a USB serial port leaves the port unavailable

My app uses USB based serial ports to connect to physical hardware devices. I can open any valid USB port and communicate with the external devices. However, when I close the connection, the USB port is left in some sort of indeterminate state for some time, and during that time further attempts to reconnect result in the "Access to port "COM--" is denied" error. However, after some few seconds, attempting to reconnect is successful. How can I determine WHEN the USB port will again support a new connection?
The code looks like this:
private void Setup(string Port)
{
bool ValidPort = false;
int CloseSleep = 10;
_PortName = Port;
_PortType = this;
string[] AvailablePorts = SerialPort.GetPortNames();
foreach(string aPort in AvailablePorts)
{
if (aPort == _PortName)
{
// The required port is listed in the list of available ports)
ValidPort = true;
break;
}
}
if (ValidPort)
{
try
{
if (_ThePort != null)
{
_ThePort.Close();
_ThePort.DataReceived -= ReceivedDataEventHandler;
while(CloseSleep-- > 0)
System.Threading.Thread.Sleep(100);
_ThePort.Dispose();
_ThePort = null;
}
}
catch (Exception ex)
{
EMS_Config_Tool.ModalDialog md = new EMS_Config_Tool.ModalDialog("Closing Port: " + ex.Message, "System Exception");
md.ShowDialog();
}
System.IO.Ports.SerialPort TheNewPort = new System.IO.Ports.SerialPort(Port, 38400);
// Setup the event handlers from Tx and Rx
Handler.DataOutEvent += CommsSender;
TheNewPort.DataReceived += ReceivedDataEventHandler;
TheNewPort.DataBits = 8;
TheNewPort.Parity = Parity.None;
TheNewPort.Handshake = System.IO.Ports.Handshake.None;
TheNewPort.StopBits = System.IO.Ports.StopBits.One;
// We will try 3 times to open the port, and report an error if we fail to open the port
try
{
TheNewPort.Open();
}
catch (Exception)
{
System.Threading.Thread.Sleep(1000);
try
{
TheNewPort.Open();
}
catch (Exception)
{
System.Threading.Thread.Sleep(1000);
try
{
TheNewPort.Open();
}
catch (Exception ex)
{
EMS_Config_Tool.ModalDialog md = new EMS_Config_Tool.ModalDialog("Opening Port: " + ex.Message, "System Exception");
return;
}
}
}
The final catch statement is where the error about Access being denied is issued. Note my attempt to retry opening the port 3 times doesn't really help. If I leave the port alone for about 5 to 10 seconds and retry calling the Setup method it succeeds immediately.

As #Neil said, there are many issues. The best thing to do, in my point of view, is to put the search in a loop, and as soon as the port can be opened, it will be.
I used to do like this :
public Task WaitingPort()
{
while (port is null)
{
port = CheckPort();
}
}
private SerialPort CheckPort()
{
string[] listPort = SerialPort.GetPortNames();
foreach(string namePort in listPort)
{
SerialPort port = new SerialPort(namePort, 9600);
if (!port.IsOpen)
{
try
{
port.Open();
port.ReadTimeout = 1500;
string data = port.Readline();
// I programmed my device to send an "A" until it receives
// "777" to be able to recognize it once opened
if (data.Substring(0, 1) == "A")
{
port.ReadTimeout = 200;
port.Write("777"); // to make it stop sending "A"
return port;
}
else
{
port.Close();
}
}
catch (Exception e1)
{
port.Close();
}
}
}
return null;
}
Of course, this is just some kind of a template which you have to reshape to your use

I have amended my code to use a constrained loop to give it a better chance to work, which it usually does. I was hoping that there was a better way to do it, as I tend to have pretty impatient users who will be posting defect reports if they have to wait 5 or 10 seconds to make a connection....
// We will try several times to open the port, upto 10 times over 5 seconds, and report an error if we finally fail to open the port
try
{
TheNewPort.Open();
}
catch (Exception ex)
{
RetryOpenTimer.Interval = 500;
RetryCount = 10;
RetryOpenTimer.Elapsed += new System.Timers.ElapsedEventHandler(RetryOpenTimer_Elapsed);
WaitForOpen = true;
RetryOpenTimer.Start();
while (WaitForOpen && RetryCount > 0)
{
System.Threading.Thread.Sleep(500);
}
if (WaitForOpen)
{
EMS_Config_Tool.ModalDialog md = new EMS_Config_Tool.ModalDialog("Opening Port: " + ex.Message, "System Exception");
return;
}
}
...
void RetryOpenTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
RetryOpenTimer.Stop();
RetryOpenTimer.Elapsed -= RetryOpenTimer_Elapsed;
try
{
if (RetryCount-- > 0)
{
TheNewPort.Open();
WaitForOpen = false;
}
else
return;
}
catch (Exception)
{
RetryOpenTimer.Start();
RetryOpenTimer.Elapsed += RetryOpenTimer_Elapsed;
}
}

NetMQ Polling a rep socket with a timeout in a loop

I'm trying to port my code from an obsolete library called CastleMQ to NetMQ but I'm running into some problems.
I prefer to using polling with a timeout, for reliability - I just found that it worked best for me from trial and error compared to just sitting blocking the port indefinitely.
here is my CastleMQ code
public int ZeroPort;
private void ThreadProc()
{
var ctx = new Context();
try {
using (var repSocket = ctx.CreateSocket(SocketType.Rep))
{
string bindAddress = "tcp://*:"+ZeroPort;
repSocket.Bind(bindAddress);
print2("*** BINDING on {0} ***", bindAddress);
bool quit = false;
while (!quit) {
try {
var polling = new Polling(PollingEvents.RecvReady, repSocket);
polling.RecvReady += (socket) =>
{ // using socket.Recv() here is guaranted to return stuff
var msg = socket.Recv();
var msgStr = Encoding.UTF8.GetString(msg);
print2("[REP:{0}] {1}", bindAddress, msgStr);
switch (msgStr) {
case "positions": {
StringBuilder csv = new StringBuilder();
print2("csv: {0}", csv.ToString());
socket.Send(csv.ToString());
break;
}
default: {
socket.Send("Unrecognized Command: " + msgStr);
break;
}
}
};
polling.Poll(POLL_TIMEOUT_MS); // this returns once some socket event happens
} catch (Exception e) {
if (e is ThreadAbortException) {
quit = true;
print2("\n*** EXITED ***");
} else print2(e.ToString());
}
}
}
} catch (Exception e) {
print2(e.ToString());
} finally {
ctx.Dispose();
}
}
here is what I tried to do and then got lost with NetMQ
private void ThreadProc()
{
try {
string bindAddress = "#tcp://*:" + ZeroPort;
print2("*** BINDING on {0} ***", bindAddress);
using (var repSocket = new ResponseSocket(bindAddress))
using (var poller = new NetMQPoller { repSocket })
{
// bool quit = false;
// while (!quit)
// these event will be raised by the Poller
repSocket.ReceiveReady += (s, a) =>
{
// receive won't block as a message is ready
string msg = a.Socket.ReceiveString(); // defeinition for ReceiveString() can't be found
// send a response
a.Socket.Send("Response"); // it doesn't like "Response", do I need to wrap it in some object?
I'm especially confused as how to add a timeout so I can poll with a timeout in a loop the way my CastleMQ code does.
Any pointers would be much appreciated, thanks

C# Sockets: 2nd (and more) users can't connect

I connect to my (C#) server and from an App built in Corona SDK but for the second person can never connect.
I have tried using different IP's i.e. two cellphones with external IP's with no difference.
This is how my server listener works:
server.cs
void Listener()
{
while (isRunning)
{
try
{
Socket socket = listener.AcceptSocket();
foreach (var worker in workers)
if (worker.IsAvailable)
{
worker.ProcessNewSocket(socket);
break;
}
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
}
}
}
public void Run()
{
Console.WriteLine("Server.Run()");
listener.Start();
isRunning = true;
foreach (var worker in workers)
{
Thread t = new Thread(worker.Run);
t.Start();
}
Listener();
}
ServerWorker.cs
public void ProcessNewSocket(Socket socket)
{
var pc = new PlayerClient(this);
sockets.Add(socket, pc);
}
// this method will be called in cycle
public void Run()
{
while (server.IsRunning)
{
List<Socket> readList = sockets.Keys.ToList(); //List of sockets that have some data from client available for reading.
List<Socket> writeList = sockets.Keys.ToList(); //List of sockets that are ready to write (send) to the client. An action was made to a table and the change was sent to PlayerClient.Write and is now stored in the queue (MemoreStream)
List<Socket> errorList = sockets.Keys.ToList();
if (readList.Count() != 0 || writeList.Count() != 0 || errorList.Count() != 0)
{
// for providing security you can use System.Net.Security.SslStream here when read/write data,
// see http://msdn.microsoft.com/ru-ru/library/system.net.security.sslstream(v=vs.110).aspx
Socket currentSocket = null;
// foreach socket with events
try
{
foreach (var s in readList)
{
currentSocket = s;
//TODO: Get the actual length of the message.
byte[] data = new byte[2048];
s.Receive(data);
sockets[s].OnData(data);
}
foreach (var s in writeList)
{
currentSocket = s;
if (sockets[s].IsWriteDataAvailable())
{
s.Send(sockets[s].GetWriteBuffer());
sockets[s].ClearWriteBuffer();
}
}
foreach (var s in errorList)
{
//OnError
}
}
// we got exception, depending on the type...
catch (SocketException ex)
{
//Console.WriteLine(ex.ToString());
// send client error message, this is not always possible(for example network failure)
// maybe we would like to notify his opponent about connection failure
// terminate connection
if (ex.ErrorCode == (int)SocketError.ConnectionAborted || ex.ErrorCode == (int)SocketError.ConnectionReset)
RemoveSocket(currentSocket);
else
Console.WriteLine("Other problem .. " + ex.ErrorCode.ToString());
}
}
}
}
I'm new in network programming so I'm not really sure what to do. I have read about using ASync but first I would like to know if there is something I can do with this code and/or if I should change it completely?

I think the "BREAK" statement in your Listener() Block;
foreach (var worker in workers)
if (worker.IsAvailable)
{
worker.ProcessNewSocket(socket);
break; // this BREAK WILL END YOUR loop AFTER first CLIENT FOUND.
}
So, try removing break as;
foreach (var worker in workers)
{
if (worker.IsAvailable)
{
worker.ProcessNewSocket(socket);
}
}

Windows Service: The calling thread cannot access this object because a different thread owns it

Trying to convert XML files using XSL and printing the output. However, receiving the following message: The calling thread cannot access this object because a different thread owns it.
To set an interval for checking files, added a timer to the OnStart.
if (findPrinter() > 0)
{
System.Timers.Timer printNetterCheck = new System.Timers.Timer();
printNetterCheck.Elapsed += new ElapsedEventHandler(OnTimedEvent);
printNetterCheck.Interval = 30000;
printNetterCheck.Enabled = true;
}
The OnTimedEvent:
private void OnTimedEvent(object source, ElapsedEventArgs e)
{
getFiles();
}
If any files available, call print:
foreach (string file in files)
{
try
{
StringWriter xslTransformResult = new StringWriter();
XslCompiledTransform xslt = new XslCompiledTransform();
xslt.Load(xslPath);
xslt.Transform(file, null, xslTransformResult);
if (print(xslTransformResult) == 1)
{
//do some things
The print function:
private int print(StringWriter transformedXML)
{
//assume OK
int rc = 1;
try
{
StringReader printNetterStreamReader = new StringReader(transformedXML.ToString());
PrintSystemJobInfo printNetterJob = printer.AddJob("PrintNetterPrint");
Stream printNetterStream = printNetterJob.JobStream;
Byte[] printNetterByteBuffer = UnicodeEncoding.Unicode.GetBytes(printNetterStreamReader.ReadToEnd());
printNetterStream.Write(printNetterByteBuffer, 0, printNetterByteBuffer.Length);
printNetterStream.Close();
}
catch (Exception e)
{
//return fail
rc = -1;
eventLog.WriteEntry("Error printing: " + e.Message, EventLogEntryType.Error);
}
return rc;
}
When calling print I receive the thread error. Found some stuff about Dispatchers etc.. but those are not available when using services.

Check PrintQueue.AddJob.
The method makes a COM call which requires the application be running in a single apartment (STA). The easiest way to fix that is to add STAThreadAttribute to Main which will force the application to run in a single thread. If you need multithreading in your application then you will need to implement the necessary plumbing to run the PrintQueue separately on an STA Thread.
// Create a factory to hold your printer configuration
// So that it can be retrieved on demand
// You might need to move the findPrinter() logic
public class PrintQueueFactory
{
private static PrintQueue _instance = new PrinterQueue(/* Details */);
public static PrintQueue PrintQueue { get { return _instance; } }
}
private int print(StringWriter transformedXML)
{
//assume OK
int rc = 1;
try
{
var printer = PrintQueueFactory.PrintQueue;
var staThread = new Thread(() => Print(printer, transformedXML.ToString()));
staThread.SetApartmentState(ApartmentState.STA);
staThread.Start();
staThread.Join();
}
catch (Exception e)
{
//return fail
rc = -1;
eventLog.WriteEntry("Error printing: " + e.Message, EventLogEntryType.Error);
}
return rc;
}
private static void Print(PrintQueue printer, string lines)
{
using(var printNetterJob = printer.AddJob("PrintNetterPrint"))
using(var printNetterStreamReader = new StringReader(lines))
using(var printNetterStream = printNetterJob.JobStream)
{
Byte[] printNetterByteBuffer = UnicodeEncoding.Unicode.GetBytes(printNetterStreamReader.ReadToEnd());
printNetterStream.Write(printNetterByteBuffer, 0, printNetterByteBuffer.Length);
}
}

maybe, as you are using a Timer control, it is related with multi-threading, maybe you should check if an Invoke is Required (InvokeRequired) in the Timer.Elapsed event handler.
If so, you should create a delegate to call this function, so it can be executed in the right thread.
Check this Invoke-Required question