Full duplex operation, functions C++ C# without textbox

Question

Full duplex operation, functions C++ C# without textbox

Noah Aas 1,210

Hello,

https://learn.microsoft.com/en-us/answers/questions/2152915/full-duplex-operation-functions-c-c

I need to send a data string from C# to C++ that isn't in any window (textbox). Is this possible? If so, how?

If I fill the textbox from outside I get error messages. cross-thread exception C# WinForms

How can I best solve this?

Background: I want to send a message from C# to C++ cyclically every 60 seconds.

<IsRunning>
  <Request stillAlive="1" />
</IsRunning>

RLWA32 52,571 Reputation points

2025-04-15T17:56:03.53+00:00

I need to send a data string from C# to C++ that isn't in any window (textbox). Is this possible? If so, how?

OK, If the string is not in a TextBox control then from where are you obtaining it? Regardless, the mechanics of using WM_COPYDATA remain unchanged.

If I fill the textbox from outside I get error messages. cross-thread exception C# WinForms

You are probably attempting to update the control from a thread other than the UI thread. See https://learn.microsoft.com/en-us/dotnet/desktop/winforms/controls/how-to-make-thread-safe-calls-to-windows-forms-controls
Noah Aas 1,210 Reputation points

2025-04-15T18:35:02.5733333+00:00

Hello,

I'm reading a file and want to send it. Instead of a textbox, I'm using a string. I get an exception at 2.

Could it be because it's not a window? No clipboard.
Noah Aas 1,210 Reputation points

2025-04-15T18:37:50.88+00:00

We have the ButtonClick event and read the textbox. How would you read this textbox thread-safely?

And question 2, we have another event, reading the contents of a file and sending it. How would you implement this?
RLWA32 52,571 Reputation points

2025-04-15T19:30:49.49+00:00

Make things easy for us. Share a demo project that reproduces the problems you are having.

Bruce (SqlWork.com) 84,086

again what triggers reading the file? if all calls are made by the windows loop, then there are no issues.

if some async event will cause a call and you need to process the response, then you need to switch to timer to reschedule, and completion routines:

{
    private static int myLock = 0;
    
    // single threaded
    public static void Invoke<T>(Func<T> code, Action<T> completionCode)
    {
        var gotLock = Interlocked.CompareExchange(ref myLock, 1, 0);
        if (gotLock == 0)
        {
            var timer = new System.Timers.Timer();
            timer.Interval = 10;
            timer.AutoReset = false;
            timer.Elapsed += (o,e) => Invoke(code, completionCode);
            timer.Start(); 
            timer.Enabled = true;
        }
        else if (gotLock == 1)
        {
            T rs;
            try { rs = code(); }
            finally { Interlocked.Decrement(ref myLock); }
            completionCode(rs);
        }
        else
        {
            throw new InvalidOperationException("lock out of sync");
        }
    }
}

and called like:


SafeCode.Invoke(() => SendMessage(...), rs => ProcessesResponse(rs));

you could switch to threads and a mutex or the simple lock statement. if the C++ component is not thread safe, then I'd create a background thread that calls the C++ component which uses a queue.

Noah Aas 1,210 Reputation points

2025-04-16T05:40:12.03+00:00

I'm sorry, can you please show the complete code?

SafeCode.Invoke(() => SendMessage(...), rs => ProcessesResponse(rs));

What is SafeCode
Noah Aas 1,210 Reputation points

2025-04-19T06:59:48.9166667+00:00

Make things easy for us. Share a demo project that reproduces the problems you are having.

@RLWA32

I can't post the whole project because it doesn't mine.

Noah Aas 1,210

@RLWA32, Bruce (SqlWork.com), I found out that, if I create a handle in the timer function and pass it, it seems to work. Is the timer thread safe? How can I check that?

IntPtr myHandle = new IntPtr();
myHandle = (IntPtr)(0xFAA1);

 private void TransmitToCpp(string send, IntPtr handle)
 {
     if (m_hWndReceiver != IntPtr.Zero)
     {
	 //..
	 //..
	 IntPtr lParam = Marshal.AllocHGlobal(Marshal.SizeOf(cds));
	Marshal.StructureToPtr(cds, lParam, true);
	var result = SendMessage(m_hWndReceiver, WM_COPYDATA, handle, lParam);
	Marshal.FreeHGlobal(lParam);
	Marshal.FreeHGlobal(cds.lpData);
	if (result == IntPtr.Zero)

RLWA32 52,571 Reputation points

2025-04-19T09:38:29.24+00:00

@Noah Aas,

I can't post the whole project because it doesn't mine.

I asked you to share a demo that reproduces the issue. I'm not asking you to share an entire project/solution.A demo provides context and code that is relevant to the problem at hand. It eliminates anything not relevant and facilitates the debugging process.

And another benefit of creating a demo to reproduce an issue can be finding the solution to the problem.
Noah Aas 1,210 Reputation points

2025-04-21T14:13:14.69+00:00

The basis is your sample project.

Let's continue there, thank you in advance.
https://learn.microsoft.com/en-us/answers/questions/2259458/full-duplex-operation-functions-c-c-windows-proble?comment=question&translated=false#newest-question-comment

Answer accepted by question author

0 additional answers

Your answer

RLWA32 52,571 Reputation points

2025-04-15T17:56:03.53+00:00

I need to send a data string from C# to C++ that isn't in any window (textbox). Is this possible? If so, how?

OK, If the string is not in a TextBox control then from where are you obtaining it? Regardless, the mechanics of using WM_COPYDATA remain unchanged.

If I fill the textbox from outside I get error messages. cross-thread exception C# WinForms

You are probably attempting to update the control from a thread other than the UI thread. See https://learn.microsoft.com/en-us/dotnet/desktop/winforms/controls/how-to-make-thread-safe-calls-to-windows-forms-controls
Noah Aas 1,210 Reputation points

2025-04-15T18:35:02.5733333+00:00

Hello,

I'm reading a file and want to send it. Instead of a textbox, I'm using a string. I get an exception at 2.

Could it be because it's not a window? No clipboard.
Noah Aas 1,210 Reputation points

2025-04-15T18:37:50.88+00:00

We have the ButtonClick event and read the textbox. How would you read this textbox thread-safely?

And question 2, we have another event, reading the contents of a file and sending it. How would you implement this?
RLWA32 52,571 Reputation points

2025-04-15T19:30:49.49+00:00

Make things easy for us. Share a demo project that reproduces the problems you are having.
Bruce (SqlWork.com) 84,086 Reputation points

2025-04-15T20:39:31.7566667+00:00

again what triggers reading the file? if all calls are made by the windows loop, then there are no issues.

if some async event will cause a call and you need to process the response, then you need to switch to timer to reschedule, and completion routines:

{ private static int myLock = 0; // single threaded public static void Invoke<T>(Func<T> code, Action<T> completionCode) { var gotLock = Interlocked.CompareExchange(ref myLock, 1, 0); if (gotLock == 0) { var timer = new System.Timers.Timer(); timer.Interval = 10; timer.AutoReset = false; timer.Elapsed += (o,e) => Invoke(code, completionCode); timer.Start(); timer.Enabled = true; } else if (gotLock == 1) { T rs; try { rs = code(); } finally { Interlocked.Decrement(ref myLock); } completionCode(rs); } else { throw new InvalidOperationException("lock out of sync"); } } }

and called like:

SafeCode.Invoke(() => SendMessage(...), rs => ProcessesResponse(rs));

you could switch to threads and a mutex or the simple lock statement. if the C++ component is not thread safe, then I'd create a background thread that calls the C++ component which uses a queue.
Noah Aas 1,210 Reputation points

2025-04-16T05:40:12.03+00:00

I'm sorry, can you please show the complete code?

SafeCode.Invoke(() => SendMessage(...), rs => ProcessesResponse(rs));

What is SafeCode
Noah Aas 1,210 Reputation points

2025-04-19T06:59:48.9166667+00:00

Make things easy for us. Share a demo project that reproduces the problems you are having.

@RLWA32

I can't post the whole project because it doesn't mine.
Noah Aas 1,210 Reputation points

2025-04-19T07:13:37.4766667+00:00

@RLWA32, Bruce (SqlWork.com), I found out that, if I create a handle in the timer function and pass it, it seems to work. Is the timer thread safe? How can I check that?

IntPtr myHandle = new IntPtr(); myHandle = (IntPtr)(0xFAA1); private void TransmitToCpp(string send, IntPtr handle) { if (m_hWndReceiver != IntPtr.Zero) { //.. //.. IntPtr lParam = Marshal.AllocHGlobal(Marshal.SizeOf(cds)); Marshal.StructureToPtr(cds, lParam, true); var result = SendMessage(m_hWndReceiver, WM_COPYDATA, handle, lParam); Marshal.FreeHGlobal(lParam); Marshal.FreeHGlobal(cds.lpData); if (result == IntPtr.Zero)
RLWA32 52,571 Reputation points

2025-04-19T09:38:29.24+00:00

@Noah Aas,

I can't post the whole project because it doesn't mine.

I asked you to share a demo that reproduces the issue. I'm not asking you to share an entire project/solution.A demo provides context and code that is relevant to the problem at hand. It eliminates anything not relevant and facilitates the debugging process.

And another benefit of creating a demo to reproduce an issue can be finding the solution to the problem.
Noah Aas 1,210 Reputation points

2025-04-21T14:13:14.69+00:00

The basis is your sample project.

Let's continue there, thank you in advance.
https://learn.microsoft.com/en-us/answers/questions/2259458/full-duplex-operation-functions-c-c-windows-proble?comment=question&translated=false#newest-question-comment

Answer 1

Bruce (SqlWork.com) 84,086

The timer is thread safe, as you are only using one thread. But a timer interrupts the current thread. So if you use a thread timer, it could fire during a current call. If you use a timer control and windows control events, the events are triggered by the window loop and do not overlap.

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