[SOLVED] System.AccessViolationException When Calling Dll Function Again
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The problem was in the unmanaged DLL. But I really learnt a great deal about other topics such as BackgroundWorkers and TPL. Thanks all. ======================= Hello There. I have this small DLL that takes
input_nameandoutput_nameas parameters. It opens the input file, reads it and produces output file with the specified name after some processing. I then call this function from C#. First time I call it, it runs fine. But second time around, it throws this exceptionAn unhandled exception of System.AccessViolationException occured in CSharpProgram.exe. Attempted to read or write protected memory.Here is what I am trying.[DllImport("MyDll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int Call_Dll_Main(string input, string output);private void Button_Click(object sender, EventArgs ea)
{
new System.Threading.Thread(new System.Threading.ThreadStart(Call_Dll_Function)).Start()
}private void Call_Dll_Function()
{
int nResult = Call_Dll_Main(txtInputFile.Text.Trim(), txtOutputFile.Text.Trim()); // HERE EXCEPTION COMES...FIRST TIME FINE...IT COMES SECOND TIME I CLICK THE BUTTON
}What could be wrong? What am I missing here? Thanks for any input.
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The problem was in the unmanaged DLL. But I really learnt a great deal about other topics such as BackgroundWorkers and TPL. Thanks all. ======================= Hello There. I have this small DLL that takes
input_nameandoutput_nameas parameters. It opens the input file, reads it and produces output file with the specified name after some processing. I then call this function from C#. First time I call it, it runs fine. But second time around, it throws this exceptionAn unhandled exception of System.AccessViolationException occured in CSharpProgram.exe. Attempted to read or write protected memory.Here is what I am trying.[DllImport("MyDll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int Call_Dll_Main(string input, string output);private void Button_Click(object sender, EventArgs ea)
{
new System.Threading.Thread(new System.Threading.ThreadStart(Call_Dll_Function)).Start()
}private void Call_Dll_Function()
{
int nResult = Call_Dll_Main(txtInputFile.Text.Trim(), txtOutputFile.Text.Trim()); // HERE EXCEPTION COMES...FIRST TIME FINE...IT COMES SECOND TIME I CLICK THE BUTTON
}What could be wrong? What am I missing here? Thanks for any input.
Well, the first thing I would do is put those TextBox values you trim into variables before you pass them to the .DLL. The GC will collect those values since they don't have any managed variables or pins holding onto references to them so the GC may be collecting them before your DLL code is finished with them. Next, it would appear that you're completely ignoring the return code from the C function. I t has nothing to do with the error, but it's something to watch out for. Any other problems would be in the C code itself, which you didn't show for this function.
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Dave Kreskowiak -
The problem was in the unmanaged DLL. But I really learnt a great deal about other topics such as BackgroundWorkers and TPL. Thanks all. ======================= Hello There. I have this small DLL that takes
input_nameandoutput_nameas parameters. It opens the input file, reads it and produces output file with the specified name after some processing. I then call this function from C#. First time I call it, it runs fine. But second time around, it throws this exceptionAn unhandled exception of System.AccessViolationException occured in CSharpProgram.exe. Attempted to read or write protected memory.Here is what I am trying.[DllImport("MyDll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int Call_Dll_Main(string input, string output);private void Button_Click(object sender, EventArgs ea)
{
new System.Threading.Thread(new System.Threading.ThreadStart(Call_Dll_Function)).Start()
}private void Call_Dll_Function()
{
int nResult = Call_Dll_Main(txtInputFile.Text.Trim(), txtOutputFile.Text.Trim()); // HERE EXCEPTION COMES...FIRST TIME FINE...IT COMES SECOND TIME I CLICK THE BUTTON
}What could be wrong? What am I missing here? Thanks for any input.
Hi, I'm assuming you are using WinForms and those textXXXFile objects are Controls, maybe TextBoxes. A Control should only be created and used by a single thread, most often that would be the main or "GUI thread"; violating this rule is bound to give you AccessViolation trouble. I would recommend you use one (or more if you think you must) BackgroundWorker objects ibstead of bare Threads. A BGW will execute most of its task on a separate thread (which it borrows from the ThreadPool), however it also offers progress and completion events which execute on the main thread (assuming you created the BGW on the main thread) so all AccessViolations would disappear. If you're unfamiliar with the BGW class, read up on it, I'm pretty sure CP has some fine articles about it. Note 1: you should get the inputfile before entering the DoWork event. Note 2: you could reuse the BGW object, or create a new one, that is up to you. Note 3: there are some BGW properties you have to set true explicitly for it to activate all its goodies! good luck :)
Luc Pattyn [My Articles] Nil Volentibus Arduum
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The problem was in the unmanaged DLL. But I really learnt a great deal about other topics such as BackgroundWorkers and TPL. Thanks all. ======================= Hello There. I have this small DLL that takes
input_nameandoutput_nameas parameters. It opens the input file, reads it and produces output file with the specified name after some processing. I then call this function from C#. First time I call it, it runs fine. But second time around, it throws this exceptionAn unhandled exception of System.AccessViolationException occured in CSharpProgram.exe. Attempted to read or write protected memory.Here is what I am trying.[DllImport("MyDll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int Call_Dll_Main(string input, string output);private void Button_Click(object sender, EventArgs ea)
{
new System.Threading.Thread(new System.Threading.ThreadStart(Call_Dll_Function)).Start()
}private void Call_Dll_Function()
{
int nResult = Call_Dll_Main(txtInputFile.Text.Trim(), txtOutputFile.Text.Trim()); // HERE EXCEPTION COMES...FIRST TIME FINE...IT COMES SECOND TIME I CLICK THE BUTTON
}What could be wrong? What am I missing here? Thanks for any input.
pass the textbox values as parameters to Call_Dll_Function(). Remember that your thread can't access the controls from the UI thread - can't cross the streams. I personally would use the Task Parallel Library (TPL) for this. There are articles on this here at Codeproject. Check it out (Sacha Barber has some good ones). I use TPL often. Task Parallel Library: 1 of n[^]
private void Call_Dll_Function(string input, string output)
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The problem was in the unmanaged DLL. But I really learnt a great deal about other topics such as BackgroundWorkers and TPL. Thanks all. ======================= Hello There. I have this small DLL that takes
input_nameandoutput_nameas parameters. It opens the input file, reads it and produces output file with the specified name after some processing. I then call this function from C#. First time I call it, it runs fine. But second time around, it throws this exceptionAn unhandled exception of System.AccessViolationException occured in CSharpProgram.exe. Attempted to read or write protected memory.Here is what I am trying.[DllImport("MyDll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int Call_Dll_Main(string input, string output);private void Button_Click(object sender, EventArgs ea)
{
new System.Threading.Thread(new System.Threading.ThreadStart(Call_Dll_Function)).Start()
}private void Call_Dll_Function()
{
int nResult = Call_Dll_Main(txtInputFile.Text.Trim(), txtOutputFile.Text.Trim()); // HERE EXCEPTION COMES...FIRST TIME FINE...IT COMES SECOND TIME I CLICK THE BUTTON
}What could be wrong? What am I missing here? Thanks for any input.
Such Access Violation Exceptions often mean that a pointer pointed to some location which is outside of the process space of your program. And such things are more likely to happen in unmanaged code, i.e. the C dll. As we do not see the code of that dll, we can only speculate. It could be possible that the code tries to do something at the memory location of the strings it was passed at the first call, but Garbage Collection has removed them meanwhile.
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Hi, I'm assuming you are using WinForms and those textXXXFile objects are Controls, maybe TextBoxes. A Control should only be created and used by a single thread, most often that would be the main or "GUI thread"; violating this rule is bound to give you AccessViolation trouble. I would recommend you use one (or more if you think you must) BackgroundWorker objects ibstead of bare Threads. A BGW will execute most of its task on a separate thread (which it borrows from the ThreadPool), however it also offers progress and completion events which execute on the main thread (assuming you created the BGW on the main thread) so all AccessViolations would disappear. If you're unfamiliar with the BGW class, read up on it, I'm pretty sure CP has some fine articles about it. Note 1: you should get the inputfile before entering the DoWork event. Note 2: you could reuse the BGW object, or create a new one, that is up to you. Note 3: there are some BGW properties you have to set true explicitly for it to activate all its goodies! good luck :)
Luc Pattyn [My Articles] Nil Volentibus Arduum
Accessing a control from a different thread results in an
InvalidOperationException, e.g.Quote:
Cross-thread operation not valid: Control 'button1' accessed from a thread other than the thread it was created on.
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The problem was in the unmanaged DLL. But I really learnt a great deal about other topics such as BackgroundWorkers and TPL. Thanks all. ======================= Hello There. I have this small DLL that takes
input_nameandoutput_nameas parameters. It opens the input file, reads it and produces output file with the specified name after some processing. I then call this function from C#. First time I call it, it runs fine. But second time around, it throws this exceptionAn unhandled exception of System.AccessViolationException occured in CSharpProgram.exe. Attempted to read or write protected memory.Here is what I am trying.[DllImport("MyDll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int Call_Dll_Main(string input, string output);private void Button_Click(object sender, EventArgs ea)
{
new System.Threading.Thread(new System.Threading.ThreadStart(Call_Dll_Function)).Start()
}private void Call_Dll_Function()
{
int nResult = Call_Dll_Main(txtInputFile.Text.Trim(), txtOutputFile.Text.Trim()); // HERE EXCEPTION COMES...FIRST TIME FINE...IT COMES SECOND TIME I CLICK THE BUTTON
}What could be wrong? What am I missing here? Thanks for any input.
Hello May I consult you how did u solved this problem? I have the similar problem [UnmanagedFunctionPointer(CallingConvention.StdCall)] private delegate bool _B_B(byte O1, byte O2, byte O3, byte O4, byte O5); private IntPtr hMod; private _B_B funA; if (chk = (hMod = LoadLibrary("my.dll")) != IntPtr.Zero) if (chk = (pFunc = GetProcAddress(hMod, "funA")) != IntPtr.Zero) funA = (_B_B)Marshal.GetDelegateForFunctionPointer(pFunc, typeof(_B_B)); private void button_Click(object sender, EventArgs e) { bool chk = false; byte temp1 = 1, temp2 = 0, temp3 = 15, temp4 = 45, temp5 = 90; try { if (!(chk = funA(temp1, temp2, temp3, temp4, temp5))) MessageBox.Show("set fail!"); } catch (Exception ex) { MessageBox.Show("fail!"); } }
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Hello May I consult you how did u solved this problem? I have the similar problem [UnmanagedFunctionPointer(CallingConvention.StdCall)] private delegate bool _B_B(byte O1, byte O2, byte O3, byte O4, byte O5); private IntPtr hMod; private _B_B funA; if (chk = (hMod = LoadLibrary("my.dll")) != IntPtr.Zero) if (chk = (pFunc = GetProcAddress(hMod, "funA")) != IntPtr.Zero) funA = (_B_B)Marshal.GetDelegateForFunctionPointer(pFunc, typeof(_B_B)); private void button_Click(object sender, EventArgs e) { bool chk = false; byte temp1 = 1, temp2 = 0, temp3 = 15, temp4 = 45, temp5 = 90; try { if (!(chk = funA(temp1, temp2, temp3, temp4, temp5))) MessageBox.Show("set fail!"); } catch (Exception ex) { MessageBox.Show("fail!"); } }
My friend I don't remember what the issue was, but it was certainly in C++ dll. And that is what I updated the original post/question. Please double check C++ dll. Checkout this video tutorial
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The problem was in the unmanaged DLL. But I really learnt a great deal about other topics such as BackgroundWorkers and TPL. Thanks all. ======================= Hello There. I have this small DLL that takes
input_nameandoutput_nameas parameters. It opens the input file, reads it and produces output file with the specified name after some processing. I then call this function from C#. First time I call it, it runs fine. But second time around, it throws this exceptionAn unhandled exception of System.AccessViolationException occured in CSharpProgram.exe. Attempted to read or write protected memory.Here is what I am trying.[DllImport("MyDll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int Call_Dll_Main(string input, string output);private void Button_Click(object sender, EventArgs ea)
{
new System.Threading.Thread(new System.Threading.ThreadStart(Call_Dll_Function)).Start()
}private void Call_Dll_Function()
{
int nResult = Call_Dll_Main(txtInputFile.Text.Trim(), txtOutputFile.Text.Trim()); // HERE EXCEPTION COMES...FIRST TIME FINE...IT COMES SECOND TIME I CLICK THE BUTTON
}What could be wrong? What am I missing here? Thanks for any input.
Hi Django_Untaken did you solve this problem? I have the same problem. Thank in advance