VB and C++ dll
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Hi I created very simple dll (vc++) which has three functions (start, stop and initialization). it starts capturing sound from soundblaster and when the buffer is filled with the data, dll calls VB calback function (passed with initialization) and passes the buffer size (integer type). First I have some problems with __stdcall declaration in VC dll, but I think I solved that problem. Callback function runs in separated thread under main dll thread. Declaration of initialization of callback function looks like this: __declspec(dllexport) int __stdcall RecToR_Init_Cap(void (__stdcall *tmp)(int_4 size)); IN VB: Public Delegate Sub Callback(ByVal size As Int32) Public Declare Function RecToR_Init_Cap Lib "RecToR_Cap_TR.dll" (ByVal CalBckFunc As Callback) As Int32 "Private Sub Button1_Click" event in VB: Dim cb As Callback cb = AddressOf CallBackFunc Success = RecToR_Init_Cap(cb) Public Sub CallBackFunc(ByVal size As Int32) TextBox1.Text = size & vbCrLf End Sub When I run the application, the callback function is called 50 times and then the application crashes: "An unhandled exception of type 'System.Runtime.InteropServices.SEHException' occurred in Unknown Module. Additional information: External component has thrown an exception. An exception 'System.NullReferenceException' has occured in..." I think I override stack pointer. How can I trace down the problem? From Microsoft articles I get information that I cannot call callbacks from spawned threads within my DLL. Is it possible to overcome this problem? Thanks for any idea Tomaz Rotovnik
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Hi I created very simple dll (vc++) which has three functions (start, stop and initialization). it starts capturing sound from soundblaster and when the buffer is filled with the data, dll calls VB calback function (passed with initialization) and passes the buffer size (integer type). First I have some problems with __stdcall declaration in VC dll, but I think I solved that problem. Callback function runs in separated thread under main dll thread. Declaration of initialization of callback function looks like this: __declspec(dllexport) int __stdcall RecToR_Init_Cap(void (__stdcall *tmp)(int_4 size)); IN VB: Public Delegate Sub Callback(ByVal size As Int32) Public Declare Function RecToR_Init_Cap Lib "RecToR_Cap_TR.dll" (ByVal CalBckFunc As Callback) As Int32 "Private Sub Button1_Click" event in VB: Dim cb As Callback cb = AddressOf CallBackFunc Success = RecToR_Init_Cap(cb) Public Sub CallBackFunc(ByVal size As Int32) TextBox1.Text = size & vbCrLf End Sub When I run the application, the callback function is called 50 times and then the application crashes: "An unhandled exception of type 'System.Runtime.InteropServices.SEHException' occurred in Unknown Module. Additional information: External component has thrown an exception. An exception 'System.NullReferenceException' has occured in..." I think I override stack pointer. How can I trace down the problem? From Microsoft articles I get information that I cannot call callbacks from spawned threads within my DLL. Is it possible to overcome this problem? Thanks for any idea Tomaz Rotovnik
Could be the garbage collector. Try to put this code when you want to stop recording.
GC.KeepAlive(cb)I had the same problem with callback function when capturing video. -
Could be the garbage collector. Try to put this code when you want to stop recording.
GC.KeepAlive(cb)I had the same problem with callback function when capturing video.Hi When the callback function is trigered 50 times I still capturing the sound. I didn't stop sound capturing. Do I need to call GC.KeepAlive(cb) inside the callback function? Tomaz Rotovnik
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Hi When the callback function is trigered 50 times I still capturing the sound. I didn't stop sound capturing. Do I need to call GC.KeepAlive(cb) inside the callback function? Tomaz Rotovnik
The statement
GC.KeepAliveis a way to keep a reference to an object. When the garbage collector "scans" your code, and there isn’t a further reference to an object, it removes it. E.g. the reference to your callback function is lost. In your code…. When the recording is finished, you should callGC.KeepAlive(cb)That way you will not loose your reference. -
The statement
GC.KeepAliveis a way to keep a reference to an object. When the garbage collector "scans" your code, and there isn’t a further reference to an object, it removes it. E.g. the reference to your callback function is lost. In your code…. When the recording is finished, you should callGC.KeepAlive(cb)That way you will not loose your reference.OK Now I understand. Unfortunately dll is still capturing when the error arrise (I didn't call stop function at all) Tomaz Rotovnik