AccessViolationException occured using P/Invoke with Media Foundation Interface in Multithread application

Question

I'm using the P/Invoke in C# to call native function from C++ DLL as below:

C++ DLL:

    extern "C"
    {
        // Function: Create Wmv video from sequences image. Codec: WMV3 (VC-1)
        __declspec(dllexport) bool __stdcall CreateWMV(...)
        {
        ...
        }
    }

C# wrapper class. I create the C# wrapper class function to map with native C++ code:

    [DllImport("AVIEncoder.dll", EntryPoint = "CreateWMV", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.StdCall)]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static extern bool createWmv(...);

I'm sure that the parameters were marshaling correctly in C#, because it would run successfully when I called directly in client C# code. The issue only occurred when I put the function in background thread.

private void Test()
{
....
createWmv(...); // This call was processed without issue
Thread backgroundThread = new Thread(
    new ThreadStart(()=>
    {
        createWmv(...); // This call causes AccessViolationException
    }
}

The function createWmv() uses the Media Foundation Interface to generate Wmv video. I tried to debug and I found out that when I commented out the function IMFSinkWriter::WriteSample() in native code, the program run without causing the exception.

Thus, I wonder whether Microsoft has something weird in SinkWriter implementation. Does anyone have the same issue using Media Foundation this way?

I think we should look at your C++ code for more details. (It seems like a complex threading issue which has something to do with i.e. Window handles aor thread heap.) — mg30rg, Jun 01 '15 at 08:51
Try setting [ApartmentState to STA](http://stackoverflow.com/a/21488526/706456) — oleksii, Jun 01 '15 at 08:54
@oleksii thanks, It seems to be run with STA ApartmentState now. — Khai Nguyen, Jun 01 '15 at 09:33

score 1 · Accepted Answer · answered Jun 01 '15 at 10:06

Follow oleksii's comment, I set below:

backgroundThread.TrySetApartmentState(ApartmentState.STA); // Add this to fix createWMV() in multithreading
backgroundThread.Name = "CreateVideoThead";
backgroundThread.Start();

Now, the program could run without exception. Thanks for the concept of ApartmentState in C# threading.

AccessViolationException occured using P/Invoke with Media Foundation Interface in Multithread application

1 Answers1