Multithreading with a statically linked dll

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Hi,
I am new to multithreading. I have made a dll using shared dll using MFC program using a tutorial, after it I changed its settings to statically linked so i can used to call its functions in a multithread. Now when I am calling this dll functions from anbother project I am getting an error, the first thread stops working at soon as the second thread is called upon. My functions and thread definitions are as follows, I have compiled and copy the updated version of the dll file in my new project.

C++

  CWinThread      *m_thread;
  CWinThread      *m_thread1;


CdecoderD3D9App *decoder_object_1 = new CdecoderD3D9App(460, 1);
m_thread = AfxBeginThread(MainTread, decoder_object_1);

CdecoderD3D9App *decoder_object_2 = new CdecoderD3D9App(460, 2);
m_thread1 = AfxBeginThread(MainTread1, decoder_object_2);

My functions are as follows for both of the threads,

C++

UINT Ctesting_projectDlg::MainTread(LPVOID pParam)

{
    clock_t t1, t2;
    t1 = clock(); 
    CdecoderD3D9App *decoder_object_1 = (CdecoderD3D9App *)pParam;
    char *video_source = "my_movie.mp4";



    decoder_object_1->InitInstance();

    decoder_object_1->run_program(video_source);


    t2 = clock(); 
    float diff = (((float)t2 - (float)t1) / 1000000.0F ) * 10;


    return 0;
}


UINT Ctesting_projectDlg::MainTread1(LPVOID pParam)

{
    clock_t t1, t2;
    t1 = clock(); 
    CdecoderD3D9App *decoder_object_3 = (CdecoderD3D9App *)pParam;

    char *video_source = "my_movie.m2v";



    decoder_object_3->InitInstance();




    decoder_object_3->run_program(video_source);
    t2 = clock(); 
    float diff = (((float)t2 - (float)t1) / 1000000.0F ) * 10;

    return 0;
}

Now when I am calling this function the second threads kind of exit the first thread as soon as it is called. Does that mean i have to make a new dll project with statically linked items or any other problem ?
Also the dll class is basically a modified version of DecoderD3D9 CUDA example, in which CWinApp inheritance is removed also so now it is just a simple independant class.
My dll file properties are as:

C++

Configuration Type -> Dynamic Library(.dll)
Use of MFC -> Use MFC in a static library
Character set -> Use Multi-Byte Character Set

Posted 10-Sep-13 1:55am

nothan

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Comments

nv3 10-Sep-13 8:19am

Whether your DLL is statically or dynamically linked has nothing to do with its multi-threading behavior. If your decoder object is not thread-safe it doesn't help to put it into a statically linked library. Does this entire thing work as long as you have linked it dynamically -- all other things the same?

nothan 10-Sep-13 8:33am

yeah it works fully if i am running one thread but as soon as i start two threads it is still running only one thread the other one stops working as soon as the second one is being called.

pasztorpisti 10-Sep-13 8:35am

One thing is almost sure: the bug is probably not in the code you have posted.

nothan 10-Sep-13 8:39am

But this is the only code present in my application I am using to call upon. Is it possible that the CUDA dll project is not made correctly ?
But its also multithreaded so it should be able to call multithreads.

pasztorpisti 10-Sep-13 8:44am

This is not the full source code of your program for sure. There can be tons of bugs anywhere else. Also CdecoderD3D9App must support multiple threads, read its documentation about multithreading. Calling functions from threads without reading the documentation of the used functions/classes is a suicide.

nothan 10-Sep-13 8:46am

I am just calling the dll functions from this application and also the dll is available for multithreading debug. I will read the documentation again. Thank you.

pasztorpisti 10-Sep-13 8:51am

You are welcome. BTW, what does this mean: "stops working as soon as the second one is being called". A thread doesn't just stop working. It either doesnt start or finishes, returns or crashes, whatever.... If you debug the program then this should be cleared up.

nothan 10-Sep-13 9:01am

Yes the thread starts and it calls the dll function but as soon as the second thread is called the first one exits and the second one starts working. I rechecked my dll project properties that maybe it was not for multithreaded but it is set for that so maybe CUDA based program is limiting it to only called once per thread.

pasztorpisti 10-Sep-13 9:05am

What do you mean on exit?

nothan 10-Sep-13 9:18am

Ends the thread.. Just stops and the second thread takes over.

pasztorpisti 10-Sep-13 9:51am

So basically you don't know what happens to that thread. Then go and debug it.

nothan 10-Sep-13 9:55am

I am debugging it. My idea was that the dll project was not allowing more than one thread so i google for multithreading and the project is on the same pattern, other than that my calling is right so now i am making couple of multiple dlls to call the code in parallel. thankx

pasztorpisti 10-Sep-13 10:01am

This is probably not DLL related. If the lib is a static lib then the code links against your program exactly the same way as if the source files were in your program. The only difference is that in visual studio you can easily use the same static lib source from many projects easily. Compilation and linking is basically still the same. I would go with static linking first if possible and when the bug is fixed I would try to switch to DLL if needed (only if needed!).

nothan 10-Sep-13 10:45am

ah okay Thanks.

chaau 10-Sep-13 20:11pm

Please check the compiler settings for your dll and the main program. Open project properties, navigate to C/C++->Code Generation. Check what Runtime Library is selected. Should be a Multi-Threaded one

nothan 10-Sep-13 21:12pm

yep I have already checked it twice. Thank you.

The_Inventor 11-Sep-13 6:38am

What kind of system are you using? Single core, dual core, Quad core? 32bit, or 64bit CPU and OS? I have over 85 processes going at any moment in the background, any one process can have more than one tread. IE10 that I am using to access this website and write this comment uses 38 Threads, 77 USER objects, 78 GDI objects, and is using 201,612KB as a private working set of memory.

You calculated a difference in float but don't return it or use it.

mahendren 11-Sep-13 10:25am

Check that the library you are using to play video allows you to play two videos at the same time (especially in a shared dll).

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Multithreading with a statically linked dll

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