How to make software run in parallel, c++, directshow, opencv - c++

Question

I've been working on a facetracking system last couple of months and now I need to make everything run in parallel to increase the performance.
The main cpp file is:
int _tmain(int argc, _TCHAR* argv[])
{
cFrame.initCamFrames(20, 1600, 1200, 3); //INITIATES BUFFER FOR CAM FRAMES, 20 frames, res:1600x1200, 3bytes per pixel.
eyeTracking.initTrackingSystem(&cFrame); //INITIATES EYETRACKING SOFTWARE WITH POINTER TO THE BUFFER WHERE EYETRACKINGSOFTWARE GETS THE FRAMES TO SEARCH WITHIN. (opencv)
directShow directShowClass;
directShowClass.initiateDirectShow(false, &cFrame); //INITIATES DIRECTSHOW WITH POINTER TO BUFFER WHERE IT SHOULD SAVE FRAMES FROM CAM
directShowClass.runDirectShow(); //START CAPTURING FRAMES INTO BUFFER
eyeTracking.runTrackingSystem(); //START SEARCH FOR FACE AND EYES.
system("pause");
directShowClass.stopDirectShow();
}
I want "directShowClass.runDirectShow();" and "eyeTracking.runTrackingSystem();" to run in real parallel. now I think that they run as threads in pseudo-parallel. (simple printf in each method occur mixed up in the terminal).
I guess that making a program run in parallel is not that simple as I would like it to be. But I guess that it is possible :D
Please give me some advise where to start searching for information about how to paralellisize.
I have a dual core processor.
Thanks!

Answer 1

Printf is not thread-safe,aka it can mix up buffers like you encountered. You can run the process in pseudo-parallel (like switch each call to another processing step) or run it in hardware-concurrency (std::thread, pthreads, windows thread, boost::thread).
if you have a dual core processor you surely can take advantage of multi-core processing, I would suggest to use boost.

Answer 2

Just to clear out, by using threads you do get real parallelism. But remember that your computer is also running in it's cores other processes in background that occupy CPU time, so your functions are not always being executed.
In order to get some parallelism in C++ you have many options. I name three:
. The oldest most common way is to use the pthread library, which is built in into almost every compiler.
. The new C++ standard, called C++11 includes some native libraries to deal with multi-threading, you can check that out, but it is still not supported by every compiler. And most compilers that support it have only partial functionality. You also need to activate the standard explicitly. For example:
gcc -std=c++11
. Finally, if you are in the mood for some "higher level" stuff, you can put some effort in learning about the OpenMP framework, which uses pragma directives to annotate parallel tasks. The framework will then deal with all the creation of threads, so you can use your time in some other stuff.
P.S: The reason why the output comes out mixed is not because the threads run in pseudo-parallel, but because they are concurrently writting on the buffer. So when the buffer is dumped you see it as the threads wrote it. If any, this is a proof that they are actually running in parallel, but you are making them write their output in the same buffer ;)