How do I code for dual core?

Two approaches: Use threads, or split up the task into several processes.

Interprocess communication, alright. How do I set the processor affinity for each of the processes inside the code?

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Read here on cooperative multithreading and other forms of multithreaded programming

xtra krazzy said:

Interprocess communication, alright. How do I set the processor affinity for each of the processes inside the code?

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You realize that Windows automatically splits thread onto different processors, yes? If you have two threads, they'll run on both processors.

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xtra krazzy said:

Alas, it seldom works... I found that most of the stress is on the second processor, and the profiler didn't have any stress on the things which were meant to run on one processor.

If this is correct, then my processor is a gimp(one works faster and the other slower) (I ran the same pressure tests on both processors, together).
EDIT: It might be because of the stress which was on the processor beforehand.

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Windows will try to balance threads on each processor. But it will also try to split threads from the same application on different processors (so that if an app has two threads, both threads won't run on the same processor). But remember: though Windows may split the threads, it won't split the processor load. In other words, you can run demanding code in one thread and easy code in one. Of course the processor which runs the demanding thread will get more load - this is normal. Windows will only split the threads - it's up to you to split the load in the threads.

So let me get this straight: In Windows, the first two threads which fork from the main thread go to different cores by default, and the sub-threads of the two threads each go to the same core?

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I'm not 100% sure, but I don't think Windows cares what thread spawned what - they'll still be split onto different processors as Windows sees fit.

If so, how, in Windows terms of functions, can I synchronize two threads in other ways than waiting for a thread to finish? (semaphores in Windows?)

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There are many synchronization functions, but one that you might benefit on is the ability to create and set events. Use CreateEvent to create an event, then use SetEvent and ResetEvent to set or reset the event respectively. You can then use WaitForSingleObject (or WaitForMultipleObjects) to wait to when the event is set. One thread can then wait until another thread sets this event signaling that it is done with whatever the first thread should wait for. Do you get me? There's plenty information about this on the web if you need to know more.

xtra krazzy said:

So there's no actual guarantee that the code will run with a certain affinity, but the probability of having the program's threads run simultaneously is high enough. I guess that sums it up. Thank you very much.

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The scheduler will try to balance processes/threads between the available cpus, yes. I am not certain whether playing with the processor affinity is really needed except in special cases.

When you only have 2 heavy threads in your program, at least it doesn't hurt to set affinity on them, and it is useful because then you can see exactly how much cpu power each one uses just by looking at the cpu monitor in task manager

Of course, if you have a quad core and want to run two programs simultaneously that both hog cpu #1 and cpu #2, then you are in trouble

So I'd recommend to only set affinities during development.