Multi core processor support in CoD

[Heliocon]

Originally Posted by mazex

OK - please calm down. Let me try to explain what I mean then...

Well, I did write a long example with pseudo code and all in my second post in this thread but deleted it as it was to long winded. I realize that you actually think you are right and then naturally think that I'm just talking bull so let's try to sort this out then.

I think that the problem is that you have maybe confused threads and cores in some way. When you write a Windows program it will run in a process and if you do no not create more threads yourself in the code it will just run on a single thread. That thread in it's turn can only run on one CPU or Core (and the OS assigns that if you don't mess with that yourself which really should not be done) . So a game that does not create additional threads will run on one core... It will do calls to the OS that will use other threads for that but generally it will just load one core itself. Then to use the other cores you have to create new threads from your code and start them yourself in the code. The OS can then let them run on one of the other cores or CPU:s if available or chop the time on the CPU between the threads if you have only one CPU/Core. OK - so the threads run in the same process but one of the problems is that if they are going to access shared memory (variables like the state of the me 109 in front of you) they may try to update the same shared memory (like an array of detected enemies that is a private variable in the CFighterPlane object) and that's a no no. Therfore you have to make sure that the thread that is going to update that shared variable get's exclusive access to the variable while updating it - which is essential if you are going to write thread safe code (handled by identifying these critical sections and make sure to exclusive access that memory while updating it so no other thread does that at the same time). The problem is also that both the AI thread (if you create a thread for that in your code and the OS then assigns that thread to run on a core.) and the code for the Collision detection might want to update the number of enemies detected by that specific enemy plane object as the collision detection code has just "killed" that same enemy plane that crashed into a mountain in classic IL2 way The AI code is then on the same time trying to update the object that got "killed" to try to avoid the mountain. What happens then? Those problems are really hard to debug in multi threaded code as opposed to traditional single threaded code that can be debugged line for line but the in the multi threaded code your breakpoint at the part of the code that detected the collision will stop but what is the state of the other thread? Those problems are hard to solve and if your AI thread is milling along updating the "inputs" for the AI planes the render loop has to know that as it updates the actual meshes loaded to the GPU each loop in the main game loop. Not trying to push you down but trying to explain - OK?

/Mazex

Good explanation. I understand what you are saying and it does indeed seem like a plausible problem. The one question though is when you say memory, what are you refering to in the system? Is this cpu cache? It may be harder to program but parallel processing is still faster then serial, even if it may be more difficult to work with (I would argue that its more of an issue with people adjusting to the new "format" and that over time it will become much easier.)
I understand the differance between threads, cores, processes etc

Also the reason I hate programming is debugging because I accidently put a comma or a mistype somewhere and the whole damn thing goes nuts and spams me with errors and I cry into my keyboard as I spend the next day going through 1 hour of code to find the mistake