Multi threaded game - updating, rendering, and how to split them

Question

From the StackOverflow post (it was recommended I move this):

So, I'm working on a game engine, and I've made pretty good progress. However, my engine is single-threaded, and the advantages of splitting updating and rendering into separate threads sounds like a very good idea.

How should I do this? Single threaded game engines are (conceptually) very easy to make, you have a loop where you update -> render -> sleep -> repeat. However, I can't think of a good way to break updating and rendering apart, especially if I change their update rates (say I go through the update loop 25x a second, and have 60fps for rendering) - what if I begin updating halfway through a render loop, or vice versa?

Answer 1

You're going to want to double/triple buffer any data necessary for rendering that gets altered in the update pass. That way you won't be rendering with something that's been partially changed. The reason you'll probably need to triple buffer is needing 1) the copy you're updating, 2) the last copy you updated fully, and 3) the copy that is currently being used for rendering that you don't want to change.

The hardest part is probably working out the best way to organise your data for this.

Answer 2

This website discusses the problem and has implemented a triple-buffer solution as Roger suggested:

http://blog.slapware.eu/game-engine/programming/multithreaded-renderloop-part1/ http://blog.slapware.eu/game-engine/programming/multithreaded-renderloop-part2/ http://blog.slapware.eu/game-engine/programming/multithreaded-renderloop-part3/ http://blog.slapware.eu/game-engine/programming/multithreaded-renderloop-part4/

It is quiet difficult to implement, but the website has both a source and binary distribution of the implementation if you're interested.