Threading Model for a Game Engine

Question

I'm interested in getting threading into the small engine I'm working on in my spare time, but I'm curious over what the best approuch is. I'm curious about the recommended way to sync the physics thread with the rest of the engine, similar to ThisGuy. I'm working with the Bullet Physics SDK, which already use the data copy method he was describing, but I was wondering, once bullet goes through one simulation then syncs the data back to the other threads, won't it result in something like vertical sync, where the rendering thread, half way through processing data suddenly starts using a newer and different set of information?

Is this something which the viewer will be able to notice? What if an explosion of some sort appears with the object that is meant to be destroyed?

If this is an issue, what is then is the best way to solve it?

Lock the physics thread so it can't do anything until the rendering thread (And basically every other thread) has gone through its frame? That seems like it would waste some CPU time. Or is the preferable method to triple buffer, copy the physics data to a second location, continue the physics simulation then copy that data to the rendering thread once its ready?

What approaches do you guys recommend?

Answer 1

The easiest and probably most used variant is to run physic, render, ai, ... threads in parallel and syncronise them after each of them has finished with a frame/timestep. This is not the fastest solution, but the one with the fewest problems. Writing back the data to the rendering thread while this is running, leads to massive syncronisation problems (e.g. you have to lock each vector/matrix while updating it). To make the paralellisation efficent, you have to minimize the amount of data to syncronize, e.g. only write data to the render thread, that can possible be rendered.

When not synronizing after each frame, you can probably get the effect, that the physic/ai uses all the cpu power producing 60fps, while the renderer only renders 10fps, which in most cases is not, what you want.

A double buffering would also increase performance, but you still need to syncronize your threads. A problem is ai and physic or similar threads, because they possible want modify the same data