I have been working on creating a multithreaded game engine in my spare time and I currently trying to decide the best way to work an entity sytem into what I have already created. So far, I have used this article from Intel for a starting point for my engine. Thus far I have implemented the normal game loop using tasks, and I am now moving on to getting some of the systems and/or entity-systems incorporated. I have used something similar to Artemis in the past, but the parallelism is throwing me off.
The article from Intel seems to advocate having multiple copies of entity data, and a having changes made to each entity internally being distributed at the end of a complete update. This means that rendering will always be one frame behind, but that seems like an acceptable compromise given the performance benefits that should be gained. When it comes to an entity system like Artemis, though, having each entity being duplicated for each system means that each component will also need to be duplicated. This is doable but to me it seems like it would use up a lot of memory. The portions of the Intel document that discus this are 2.2 and 3.2.2 mainly. I have done some searching to see if I could find any good references for integrating the architectures I am going for, but I have not yet been able to turn up anything useful.
Note: I am using C++11 for this project, but I imagine most of what I am asking should be pretty language agnostic.
Have a global EntityManager that is used for creating and managing Entities and EntityAttributes. Allow read access to them only during the update phase, and store all changes in a queue per thread. Once all tasks are completed the queues are combined and the changes in each are applied. This would possibly have problems with multiple writes to the same fields but I am sure there could be a priority system or timestamp to sort that out. This seems like a good approach to me because systems can be notified of changes to entities pretty naturally during the change distribution stage.
I am looking for some feedback on my solution to see if it even makes sense. I won't lie and claim to be an expert on multithreading, and I am doing this largely for practice. I can forsee some complicated messes rising from my solution where multiple systems are reading/writing multiple values. The change queue I mentioned could also be hard to format in a way that any possible change could easily be communicated when I am not working with POD.
Any feedback/advice would be much appreciated! Thanks!
- http://www.gamedev.net/topic/560083-rendering-in-a-task-based-multithreaded-environment/ (not mentioned in post this post but similar solution mentioned)