Multi-threading strategies? (Modifying a scene in a multi-threaded engine through an Editor)

Question

Hi,

I'm trying to write an editor overtop a multi-threaded game engine. In theory, through the editor, the contents of the scene can be totally changed but I haven't been able to come up with a good way for the engine to cope with the changes. (ie delete an entity while the renderer was drawing it). Additionally, I'm hesitant to write code to manage locks at every instance I use an entity or resource that can be potentially deleted. I imagine there has to be a relatively more elegant solution.

Does anyone have any ideas or strategies I can start looking at?

Thanks!

Answer 1

If memory is not a problem, you can could have a two-stage process, where the changes are done in one model, and then a snapshot is taken for the renderer, this way the renderer would always see a consistent view of the model.

Answer 2

In addition to the two-stage process suggested by @lassevk you could use a Pipe structure to "push" commands to the renderer so that these changes gets the form of another work item for the render engine.

For example, say your engine follows a workflow like:

1. Calculate positions
2. Process Physics
3. Process Lights Process Cameras
4. Render Scene

You could just add a new item to the workflow in the position 0, called Process Changes which pulls out the information from the Pipe and incorporates it to the scene.

Answer 3

Without knowing your exact need, it is hard for me to comment on the details, but i think if a combination of copy-on-write and lock-free data structure may help.

When you're rendering, you need read only access, so there are no problems. When you're editing, say deleting an object from a group of objects, you mark the current object "deleted" using atomic operations and your renderer can skip or remove the object before the next render loop. When an object is changed, you make a copy and change the copy and "commit" the change using lock-free techniques.