I think we'd have to take a harder look at the C library before implementing Sync. I think Send is probably fine, but it's not actually even totally clear that Send is fair because the run-time initialization of the LED strip arrays in the ws2811_t structs could end up putting references to the same region of memory in those structs.

Update: Reading a little more about the Sync trait in particular, I think that is viable, but I still don't know about Send for the Controller struct itself.

I'm taking another look at it, and in its current state Sync is not safe to implement because Controller also implements Clone - that would lead to pointer aliasing. Would it be possible to remove the Clone impl?

Yeah I can't come up with a good reason it should implement Clone, however, I also don't have a great reason to believe it should implement Sync.