Make rayon optional

[superdump]

In some cases projects have existing threading solutions and do not want/need to also pull in rayon. It would be useful for rayon and the dependencies needed for multi-threaded sorting to be an optional feature.

[nessex]

Understood! I've debated for a while having a purely single-threaded version of this. Out of curiosity, did you try the single-threaded configuration for the benchmarks? I see your numbers for multi-threaded in the linked post. Edit: Yes, you did.

https://github.com/Nessex/rdst#single-threaded-variant

I know this doesn't solve the rayon dependency issue, but I'll see how possible making that optional is in the next few days. Shouldn't be too hard!

[nessex]

@superdump Working on this over here:

#3

[nessex]

Benchmark

I don't know exactly how you got the timings in your original post to give you useful numbers, but here is my machine's bevymark output from around the 1500th frame.

It's a plain old m1 macbook (16GB, 8C/8GPU), so my GPU is probably holding me back a lot.

cargo run --release --example bevymark -- 20000 8

rdst single-threaded

I used your rdst commit

Except I replaced the dependency:

-rdst = "0.19.2"
+rdst = { git = "https://github.com/Nessex/rdst.git", branch = "nessex-multi-threaded-feature", default-features = false }

2022-03-25T12:33:28.383119Z  INFO bevy diagnostic: frame_time                      :    0.066734s (avg 0.065005s)
2022-03-25T12:33:28.383137Z  INFO bevy diagnostic: fps                             :   15.383473  (avg 15.054594)
2022-03-25T12:33:28.383139Z  INFO bevy diagnostic: frame_count                     : 1511.000000  (avg 1511.000000)

bevyengine/bevy master

Upstream master: 28ba87e6c8f48a6b41b6743b748a72d41728523c

2022-03-25T12:45:29.755156Z  INFO bevy diagnostic: frame_time                      :    0.068774s (avg 0.068488s)
2022-03-25T12:45:29.755174Z  INFO bevy diagnostic: fps                             :   14.601051  (avg 14.902787)
2022-03-25T12:45:29.755177Z  INFO bevy diagnostic: frame_count                     : 1504.000000  (avg 1504.000000)

[nessex]

Appreciate the feedback! This is a nice addition. Let me know if there's any part of this idea that I missed 👍