Check out pre-built Java native interfaces

[gafter]

@ToddSmall called my attention to http://bytedeco.org/ which provides pre-built Java native interfaces to many popular native libraries. We should check it out and see how valuable it might be to us.

[ToddSmall]

I made a little example of using Bytedeco's pre-built Java native interface for MKL here.

[gafter]

@ToddSmall is proposing to prepare a PR that illustrates the approach for a small subset of our native code. We will need to evaluate whether this will make fbcode integration (and maintenance) more or less difficult. /cc @shannyang

[shannyang]

So I think this shouldn't add any issues to the fbcode integration that we weren't already aware of, but there's some work to do before we can properly add it. Fortunately it's all stuff we have to do anyway:

• I haven't figured out how to make third-party-java work, which is needed for adding any external libraries imported through Kotlin (as opposed to our own handwritten JNIs). Right now there seems to be some sort of dependency version conflict with stdlib, though I don't have much more insight than that. I'll need to figure this out for some of the example visualizations anyway, so Bytedeco probably won't complicate this too much.
• Right now, JNI seems inaccessible from kotlin tests run through Buck (including through indirect dependencies). I'll keep track of this problem in facebookresearch/diffkt.preopen#260 . Again, this is already blocking everything and adding Bytedeco shouldn't make it worse.

I'll try this in a toy project later today and see if there's anything else to be said!

edit 8/5 EOD: Bytedeco doesn't seem to have the same dependency conflicts as other libraries did, which is great! There are still issues at runtime, and transitive dependencies (mkl -> javacpp) don't seem to be automatically included as expected. Will look more into this.