4 ms·

Do you have experience doing async ffi to other runtimes from Rust? Such as passing down futures from Rust to JavaScript or Java so you can use them from their

• mmastrac 7y ago
  I can definitely talk about how we did it - maybe see if we can get something up on our blog. Our current approach-du-jure uses callback handles in combination with channels to let the ffi code trigger a real rust future's completion. This has worked reasonably well, but I'm sure we'll experiment with a few other patterns. We don't specifically interface with Java Futures (no particular reason other than it hasn't seemed necessary to add that complexity), but that would be a pretty cool library to build on top of the existing Rust jni crate. One thing I'd like to pass by the Rust community is our internal "teleporter" that allows you to borrow an object mutably on one thread and then "teleport" an immutable ref to that object to any other thread using only a u64 handle (with obviously huge unsafe flags). This has been very handy for some of our async ffi work. I'm hoping to get a few more Rustaceans onboard (aggressively hiring!) over the next few months so we can focus more deeply on some of these interesting problems.
  • pjmlp 7y ago
    If your Java usage is constrained to Android there is a JNI workaround that many NDK folks tend to use. Instead of doing JNI calls, send Android messages between NDK and Framework threads. There is the setup of MessageHandler on both sides, but long term they are more productive than JNI boilerplate.
    • mmastrac 7y ago
      Interesting - do you mean using the Android handler/message infrastructure? I hadn't considered that at all. Do you have any references?
      • pjmlp 7y ago
        Yes. One example would be SDL, although they use a mix of JNI and messages (search for SDLCommandHandler). http://hg.libsdl.org/SDL/file/abb47c384db3/android-project/app/src/main/java/org/libsdl/app/SDLActivity.java http://hg.libsdl.org/SDL/file/abb47c384db3/android-project/a... http://hg.libsdl.org/SDL/file/abb47c384db3/src/core/android/SDL_android.c http://hg.libsdl.org/SDL/file/abb47c384db3/src/core/android/... EDIT: Sorry forgot about the C side (counterpart is Android_JNI_SendMessage).
  • samcday 7y ago
    > One thing I'd like to pass by the Rust community is our internal "teleporter" that allows you to borrow an object mutably on one thread and then "teleport" an immutable ref to that object to any other thread using only a u64 handle (with obviously huge unsafe flags). This has been very handy for some of our async ffi work. Would love to see a blog post (or better yet, library!) for this - sounds interesting!