Best pattern for using RPC in multi-threaded Environment

[rschulman]

I'm trying to use capnproto-rpc in a Tauri app, and Tauri's model is using multi-threaded tokio, so I'm running into the !Send problems. This issue has been discussed in a number of different issues, and some solutions have been suggested, but I haven't seen a really concrete recommendation made anywhere. I'm also not deep enough in the tokio weeds to fully get how to implement it myself.

@dwrensha sketched out an idea in #271, and I'll admit that I had found the idea of inserting a channel in the middle to be kinda hacky and annoying, and likely prone to losing the nicely typed interface that CapnProto would provide. The idea of sending a closure down the channel was interesting, however, but I can't quite get the sketch from #271 fleshed out enough to work. The compiler wants a concrete type for the channel created on the first line of new and I don't know what the intention was for the argument of the closure, or quite what role the closure was supposed to play.

I also don't know if there's been any progress on this issue since 2022 such that there's a better answer to the overall question at this point.

Happy to be educated and figure out what the easiest route is to get the RPC system working with Tauri. Thanks!

[rschulman]

Bumping this once to see if there's any thoughts out there. @dwrensha , any advice? Thanks!

[dwrensha]

I forget what I was thinking in that sketch. It's possible that it doesn't work. It seems that if f is going to do anything interesting with capnp-rpc, then it's going to need to be non-Send, but then it can't get sent across threads in the first place.

[rschulman]

Ahh, ok, that makes sense. So it looks like using a channel to ferry data back and forth is the only option, yeah?