Foreign BackgroundQueue type

[bendk]

A common pattern we use in application-services is to run SQLite queries using a foreign-managed task queue (Dispatchers.IO on Kotlin, DispatchQueue on Swift, etc). Could UniFFI support this as a first-class type?

This would require:

• Moving it across the FFI (only supporting Foreign -> Rust is probably fine)
• Adding way to execute Rust synchronous code using the foreign DispatchQueue in two modes:
  • async mode where you await the result
  • fire-and-forget mode where you just want the code to run and don't care about the result.

[bendk]

I think BackgroundQueue is a nicer name than DispatchQueue, since the feature is really about running tasks in a background thread. I feel like there could be a better name though, open to any suggestions.

[mhammond]

"background thread" implies "low priority thread" to me, which I don't think is the actual intent. The actual use-cases here tend to be more about thread blocking than thread priority. I was going to suggest something like TaskQueue, but depending on the content the Task part of that might itself carry baggage. WorkQueue? But I don't think it matters that much though.

[bendk]

You're right, it really is about blocking more than anything. tokio separates their threads into "worker threads" and "blocking threads". What about BlockingQueue or BlockingTaskQueue?

[mhammond]

using the same terminology as tokio is certainly appealing!