Hey all can you guys explain me a little bit about EmptyCoroutineContext and ContinuationInterceptor...

# coroutines

[Joan Colmenero]

Hey all can you guys explain me a little bit about EmptyCoroutineContext and ContinuationInterceptor I do not get it at all. I'm learning about coroutine contexts and I found these

[Zach Klippenstein (he/him) [MOD]]

EmptyCoroutineContext is a CoroutineContext that doesn’t have any elements. It’s an “identity” value for addition (EmptyCoroutineContext + someOtherContext == someOtherContext).

It’s useful as a default value for context parameters.

[Zach Klippenstein (he/him) [MOD]]

ContinuationInterceptor is something that can wrap every Continuation generated by the language within a particular CoroutineContext. It is how CoroutineDispatcher is implemented: whenever a Continuation is generated, CoroutineDispatcher wraps that continuation one that will “post” the original continuation on the correct thread pool.

It’s a pretty low-level tool, probably not something you ever need to implement directly.

[zak.taccardi]

What are reasons to use EmptyCoroutineContext over Dispatchers.Unconfined?

[Zach Klippenstein (he/him) [MOD]]

They’re completely different. If the context is EmptyCoroutineContext, that means no dispatcher is specified, so when launching a new coroutine, the runtime will pick the default dispatcher (Dispatchers.Default).

If the context contains Dispatchers.Unconfined, then it’s the same as specifying any other dispatcher in the context – new coroutines will use that dispatcher.

When adding to another context, EmptyCoroutineContext has no effect whereas Dispatchers.Unconfined will override the dispatcher:

(myContext + EmptyCoroutineContext)[ContinuationInterceptor] == myContext[ContinuationInterceptor]

(myContext + Dispatchers.Unconfined)[ContinuationInterceptor] == Dispatchers.Unconfined

[zak.taccardi]

Do you ever use Dispatchers.Unconfined?

[zak.taccardi]

I guess I’m trying to pin down use cases

[zak.taccardi]

for testing, I simply use the CoroutineScope from runBlocking { } or runBlockingTest { }

[zak.taccardi]

and in prod code, all dispatchers are injected

[Zach Klippenstein (he/him) [MOD]]

I’ve used Unconfined for “wiring” coroutines – coroutines that just shuffle data between other communication mechanisms – because it doesn’t make sense to waste time hopping around threads just to make thread-safe calls.

[Joan Colmenero]

Thanks for yout answer @Zach Klippenstein (he/him) [MOD] but what's the purpose to use these?

[Zach Klippenstein (he/him) [MOD]]

`EmptyCoroutineContext`:

It’s useful as a default value for context parameters.

`ContinuationInterceptor`:

It’s a pretty low-level tool, probably not something you ever need to implement directly.