Hi all, does coroutines (or continuations) have so...

# coroutines

[bobby]

Hi all, does coroutines (or continuations) have some kind of "hooks" that we can attach to on resume? Basically I want to intercept the resumption of continuations to do some custom behavior before actually resuming. I hope this question makes sense to you.

[simon.vergauwen]

You can run a coroutine with fun (suspend () -> A).startCoroutine(cont: Continuation<A>)

[simon.vergauwen]

You can wrap this with the suspendCoroutine builder to achieve your use case if I'm not mistaken.

[simon.vergauwen]

May I ask what your use case is? I wanted to build in some error handling for Deferred but was unsuccessful but with regular suspend functions this should work.

[bobby]

Hi, thanks. My use case is I want to instrument coroutines with APM. I want to link the separate threads as a single transaction, so I need to call something like token.link() on each resume

[simon.vergauwen]

Okay, so excessive wrapping might not be desired then.

[bobby]

Yes indeed, ideally I don't have to modify many of the call sites... I'm thinking of overriding/extending ContinuationInterceptor somehow

[bobby]

Btw, could you explain about the startCoroutine + suspendCoroutine? How would it look like?

[voddan]

@bobby yes they do! AFAIK the "hooks" are called interceptors and are a central part of coroutine context. Basically, dispatchers and other parts in coroutine context are (were last time I looking into the code) implemented as interceptors. See https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.coroutines/-continuation-interceptor/index.html

[bobby]

@voddan thanks! yeah I've also read about ContinuationInterceptor and how dispatchers implement that interface. Sadly interceptContinuation seems to be final in CoroutineDispatcher base class so I don't see ways to use it while still using existing dispatchers (default, IO, etc.)

[voddan]

I don't think you need to extend coroutine dispatchers. Rather, you could try making something LIKE a coroutine dispatcher using the same mechanics to intersect suspend points