How can I cancel a coroutine I started with `startCoroutineC kotlinlang #coroutines

I trying building an effect system on top of suspend functions. I almost finished it using only what is in kotlin std but I got stuck with cancellation.

altavir

02/04/2019, 1:35 PM

You probably should see how it done in

kotlinx.coroutines

simon.vergauwen

02/04/2019, 1:35 PM

Where?

altavir

02/04/2019, 1:36 PM

https://github.com/Kotlin/kotlinx.coroutines

simon.vergauwen

02/04/2019, 1:36 PM

I meant see how what is done?

altavir

02/04/2019, 1:37 PM

Cancelation for builders.

simon.vergauwen

02/04/2019, 1:38 PM

AFAIK they do so with

Scope

and

Job

but all of that is not available from

startCancellableContinuation

Vsevolod Tolstopyatov [JB]

02/04/2019, 1:56 PM

startCoroutineCancellable

is internal API and is not intended to be used externally. E.g. it is cancellable only when it is used with interceptor from

kotlinx.coroutines

and when used on instance of

DispatchedContinuation

simon.vergauwen

02/04/2019, 1:57 PM

Okay. Is there another way I can achieve this? I frequently use

startCoroutine

to bridge between suspending world and non suspending world but there is no way to take in account cancellation as far as I know.

Vsevolod Tolstopyatov [JB]

02/04/2019, 1:57 PM

Could you please describe your use-case with a sample of code with the desired behaviour? Maybe there are other ways to do what you want

currently, cancellation is available (publicly) on suspension points when used with

suspendCancellableCoroutine

simon.vergauwen

02/04/2019, 2:03 PM

I want to start a given

suspend () -> A

on a given

CoroutineContext

within a

Continuation

Copy code

class Fx<A>(val fa: suspend () -> A) {
  ...

  fun startOn(ctx: CoroutineContext): Fx<Fiber<ForFx, A>> =
      Fx {
        val promise = UnsafePromise<A>()
      
        fa.startCoroutine(asyncContinuation(ctx) { either ->
          either.fold(
            { promise.complete(it.left()) },
            { promise.complete(it.right()) }
          )
        })
      
        val cancel: Fx<Unit> = Fx { Unit /* cancel running coroutine */ }

        FxFiber(promise, cancel)
      }
}

val cancel: Fx<Unit> = Fx { Unit /* cancel running coroutine */ }

is the piece of code I am still missing

Fiber is an alias for two actions

Pair(join, cancel)

@Vsevolod Tolstopyatov [JB] basically build this but with cancellation support https://github.com/Kotlin/kotlin-coroutines-examples/blob/master/examples/run/launch.kt

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