How can I cancel a coroutine I started with `start...

# coroutines

[simon.vergauwen]

How can I cancel a coroutine I started with startCoroutineCancellable?

[altavir]

why do you use startCoroutineCancellable?

[simon.vergauwen]

To run a suspend function with a callback instead of a suspension.

[simon.vergauwen]

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]

You probably should see how it done in kotlinx.coroutines

[simon.vergauwen]

Where?

[altavir]

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

[simon.vergauwen]

I meant see how what is done?

[altavir]

Cancelation for builders.

[simon.vergauwen]

AFAIK they do so with Scope and Job

[simon.vergauwen]

but all of that is not available from startCancellableContinuation

[Vsevolod Tolstopyatov [JB]]

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]

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]]

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

[Vsevolod Tolstopyatov [JB]]

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

[simon.vergauwen]

I want to start a given suspend () -> A on a given CoroutineContext within a Continuation.

[simon.vergauwen]

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)
      }
}

[simon.vergauwen]

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

is the piece of code I am still missing

[simon.vergauwen]

Fiber is an alias for two actions Pair(join, cancel)

[simon.vergauwen]

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