How do you make a long running, blocking function ...

# coroutines

[natario1]

How do you make a long running, blocking function cancellable? E.g. with this third-party class:

class Worker {
  fun doWork()
  fun cancelWork()
}

My attempt below (untested) doesn't look very good, I wonder if there's any better way.

coroutineScope {
  val job = launch {
    while (isActive) {
      delay(50)
    }
  }
  job.invokeOnCompletion { 
    if (it is CancellationException) {
      worker.cancelWork()
    }
  }
  worker.doWork()
  job.cancel()
}

[araqnid]

you can access the current job inside launch{} as coroutineContext[Job] which would probably read better. I think with that there’s no need for the explicit cancel, just sth like:

launch {
  coroutineContext[Job]!!.invokeOnCompletion {
    if (it is CancellationException) {
      worker.cancelWork()
    }
  }
  worker.doWork()
}

I also think that means there’s no need for the outer scope coroutine which is only there to cancel the inner one.

[natario1]

Doesn't seem to work: https://pl.kotl.in/TEgYBGFYo
I think that invokeOnCompletion is not called until doWork() realizes it has been canceled, which won't happen because it's not a coroutine-based API. Unless we spawn a second coroutine

[natario1]

With both attempts here in case you want to play with it https://pl.kotl.in/401iKiPLy second one works