Hi, I'm trying to transform a callback-based function to a coroutine. Here's what I have so far ```...

# coroutines

[Pacane]

Hi, I'm trying to transform a callback-based function to a coroutine. Here's what I have so far

suspend fun fastSubscribe(path: String): Value =
            suspendCancellableCoroutine { cont: CancellableContinuation<Value> ->
                val handler = object : Handler<SubscriptionValue> {
                    override fun handle(event: SubscriptionValue) {
                        requester.unsubscribe(path, this)
                        cont.resume(event.value)
                    }
                }

                requester.subscribe(path, handler)
            }

Here I want to finish the execution with the value in the callback when I have one, but I'd like to add a timeout for if I never get a value (ie: when handle is never called)

I think I should use a withTimeout in there but I don't know where exactly. On timeout I need to call requester.unsubscribe(handler) , so having the withTimeout on the call site of fastSubscribe isn't really a solution. Is there anything I can do with this?

[tseisel]

Since withTimeout will try to cancel the running coroutine after the time limit has been reached, you could register a listener with cont.invokeOnCancellation to dispose the subscription if its result has not been received.

[streetsofboston]

The 'withTimeout' would go above/around the suspendCancellableCoroutine, but there you won't have access to the 'handler' to unregister it.... Tricky.

Not sure, but you could try to use a call to 'async' instead and wrap the 'withTimeout' around the call to 'await()' of the 'async'....

[streetsofboston]

Ah.... @tseisel answer is great. You can examine in the invokeOnCancellation how continuation ended or how it was cancelled.

[Pacane]

Yes that's what I'm trying to do right now, seems to be a good path

[Pacane]

Works perfectly! thanks @tseisel