Hey I have a question on `async` and cancellations...

# coroutines

[Pim]

Hey I have a question on async and cancellations. Lets say I have:

withContext(dispatcher) {
    val job = async { while(true) { delay(150) } }
    withTimeoutOrNull(200) { job.await() }
}

Id think this would start some async job, and then wait for its completion for 200ms. If the job takes longer than 200ms, it cancels the await and the async job.
Right now it looks like nothing times out. Am I missing something?

[Dmitry Khalanskiy [JB]]

Only { job.await() } gets cancelled in this case, that is, the process of waiting for the job to complete. Nothing cancels the job itself.
Related issue: https://github.com/Kotlin/kotlinx.coroutines/issues/4329

[Pim]

Thanks for the quick response. Would it be okay to than cancel the job myself on receiving null from the withTimeoutOrNull. Or would there be a better/cleaner way of achieving what I want?

[Dmitry Khalanskiy [JB]]

Or would there be a better/cleaner way of achieving what I want?

This depends entirely on what you want!
How about this?

withContext(dispatcher) {
    val job = async {
        withTimeoutOrNull(200) {
            while(true) { delay(150) }
        }
    }
    job.await()
}

[Pim]

Ahh smart, I did not think of this solution. Thanks a lot, I’ll give it a try!

[uli]

In your example, there is no need for async at all. If this is not only an artefact of creating a minimalist example, you can just drop async completely:

withTimeoutOrNull(200) {
    withContext(dispatcher) {
        while(true) { delay(150) }
    }
}