Consider the following scenario: - High-latency HT...

# coroutines

[Felix]

Consider the following scenario:
- High-latency HTTP requests, done using the Apache Async Client
- Coroutine that "launches" multiple requests using async, obtaining Deferred objects
- Coroutine then cancels one of those Deferred objects.
1) How can such a cancel trigger a cancellation on the pending HTTP request? The Apache Async Client has a way to cancel requests, however since there isn't any thread actively monitoring the isActive, I need to "link" the Deferred cancel with the pending request cancel. For instance, in .NET the CancellationToken as a Register method to register an action to be performed.
2) Also, if the coroutine decides to ignore the cancellation (e.g. it is to late to cancel the HTTP request), how can we observe that on the Deferred? What I'm observing is that the await will throw the JobCancellationException even if the cancel is ignored.

[elizarov]

https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.experimental/-job/invoke-on-completion.html

[Felix]

Thanks.

[Felix]

Regarding 2): when cancelling a Deferred, apparently it will transition immediately to a cancelled state, even if the cancellation is ignored by the underlying coroutine, right?

[Felix]

Or is there a way to make the Deferred state depend on the coroutine reaction to the cancellation request?

[elizarov]

It will become Cancelling. It will become Cancelled only when the underlying coroutine completes. More in that here: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.experimental/-job/index.html