there doesn't seem to be a cancelation hook when building a

Deferred

(via

CompletableDeferred

). Is there something else that offers this callback?

invokeOnCompletion

is there. Or what else are you looking for?

I'm wrapping Retrofit's Call. It completes with a result or completes exceptionally. I want to propagate cancellation of the Deferred up into the Call though.

Use

invokeOnCompletion

and cancel call from there. It should work assuming that cancelling an otherwise completed call has no effect.

It's meant to be cheap.

You can also extend

JobSupport

just like

CompletableDeferred

. In this case,

onCancellation

can be overriden. Less stable API, but less overhead.

Can you clarify what you mean by less stable? I thought binary compatibility was guaranteed despite the experimental status.