Also when exactly are coroutines checked for cancelation Wil

Question

Also when exactly are coroutines checked for cancelation Will a suspending function call check for cancelation before the function implementation is invoked Will `withContext` check for cancelation upon before and or after invoking `block` Will `yield` check for cancelation immediately or on after dispatch

bezrukov · Answer

gt Will a suspending function call check for cancelation before the function implementation is invoked it s heavily depends on suspend fun implementation by default suspend fun is not cancellable out of the box so it needs to be designed to support cooperative cancellation e g use built in primitives or check for coroutine state gt Will `withContext` check for cancelation upon before and or after invoking `block` Should be both in general gt Will `yield` check for cancelation immediately or on after dispatch `yield` will check it immediately but will also resumed with exception if job was cancelled before re dispatching Also consider `ensureActive` for checking for cancellation in your non cancellable code

Marc Knaup · Answer

Thank you for the clarification I didn t know about `ensureActive` That seems helpful given that `suspend fun` don t check for cancelation by default unless it calls others that do Do you happen to know a good open source example library app that properly manages various scopes amp contexts and thus can serve as guidance

louiscad · Answer

`withContext` since I don t recall which kotlinx coroutines version does check for cancellation before and after invoking block using its given context which in case of `NonCancellable` will be prevented

uli · Answer

I d expect all suspension points to check for cancelation at least on resume There are not so many ways to cause suspension `Suspend Cancelable Coroutine` `yield` `withContext` `await` and funs calling one of the above what did i forget

octylFractal · Answer

all suspension points can t check cancelation because suspend Continuations is a language feature but coroutines are a library implemented on top of that e g sequences are suspend but they do not cooperate with coroutines and do not dispatch or handle cancelation additionally calling a suspend function will not result in a cancelation check

octylFractal · Answer

another example is until recently Flow basic mechanisms did not check for cancelation

louiscad · Answer

< octylFractal> coroutines are not a library kotlinx coroutines is and as of Kotlin 1 3 it brings cancellation support with `Job` FYI the x in kotlinx stands for extension

octylFractal · Answer

alright I suppose that s true but it doesn t change what I said cancellation is not a concept in the stdlib so not all suspension points check for it

octylFractal · Answer

kotlinx coroutines is what brings cancellation to the table

louiscad · Answer

That s true

Marc Knaup · Answer

Interesting and makes sense Thanks < octylFractal> and < louiscad>