And yet another question Inside a `produce` does `this close

Question

And yet another question Inside a `produce` does `this close `cancel the producer Is this documented

Vsevolod Tolstopyatov [JB] · Answer

No it s not It s not directly documented though it s principle of least surprise and all cancellations close relations are documented

uli · Answer

I thought I understand coroutines but now I doubt slightly smiling face Did you see my gist trying to show an implementation of switchMap to < hannesstruss> There are 2 funny things 1 If I use coroutines 0 23 1 with the new global coroutineScope it breaks 2 It magically terminates on `output close ` which is a good thing but unexpected

uli · Answer

I guess 2 is solved Calling output close will let switchMapped toList finish in the main coroutine which will close the receive channel which is documented to cancel the producer So I better add a termination point to the producer to not depend on this external closing

Vsevolod Tolstopyatov [JB] · Answer

Old coroutine context is deprecated for a reason slightly smiling face Your code has a bug ``` source switchMap coroutineContext i gt produce coroutineContext lt wrong context here is inherited because switchMap lambda doesn t implement CoroutineScope ```

Vsevolod Tolstopyatov [JB] · Answer

E g ``` val switchMapped = source switchMap coroutineContext i gt println Parent Job for producer $ kotlin coroutines experimental coroutineContext Job vs $ coroutineContext Job ``` will print ` StandaloneCoroutine Active 3941a79c vs BlockingCoroutine Active 27bc2616` respectively Your implementation has a bug accidentally making parent child relationship for all jobs slightly smiling face < hannesstruss> implementation looks good modulo cancellation

uli · Answer

Thanks < Vsevolod Tolstopyatov JB > for pointing this out I still don t get it though What s wrong with the parent child relation I thought this was good practice as it let s you cancel the whole tree I guess we do agree that the transformer jobs are always leafs in the tree Shouldn t it be side effect free to cancel them And should Done be never printed if the transformer job is canceled

uli · Answer

And by the way using coroutines 0 22 3 the code still works even with the global coroutineContext

uli · Answer

Well I see the transformer job is not a leaf node As you pointed out the map producer is created as a child of the transformer job So I guess what happens is that the map producer as a child is canceled before the transformer job parent Now I start guessing Does canceling the producer get the consumeEach out of suspend which will cause the cancelation for the transformer job to be postponed until next suspension

uli · Answer

Yes looks like it If I put a `yield`behind the consumeEach to give another cancelation point things start working again With 0 22 3 the yield was not required which seems more natural to me

uli · Answer

< hannesstruss> ^^^