Hi Is there any known cases when `GlobalScope launch Dispatc

Question

Hi Is there any known cases when `GlobalScope launch Dispatchers Unconfined ` will actually dispatch I stumbled upon some case when `GlobalScope launch start = CoroutineStart UNDISPATCHED context = Dispatchers Unconfined ` = `GlobalScope launch Dispatchers Unconfined ` but I can t quite figure what s causing it

octylFractal · Answer

if you can create a test case I might have some ideas but I think those two should be equivalent from what I know

Vsevolod Ganin · Answer

I m trying but no luck in reproducing it in simple environment yet unfortunately I will get back if I manage to

Vsevolod Ganin · Answer

Okay I managed to pinpoint it This has something to do with Android `Dispatchers Main immediate` parent context Simple test ``` GlobalScope launch Dispatchers Main immediate GlobalScope launch Dispatchers Unconfined println $coroutineContext before println $coroutineContext after ``` It prints ``` CoroutineId 3 coroutine 3 StandaloneCoroutine Active 229841e Main immediate after CoroutineId 4 coroutine 4 StandaloneCoroutine Active f2294ff Unconfined before ``` And if I use `start = CoroutineStart UNDISPATCHED` it works correctly

octylFractal · Answer

I think the key here is `DispatchedContinuation lt gt executeUnconfined` when you are already in an event loop which I believe Dispatchers Main immediate counts as well it will not immediately execute but re dispatch for later to avoid stack overflows

octylFractal · Answer

`CoroutineStart UNDISPATCHED` is a little more strict and does not use the event loop to avoid stack overflows

Vsevolod Ganin · Answer

Strange Using `Dispatchers Main` yield correct result ``` CoroutineId 29 coroutine 29 StandaloneCoroutine Active c6ed5c2 Unconfined before CoroutineId 25 coroutine 25 StandaloneCoroutine Active 65e4fd3 Main after ```

octylFractal · Answer

correct because the non immediate one does not use the undispatched event loop

Vsevolod Ganin · Answer

But do `Main immediate` and `Unconfined` share the same event loop to avoid stack overflows Is it not a private implementation detail

octylFractal · Answer

yes they share the same event loop I believe it is technically an implementation detail of how coroutines are dispatched when `CoroutineDispatcher isDispatcherNeeded` returns false which means that they share it because it is the same mechanism

Vsevolod Ganin · Answer

I see Thank you for your time and help