I wonder if the following is a UniFlow bug

Question

I wonder if the following is a UniFlow bug UniFlow s internals use `CoroutineScope launch action ` not literally but that s what it comes down to If you create a lot of `action ` actions quickly or if your system is slow then these launched coroutines aren t necessarily run in order Remember launching is fire and forget You don t know when the coroutine is actually run So is my code just an example of bad practice Or is my code an example of a UniFlow running actions in an unordered fashion and is that a bug

Erik · Answer

An alternative approach 1 Start a slow action e g add some delay before setting state 2 Start a fast action immediately after the slow action You will likely see that the effect of the fast action happens before the slow action completes

Erik · Answer

Scratch that last comment the `actor` in the uniflow internals should ensure processing of actions in the order they are sent to it no matter how fast or slow the actions run However my original bug still stands UniFlow uses `launch` to ultimately send actions to the actor which may cause actions going out of order

Erik · Answer

And that seems like a bug bug to me in a state machine with action inputs and state event outputs

arnaud.giuliani · Answer

Hey < Erik> what version do you use

arnaud.giuliani · Answer

gt UniFlow uses `launch` to ultimately send actions to the actor which may cause actions going out of order Ok interesting thinking face

Erik · Answer

For the version see the linked gist 0 11 6

Erik · Answer

Coroutines 1 3 5 but that shouldn t matter

Erik · Answer

Kotlin 1 4 31

Erik · Answer

In other words is it a bug if UniFlow doesn t preserve action order Because then I can file a bug report

arnaud.giuliani · Answer

Did you tried woth last 0 13 0 alpha

arnaud.giuliani · Answer

I agree it should preserve order as much as possible

arnaud.giuliani · Answer

apart if you launch new job without joining them from actions

arnaud.giuliani · Answer

< Erik> here below the new code of the reducer

arnaud.giuliani · Answer

there is no `launch` but just a `withContext` to execute directly the function

Erik · Answer

I think this `launch` is the cause <https github com uniflow kt uniflow kt blob 08b6c921a058605de27463a66f17c1b6b6ef7539 uniflow core src main kotlin io uniflow core flow ActionDispatcher kt L31> It should be a `withContext` or no context switch at all

arnaud.giuliani · Answer

withContext can only be called from a coroutines

arnaud.giuliani · Answer

here we are just enqueing action into the Actor

arnaud.giuliani · Answer

I can write this

arnaud.giuliani · Answer

with a `launchOnMain`

Erik · Answer

I understand it s all because you use `actor send` which is a `suspend fun`

Erik · Answer

So then I would argue that that shouldn t be used but `offer` should be used instead The buffer is there for a reason we should limit concurrency in some way because it s not free When the action buffer is full we can either suspend ignore the action or worse throw

Erik · Answer

Suspending requires launching a coroutine Launching many coroutines doesn t provide order guarantees unless you can maybe launch them in some scope context that preserves launch order

Erik · Answer

So either do not launch and `offer` or use a different scope context `runBlocking` would work but that could block the user so not an option

arnaud.giuliani · Answer

interesting catch +1

arnaud.giuliani · Answer

`offer` could block then but we avoid the coroutines lunch just for offering

Erik · Answer

I would maybe just log an exception when the buffer is full

Erik · Answer

But not block It would lose actions though Not sure what s better Maybe this behaviour can be configurable Just like the shared flow on buffer overflow behaviour

arnaud.giuliani · Answer

Or just log an error thinking face

arnaud.giuliani · Answer

as if we throw an exception we can t do anything either

arnaud.giuliani · Answer

Can go with something simple like that

Erik · Answer

Sure

Erik · Answer

So in conclusion is this being picked up or do I need to do anything e g create an issue

arnaud.giuliani · Answer

already on master muscle

arnaud.giuliani · Answer

I m polishing some last stuff to make the 1 0 0