Hey guys, hi! I wonder, how do you handle infinite flow subscriptions? Currently, the only way works...

# orbit-mvi

[Oleksii Malovanyi]

Hey guys, hi!
I wonder, how do you handle infinite flow subscriptions? Currently, the only way works for me is

flow<Unit> {
            while (true) {
                delay(3000)
                emit(Unit)
            }
        }.flowOn(<http://Dispatchers.IO|Dispatchers.IO>).onEach { _ ->
            intent { reduce { it } }
        }.launchIn(viewModelScope)

Unfortunately intent coroutine couldn’t be used for this, as it would block all new messages from the RealContainer’s channel

intent {
            flow<Unit> {
                while (true) {
                    delay(3000)
                    emit(Unit)
                }
            }.flowOn(<http://Dispatchers.IO|Dispatchers.IO>).onEach { _ ->
                intent { reduce { it } }
            }.collect()
        }

[Mikolaj Leszczynski]

I thought we had a test or recommendation for this but for the life of me I can’t find it. I think we need to update our docs.

I think we tested it with something to this extent:

intent {
                withContext(<http://Dispatchers.IO|Dispatchers.IO>) {
                    flow<Unit> {
                        while (true) {
                            delay(3000)
                            emit(Unit)
                        }
                    }.collect {
                        reduce { it }
                    }
                }
            }

[Mikolaj Leszczynski]

let me know whether this works or not - it should in theory but it’s not well tested enough AFAICS

[Mikolaj Leszczynski]

you don’t really need to wrap reduce in intent I don’t think

[Mikolaj Leszczynski]

changing the context should help unblock the orbit event loop (I’m not sure how that relates to flowOn. Mainly you need to make sure that you’re collecting the flow on another dispatcher

[Mikolaj Leszczynski]

If that still doesn’t look like it works, please file a bug report and we’ll look into it

[Mikolaj Leszczynski]

looks like we even have a ticket for it https://github.com/orbit-mvi/orbit-mvi/issues/15

[Oleksii Malovanyi]

@Mikolaj Leszczynski nah, it still won’t work as the parent coroutine from the RealContainer still waits for collect to finish (and it never finishes). I’ve tried to modify RealContainer to receive channel’s messages as a flow in a separate coroutine, but the problem is reduce state is in a race condition then 😞 I’ll try to play around it a bit and propose to move our conversation to github’s issue 🔝

[Mikolaj Leszczynski]

Odd, I need to run some tests too

[Mikolaj Leszczynski]

Just to rule things out, are you observing this behaviour in production code or tests

[Oleksii Malovanyi]

prod

[Oleksii Malovanyi]

I’ll upload test branch with a possible way to fix in 5 mins

[Oleksii Malovanyi]

@Mikolaj Leszczynski https://github.com/orbit-mvi/orbit-mvi/pull/43

[Mikolaj Leszczynski]

Thanks I'll take a look.

[Mikolaj Leszczynski]

Today

[Mikolaj Leszczynski]

This is an important issue 😉

[Oleksii Malovanyi]

btw, as a concept I thought about two more variants:
1. add another dsl method for infinite loops;
2. provide (child) scope as a part of simple context (e.g. for launchIn ) to not to block the intent with collect
But surely wouldn’t go with either if we still could make intent work safely without blocking

[Mikolaj Leszczynski]

Yeah that's what I'm going to try to figure out.

[Mikolaj Leszczynski]

I apologize, we should have tested this better

[Mikolaj Leszczynski]

But I think this feature got lost somewhere when we transitioned from the strict to the simple syntax

[Oleksii Malovanyi]

while your lib is free you should apologise for nothing 😂 still grateful for your efforts

[Mikolaj Leszczynski]

I expect better from myself 😜

[Mikolaj Leszczynski]

Life's been getting in the way of improving this lib though

[Mikolaj Leszczynski]

@Oleksii Malovanyi I’ve figured it out. So the reason it doesn’t work (and why I could have sworn it worked earlier 🤪) is that we broke it when introducing the exception handler change.

Specifically, the supervisorScope will wait until the coroutines inside it are finished. This means it will indeed block forever when we collect an infinite flow. The bug eluded us because it worked when an exception handler was not installed (which is the case for the majority of tests), so unit tests didn’t pick it up.

I’ve replaced the supervisor scope with a job instead, PR ready here: https://github.com/orbit-mvi/orbit-mvi/pull/44

[Mikolaj Leszczynski]

I’ll release a hotfix as soon as this is in

[Mikolaj Leszczynski]

Just tagged https://github.com/orbit-mvi/orbit-mvi/releases/tag/3.1.1

[Oleksii Malovanyi]

@Mikolaj Leszczynski wow! Also the corresponding code looks now much smoother metal I feel a bit bad for introducing the issue, but I also feel thankful for such a quick fix from your side, Thanks!

[Mikolaj Leszczynski]

Relax, it did go through a code review and we haven't noticed!

[Mikolaj Leszczynski]

Code doesn't break only if you never add any new features 😜

[Mikolaj Leszczynski]

Besides it was only confined to people having an exception handler installed, I think we caught it early enough that most people don't have one

[miqbaldc]

thanks #orbit-mvi team & @Oleksii Malovanyi for the report! ❤️

[Mikolaj Leszczynski]

there was some sort of hiccup in the maven central upload process, but we will finalise the release today for sure