Can anybody explain me why do sequenced setting value in MutableStateFlow doesn’t emit until last va...

# coroutines

[iamthevoid]

Can anybody explain me why do sequenced setting value in MutableStateFlow doesn’t emit until last value set?

there is simplified example of what i do in my app in thread.

i try to collect combined value from state flow, and emits are sequenced (lines 25, 26)

[iamthevoid]

Sorry , i didn’t embed line numbers in screenshot

25.        state.value = "next"
26.        state.value = Date()

[iamthevoid]

when i do like i show at screenshot i get next output

each: Sun Jan 09 12:16:15 MSK 2022
each: Sun Jan 09 12:16:15 MSK 2022
Thu Jan 01 03:00:00 MSK 1970: start
Sun Jan 09 12:16:15 MSK 2022: start

I got default values (start and date0) and then last emitted date

[iamthevoid]

when i flip lines 25 and 26 i got

each: next
each: next
Thu Jan 01 03:00:00 MSK 1970: start
Thu Jan 01 03:00:00 MSK 1970: next

opposite situation, date not emitted, but string does

[iamthevoid]

looks like backpressure problem, but how can i pass backpressure strategy into state flow?

[iamthevoid]

onEach call shows that first value just not emitted

[iamthevoid]

i tried many ways = state.value = , state.updateAndGet , state.emit , state.tryEmit but result alwas the same

[Joffrey]

State flow values are conflated. State flows are supposed to represent a state for which you only care about the latest value. You would be relying on a race if you relied on getting all change events

[Joffrey]

Also note that here you're in a multithreaded environnement, so you might have a chance by relying on a race. If you weren't, you would be guaranteed to miss the first value assignment, because setting the value of the flow is not a suspending operation, so other coroutines don't have a chance to run between the 2 assignments

[iamthevoid]

Is there any way in coroutines api to do what am i want? Use single source of sequenced values, and filter it by any rule (without worry about values misssing)

[iamthevoid]

Looks like StateFlow doesn’t RxJava subject equivalent at all

[Joffrey]

Maybe look into SharedFlow instead. They are for representing more general hot flows like this. State flow is a special case of it, optimized for conflated state.

[iamthevoid]

Thanks, looks like i did the thing