Hello all wave Is there a channel that emits its value to al

Question

Hello all wave Is there a channel that emits its value to all subscribers while suspending keeping the value if none is subscribed and then the value gets consumed

pablisco · Answer

That sounds a lot like what StateFlow does <https kotlin github io kotlinx coroutines kotlinx coroutines core kotlinx coroutines flow state flow > It emits the latest value to new subscribers AFAIK

George Theocharis · Answer

Yes i ve been using state flow for a different case But state flow won t consume the value after all subscribers received it Well you can do it manually but was wondering if it could be done with another combination out of the box package

pablisco · Answer

It s hard to do I think as the flow channel doesn t know if there are gonna be new subscribers subscribing after Unless I m not fully understanding the use case Which is likely sweat smile

wasyl · Answer

What do you mean consume the value Should new subscribers not receive the value assuming they subscribed after previous consumers received it

George Theocharis · Answer

Yes exactly that I want to model one shot events namely side effects that can propagate to every subscriber until someone handles it Of course i can use state flow and then update the value when it s handled but was wondering as i said if it s something that can help me avoid manually updating after handling

wasyl · Answer

Not sure I follow If you want the value to be handled by all subscribers a regular Flow not `StateFlow` would do just that Unless you want the value to only be handled by a single subscriber

gildor · Answer

Not sure that there is a ready to use primitive for this Essentialy suspend until there are no subscribers and with subscribers work as standard BroadcastChannel SharedFlow

George Theocharis · Answer

What Andrey is saying Yes probably it doesn t exist The closer i have found is the broadcast channel but it doesn t suspend and the other choice is a state flow that also won t suspend but it will have its value saved On that case i will have to manually null out the value after consuming Probably i will go with the state flow Thanks though pray blush

gildor · Answer

Broadcast channel doesn t suspend it will be replaced with SharedFlow which also doesn t suspend in such cases

gildor · Answer

Anyway I would report your case to Kotlinx coroutines tracker some custom operator can be implemented on top of StateFlow you can have an operator which creates StateFlow increments some atomic counter on subscribe and decrement on unsubscribe and buffer value if there is 0 subscribers and emit it on first subscriber

gildor · Answer

originally I thought that you need something like ReplaySubject for flows but it also not what you need if you don t want to emit last N values to new subscribers