Hello everyone, I'm attempting to create a simple ...

# coroutines

[muliyul]

Hello everyone,
I'm attempting to create a simple implementation for a server-side event bus:

@Singleton
class EventBus {
	private val events = MutableSharedFlow<Any>()

	suspend fun publish(event: Any) {
		events.emit(event)
	}

	@OptIn(DelicateCoroutinesApi::class)
	fun <T : Any> subscribe(clazz: KClass<T>, onEvent: suspend (T) -> Unit) = GlobalScope.launch {
		events.filterIsInstance(clazz).collect { event ->
			ensureActive()
			onEvent(event)
		}
	}
}

I used GlobalScope.launch because it is supposed to live as long as the server is up.

Do you see any issues with this implementation?

[Zach Klippenstein (he/him) [MOD]]

testing: GlobalScope is great for making code untestable

[Zach Klippenstein (he/him) [MOD]]

who calls subscribe? That thing should be responsible for the lifecycle of the subscription. Even if that happens to be "the lifetime of the process" in production, that assumption should not be hard-coded into something like an event bus

[muliyul]

@Zach Klippenstein (he/him) [MOD] do you have I'd appreciate concrete suggestions

[muliyul]

Caller looks like this:

@Singleton
class CreateOrderUseCase @Inject constructor(
  ...
  private val eventBus: EventBus
) : UseCase {

  init {
   eventBus.subscribe(PaymentReceivedEvent::class, ::onPaymentReceived)
  }

[Zach Klippenstein (he/him) [MOD]]

There's another smell, performing side effects in a constructor. This is gonna be untestable too for similar reasons

[kevin.cianfarini]

I feel like your use cases would be covered much more safety by just passing in a shared flow in place of an event bus

[kevin.cianfarini]

Your custom abstraction has no way to unsubscribe which is undoubtedly going to lead to memory leaks

[gildor]

Main issue with this implementaion is that it's own existence
I think you are trying to implement anti-pattern here

[gildor]

Instead of using specific, not shared, rective flows, you downgrade solution to type-unsafe event bus, which was an anti-pattern 10 years ago at least