Does anybody have a project with a guava event bus...

# coroutines

[groostav]

Does anybody have a project with a guava event bus on it and suspending/async-ing subscribers? I would very much like to have @guava.Subscribe suspend fun handle(event: MyEvent) functions, but by default guava has no idea how to handle that.

I've tried:
1. switching my tests to invoke handlers directly. This works for tests but has trouble with some of our components
2. adding an obnoxious inheritance system to try and keep a List<Job> on the event itself, that gets appended to by subscribers. This is not great.

I'd be willing to take a fork of evenBus just for support for concurrent & synchronous event publication, especially if I can get it without retrofitting existing blocking java code.

[Evan R.]

What’s the purpose of making the handle() function a suspend function? Is it called by other things or are you trying to get it to be handled in some coroutine context?

[Evan R.]

i.e. are you trying to make the handling of an event not block the bus?

[groostav]

a summary of my problem: we post events when things change. Sometimes that kicks off "autosave", a big suspending IO operation. Right now we dot hat operation asynchronously and with bugs. It would be simpler if I could have the autosave operation be a suspend (read: synchronous & concurrent) operation, but to do that, it needs to back-pressure the caller of post by suspend-ing it.

[groostav]

it strikes me that an extension function on EventBus and inheritence on events (sigh) is still the best way to go.

[Evan R.]

Either way you’ll need to end up blocking a thread unless you want to rewrite EventBus to be suspending from the ground up. It’s asynchronous under the hood using java Executor based on what I’ve seen on github

[Evan R.]

If order doesn’t matter you might be able to spin up your own thread pool and convert it to a coroutine dispatcher, then toss autoSave() calls into the pool via launch()

[Evan R.]

If order does matter you’ll need to block the subscriber’s thread via a buffered channel with sendBlocking()

[Evan R.]

Then just toss some coroutine workers into the thread pool