How long does an event live in the eventbus?

Question

I would like to @Subscribe a method in a Runnable that is created by a ScheduledFuture, so that I can signal it from another thread whether to run. Because a ScheduledFuture creates the object at some future time, there is no scope for the @Subscribe listener to pick up my event. So, I'm wondering how long an event sits in the bus, waiting to picked up by a listener? Is the actual pub-sub synchronous wrt sending/receiving events or will they sit in a queue for some duration before timing out?

Thanks.

Answer 1

Guava's EventBus does not provide sticky events. Additionally, due to the design of EventBus, it's not as straightforward as it could be to extend it to implement such a sticky design, as a lot of the internals are package-private (e.g. the logic to discover which methods on a registered object are annotated with Subscribe and mapping them to the proper event type).

I do think there are some other libraries out there which do provide this, like GreenRobot's event bus (https://github.com/greenrobot/EventBus), but without introducing a new library you'll have to build it more or less from scratch.

An alternative that I've used is RxJava's Observables with a replay(1) operator, so that subscribing to the observable will always immediately invoke the subscription callback with the last item, but it's not a drop-in replacement.