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kotlinlang

What's the best way to emit items from an observable iff another observable hasn't emitted in a certain amount of time, in which case the first observable should emit, followed by the second observable?

The use case is I have a list cached that I want to emit iff a network call to get an updated list hasn't come back yet, so I want to either only emit the updated list, or emit the cached list followed by the updated list.

So far I've been able to use `amb` to achieve the first part, but I can't figure out how to emit from both observables if the network one doesn't finish fast enough:

```
val cachedObservable = Observable.from(...).delay(500, TimeUnit.MILLISECONDS)

val networkObservable = observable {
  val newList = getUpdatedListFromNetwork()
  if(!it.isUnsubscribed) it.onNext(newList)
}

return Observable.amb(cachedObservable, networkObservable)
```