Combine a list of Observables and wait until all completed

Question

TL;DR How to convert Task.whenAll(List) into RxJava?

My existing code uses Bolts to build up a list of asynchr

Answer 1

I'm writing some computation heave code in Kotlin with JavaRx Observables and RxKotlin. I want to observe a list of observables to be completed and in the meantime giving me an update with the progress and latest result. At the end it returns the best calculation result. An extra requirement was to run Observables in parallel for using all my cpu cores. I ended up with this solution:

@Volatile var results: MutableList = mutableListOf()

fun doALotOfCalculations(listOfCalculations: List): Observable> {

    return Observable.create { subscriber ->
        Observable.concatEager(listOfCalculations.map { calculation: Calculation ->
            doCalculation(calculation).subscribeOn(Schedulers.computation()) // function doCalculation returns an Observable with only one result
        }).subscribeBy(
            onNext = {
                results.add(it)
                subscriber.onNext(Pair("A calculation is ready", it))

            },
            onComplete = {
                subscriber.onNext(Pair("Finished: ${results.size}", findBestCalculation(results)) 
                subscriber.onComplete()
            },
            onError = {
                subscriber.onError(it)
            }
        )
    }
}