src/main/java/io/reactivex/parallel/ParallelFlowable.java
@CheckReturnValue
    @NonNull
    public final Flowable<List<T>> toSortedList(@NonNull Comparator<? super T> comparator) {
        return toSortedList(comparator, 16);
    }
@CheckReturnValue
    @NonNull
    public final Flowable<List<T>> toSortedList(@NonNull Comparator<? super T> comparator) {
        return toSortedList(comparator, 16);
    }
Sorts the 'rails' according to the comparator and returns a full sorted list as a Publisher.
<p>
This operator requires a finite source ParallelFlowable.

@param comparator the comparator to compare elements
@return the new Flowable instance