completable
fun <R> completableUsing(resourceSupplier: () -> R, resourceCleanup: (resource: R) -> Unit, eager: Boolean = true, sourceSupplier: (resource: R) -> Completable): Completable
Returns a Completable that for each subscription acquires a new resource via resourceSupplier, then calls sourceSupplier and subscribes to the returned upstream Completable and disposes the resource via sourceSupplier when the upstream Completable is finished (either terminated or disposed).
Please refer to the corresponding RxJava document(https://reactivex.io/RxJava/javadoc/io/reactivex/Completable.html#using-java.util.concurrent.Callable-io.reactivex.functions.Function-io.reactivex.functions.Consumer-boolean-.