Make two async calls and not returning until both come back or fail

TwoAsyncCalls.java

    override fun removeArtistFromSystem(artistId: Long): Promise<Boolean> {
        return Promises.invokablePromise { promise ->

            val saveSystemDataPromise = Promises.promiseBoolean()
                    .catchError { e -> logger.info("removeArtistFromSystem:: unable to save system data for $artistId", e) }

            val removeArtistFromSystemPromise = Promises.promiseBoolean()
                    .catchError { e -> logger.info("removeArtistFromSystem:: unable to remove $artistId from repo", e) }

            Promises.all(saveSystemDataPromise, removeArtistFromSystemPromise)
                    .then {
                        promise.resolve(true)
                    }
                    .catchError { e ->
                        promise.reject(e)
                    }

            systemData.artistIds.remove(artistId)
            saveSystemData(saveSystemDataPromise)
            artistRepo.removeArtistFromSystem(artistId).invokeWithPromise(removeArtistFromSystemPromise)
        }
    }