perform task for each element in list in many threads with rxjava2

rxListOfTasks.kt

    // perform task for each element in list in many threads with rxjava2
    fun getAppsList2(): Single<MutableList<UserApp>>? {
        val pm = context.packageManager
        val packages = pm.getInstalledApplications(PackageManager.GET_META_DATA)
        val tasks: MutableList<ApplicationInfo> = mutableListOf()

        packages.mapTo(tasks) { it }

        return Observable.fromIterable(tasks)
                .map { appInfo ->
                    Observable.fromCallable {
                        val name = appInfo.packageName
                        val label = appInfo.loadLabel(pm).toString()
                        UserApp(name, label)
                    }
                }.map { task -> task.subscribeOn(Schedulers.io()) }
                .flatMap { t -> t }
                .toList()
    }