bobgodwinx

libdispatch efficiency tips

The libdispatch is one of the most misused API due to the way it was presented to us when it was introduced and for many years after that, and due to the confusing documentation and API. This page is a compilation of important things to know if you're going to use this library. Many references are available at the end of this document pointing to comments from Apple's very own libdispatch maintainer (Pierre Habouzit).

My take-aways are:

• You should create very few, long-lived, well-defined queues. These queues should be seen as execution contexts in your program (gui, background work, ...) that benefit from executing in parallel. An important thing to note is that if these queues are all active at once, you will get as many threads running. In most apps, you probably do not need to create more than 3 or 4 queues.

• Go serial first, and as you find performance bottle necks, measure why, and if concurrency helps, apply with care, always validating under system pressure. Reuse

bobgodwinx

import UIKit
import Foundation
import CoreImage
import MetalPerformanceShaders
// MARK: - Filter Types

enum FilterType {
    case clarendon
    case gingham
    case juno

bobgodwinx

/// `ViewController`
class ViewController: UIViewController {
    private let bag = DisposeBag()
    private let indicator = PublishRelay<RxMBProgressHUD.State>()
    private let viewModel: ViewModelType

    init(_ viewModel: ViewModelType = ViewModel()) {
        self.viewModel = viewModel
        super.init(nibName: nil, bundle: nil)
        configure()

bobgodwinx

/// `ViewModel`
class ViewModel: ViewModelType {
    let source: Driver<UIImage?>
    let finished: Completable

    init(_ model: ModelType = Model()) {
        self.source = model.datasource
            .map { UIImage.gif(data: $0.data) }
            .asDriver(onErrorJustReturn: nil)

bobgodwinx

protocol ViewModelType {
    var source: Driver<UIImage?> {get}
    var finished: Completable {get}
}

bobgodwinx

/// `Model`
struct Model: ModelType {

    let datasource: Observable<Resource>

    init() {
        let url = URL(string: "https://media.giphy.com/media/5z08WdHr0h9SHZekve/giphy.gif")!
        let request = URLRequest(url: url)
        self.datasource = URLSession.shared.rx
            .response(request: request)

bobgodwinx

typealias Resource = (response: HTTPURLResponse, data: Data)

protocol ModelType {
    var datasource: Observable<Resource> {get}
}

bobgodwinx

class RxMBProgressHUD: ObserverType {

    static let shared = RxMBProgressHUD()

    enum State {
        case hide(view: UIView?, animated: Bool)
        case show(view: UIView?, animated: Bool)
    }

    typealias E = RxMBProgressHUD.State

bobgodwinx

github "ReactiveX/RxSwift" ~> 4.2.0

bobgodwinx

target 'LegacyApp' do
  use_frameworks!
  pod 'RxSwift', '~> 4.2.0'
  pod 'RxCocoa', '~> 4.2.0'
end