Peter Steinberger steipete

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

	//
	// UIKit+DynamicStyle.swift
	//
	// Created by kaizei on 2019/7/19.
	// Copyright © 2019 yimi.kaizei. All rights reserved.
	//

	import UIKit

	// MARK: - reflect system style


	struct ViewControllerHolder {
	weak var value: UIViewController?
	init(_ value: UIViewController?) {
	self.value = value
	}
	}

	struct ViewControllerKey: EnvironmentKey {
	static var defaultValue: ViewControllerHolder { return ViewControllerHolder(UIApplication.shared.windows.first?.rootViewController ) }

	import UIKit

	class ViewController: UIViewController {

	override func viewDidLoad() {
	super.viewDidLoad()

	// static images
	let lightImage = UIImage(named: "LightImage")!
	let darkImage = UIImage(named: "DarkImage")!

	//
	// AppDelegate.swift
	// SwiftUITestApp
	//
	// Created by Matt Gallagher on 4/6/24.
	// Copyright © 2019 Matt Gallagher. All rights reserved.
	//

	import Cocoa
	import SwiftUI

	/// Withable is a simple protocol to make constructing
	/// and modifying objects with multiple properties
	/// more pleasant (functional, chainable, point-free)
	public protocol Withable {
	init()
	}

	public extension Withable {
	/// Construct a new instance, setting an arbitrary subset of properties
	init(with config: (inout Self) -> Void) {

	// Douglas Hill, December 2018
	// Made for https://douglashill.co/reading-app/
	// Find the latest version of this file at https://github.com/douglashill/KeyboardKit

	import UIKit

	/// A table view that allows navigation and selection using a hardware keyboard.
	/// Only supports a single section.
	class KeyboardTableView: UITableView {
	// These properties may be set or overridden to provide discoverability titles for key commands.

	//
	// SKSerialInputStream.h
	// inputstream
	//
	// Created by Soroush Khanlou on 11/4/18.
	// Copyright © 2018 Soroush Khanlou. All rights reserved.
	//

	#import <Foundation/Foundation.h>

	// # Why +0 is a better default than +1 for "normal function arguments".
	//
	// My intention here is to show why +0 is better default in a resilient
	// word. Keep in mind that inside individual modules and with inlinable
	// declarations, the optimizer can change conventions at will so from a defaults
	// perspective, these are not interesting. The interesting case is calling
	// non-inlinable functions in other modules.
	//
	// Consider a situation where I have a class Klass and a function foo that calls
	// a function bar in a different module.

	on setDarkMode(shouldBeDark)

	set paneID to "com.apple.preference.general"

	tell application "System Events"
	if dark mode of appearance preferences is shouldBeDark then return
	end tell

	set paneWasOpen to false