Tim Oliver TimOliver

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

	import UIKit

	#if canImport(SwiftUI) && DEBUG
	import SwiftUI
	struct UIViewControllerPreview<ViewController: UIViewController>: UIViewControllerRepresentable {
	let viewController: ViewController

	init(_ builder: @escaping () -> ViewController) {
	viewController = builder()
	}

	#!/bin/zsh

	# pkgAndNotarize.sh

	# 2019 - Armin Briegel - Scripting OS X

	# place a copy of this script in in the project folder
	# when run it will build for installation,
	# create a pkg from the product,
	# upload the pkg for notarization and monitor the notarization status

	import UIKit

	extension UIBezierPath {

	/**
	Draws the super-elliptic analog of a rounded rect. Unlike the regular rounded rect, the rounded corners
	are the quadrants of a superellipse (i.e., parabolic segments), _not_ circular arcs.
	If `rect` is a square and `cornerRadius` is equal to half the length or more, and actual superellipse is
	drawn (no straight sections along its boundary) just like doing the same with a rounded rect results in a
	circle being drawn.

	/// An extension to provide conversion to and from CIELCh° colors.
	extension UIColor {

	/// The CIELCh° components of a color - lightness (L), chroma (C), and hue (h).
	struct CIELCh: Hashable {

	/// The lightness component of the color, in the range [0, 100] (darkest to brightest).
	var L: CGFloat
	/// The chroma component of the color.
	var C: CGFloat

	@import Foundation;

	NS_ASSUME_NONNULL_BEGIN

	FOUNDATION_EXTERN NSString * const RingerSwitchDidChangedNotification;

	@interface RingerSwitchObserver : NSObject

	@property (nonatomic, readonly, getter=isSlient) BOOL silent;

	//
	// Switch.swift
	// Re-Engineering UISwitch
	//
	// Created by Nathan Tannar on 15/12/18.
	// Copyright © 2018 Nathan Tannar. All rights reserved.
	//

	import UIKit

	https://statici.icloud.com/fmipmobile/deviceImages-9.0/iPhone/iPhone9,4-2-3-0/online-infobox__3x.png
	A B C D E F G

	A: deviceImages version seems to determine the format of the image specifier (C, D, E, F)
	B: device marketing name
	C: device model identifier
	D: front color (DeviceColor)
	E: back color (DeviceEnclosureColor) (missing on very old devices)
	F: color (device cover/backing/housing)?? (missing on older devices)
	G: image variant

	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