Danny Ruiz ynnadrules

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

	#!/bin/sh

	###
	# SOME COMMANDS WILL NOT WORK ON macOS (Sierra or newer)
	# For Sierra or newer, see https://github.com/mathiasbynens/dotfiles/blob/master/.macos
	###

	# Alot of these configs have been taken from the various places
	# on the web, most from here
	# https://github.com/mathiasbynens/dotfiles/blob/5b3c8418ed42d93af2e647dc9d122f25cc034871/.osx

	#########################
	# .gitignore file for Xcode4 and Xcode5 Source projects
	#
	# Apple bugs, waiting for Apple to fix/respond:
	#
	# 15564624 - what does the xccheckout file in Xcode5 do? Where's the documentation?
	#
	# Version 2.6
	# For latest version, see: http://stackoverflow.com/questions/49478/git-ignore-file-for-xcode-projects
	#

	#/usr/bin/env bash

	set -e
	set -x

	apt-get update
	apt-get upgrade

	apt-get -y install build-essential curl git-core openssl libreadline6 libreadline6-dev \
	zlib1g zlib1g-dev libssl-dev libyaml-dev libsqlite3-0 libsqlite3-dev sqlite3 libxml2-dev \

	CGFloat ScaleToAspectFitRectInRect(CGRect rfit, CGRect rtarget)
	{
	// first try to match width
	CGFloat s = CGRectGetWidth(rtarget) / CGRectGetWidth(rfit);
	// if we scale the height to make the widths equal, does it still fit?
	if (CGRectGetHeight(rfit) * s <= CGRectGetHeight(rtarget)) {
	return s;
	}
	// no, match height instead
	return CGRectGetHeight(rtarget) / CGRectGetHeight(rfit);

	def self.dedupe
	# find all models and group them on keys which should be common
	grouped = all.group_by{\|model\| [model.title,model.info,model.address,model.phone] }
	grouped.values.each do \|duplicates\|
	# the first one we want to keep right?
	first_one = duplicates.shift # or pop for last one
	# if there are any more left, they are duplicates
	# so delete all of them
	duplicates.each{\|double\| double.destroy} # duplicates can now be destroyed
	end

Danny Ruiz ynnadrules

libdispatch efficiency tips

Architecture

Offline Sync and Cache

	import Cocoa


	class WindowController: NSWindowController {
	}

	class AppDelegate: NSObject {
	var mainWindow: NSWindow?
	var mainController: NSWindowController?
	}

	import Foundation
	import UIKit


	/// Used to create a layout guide that pins to the top of the keyboard
	final class KeyboardLayoutGuide {

	private let notificationCenter: NotificationCenter
	private let bottomConstraint: NSLayoutConstraint

	import Combine
	import Foundation

	// MARK: - Polling
	/// A thread safe polling(repeat task over given time) handler object
	public actor Polling {
	public typealias TaskItem = () async -> Void
	public typealias PollingTask = Task<Void, Never>
	typealias PollingSubject = CurrentValueSubject<Int, Never>