Allen Wu allewun

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

DEPRECATED for Xcode 10 🎈

(check out What's New in Swift at 11:40, slide 42)

Whole Module Compilation Optimizations: Why these terms are sometimes misleading

When you look up how to compile swift faster for debug builds, people very earnestly give advice that seems contradictory: you should "try using the whole module optimization flag," and also "never use whole module optimization for debugging". [^1]

This is confusing because some of us are using these two general words:

compilation: "turning text into an executable program"

Following the tradition from last year, here's my complete list of all interesting features and updates I could find in Apple's OSes, SDKs and developer tools that were announced at this year's WWDC. This is based on the keynotes, the "What's New In ..." presentations and some others, Apple's release notes, and blog posts and tweets that I came across in the last few weeks.

If for some reason you haven't watched the talks yet, I really recommend watching at least the "State of the Union" and the "What's New In" intros for the platforms you're interested in. The unofficial WWDC Mac app is great way to download the videos and keep track of what you've already watched.

If you're interested, here are my WWDC 2015 notes (might be useful if you're planning to drop support for iOS 8 now and start using some iOS 9 APIs).

	#!/bin/bash

	# Script for cleaning MacOS related trash (dot files and folders)
	# from a removable disk and unmounting that disk.
	# Script does sanity checks, should be safe, but use at your own risk!

	# Newest version can always be found at https://gist.github.com/pawelszydlo/5eacd49d7e57bce71e96171e9fad1cd2


	# Display a dialog box.

	// For the best results, your tableHeaderView/tableFooterView should be a UITableViewHeaderFooterView with your content inside the contentView.
	let tableHeaderView = UITableViewHeaderFooterView()

	let fittingSize = CGSize(width: tableView.bounds.width - (tableView.safeAreaInsets.left + tableView.safeAreaInsets.right), height: 0)
	let size = tableHeaderView.systemLayoutSizeFitting(fittingSize, withHorizontalFittingPriority: .required, verticalFittingPriority: .fittingSizeLevel)
	tableHeaderView.frame = CGRect(origin: .zero, size: size)
	tableView.tableHeaderView = tableHeaderView

	// When you set this view to the tableHeaderView/tableFooterView on the table view, the table view will preserve the existing size of its frame.
	// If you need to change the size, remove the tableHeaderView/tableFooterView, set a new frame on it, then re-set it on the table view again.

	<?xml version="1.0" encoding="UTF-8"?>
	<Bucket
	type = "4"
	version = "2.0">
	<Breakpoints>
	<BreakpointProxy
	BreakpointExtensionID = "Xcode.Breakpoint.SymbolicBreakpoint">
	<BreakpointContent
	shouldBeEnabled = "Yes"
	ignoreCount = "0"

Allen Wu allewun

libdispatch efficiency tips

DEPRECATED for Xcode 10 🎈

(check out What's New in Swift at 11:40, slide 42)

Whole Module Compilation Optimizations: Why these terms are sometimes misleading

OSX → macOS 10.12 Sierra