100mango

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

Generalized existentials 😄 In progress!
- Use case: implement Resource<T>, Siesta’s most obvious API design gap
- Use case: silly dances like this
✅ $0 ≠ all params
Fix anonymous closure argument goofiness (bug, older bug)

Use case: I specifically made the more-frequently used closure arg the second one here so that code referencing only it as $1 would compile (where it would not if it were $0)

Swift Concurrency Manifesto

Author: Chris Lattner

Chinese Translation by Jason Yu

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).

	//
	// Created by Florent Pillet on 14/11/16.
	// Copyright (c) 2016 Florent Pillet. All rights reserved.
	//

	import Foundation

	/*
	* A utility struct that helps mesure the performance of sections of code. Only uses Foundation
	* (we could also use QuartzCore's CACurrentMediaTime() for similar precision)

	//
	// SpinlockTestTests.swift
	// SpinlockTestTests
	//
	// Created by Peter Steinberger on 04/10/2016.
	// Copyright © 2016 PSPDFKit GmbH. All rights reserved.
	//

	import XCTest

	// WeakObjectSet.swift
	//
	// The MIT License (MIT)
	//
	// Copyright (c) 2020 Electricwoods LLC, Kaz Yoshikawa.
	//
	// Permission is hereby granted, free of charge, to any person obtaining a copy
	// of this software and associated documentation files (the "Software"), to deal
	// in the Software without restriction, including without limitation the rights
	// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

	// Release under MIT
	// Copyright (C) 2015 Xaree Lee

	#import <Foundation/Foundation.h>

	/* Get property name for the class (C string or NSSting). */
	#define keypathForClass(Klass, PropertyName) \
	(((void)(NO && ((void)[Klass _nullObjectForCheckingPropertyName].PropertyName, NO)), # PropertyName))
	#define keypathStringForClass(Klass, PropertyName) \
	@keypathForClass(Klass, PropertyName)

	func encode<T>(var value: T) -> NSData {
	return withUnsafePointer(&value) { p in
	NSData(bytes: p, length: sizeofValue(value))
	}
	}

	func decode<T>(data: NSData) -> T {
	let pointer = UnsafeMutablePointer<T>.alloc(sizeof(T.Type))
	data.getBytes(pointer)

100mango

libdispatch efficiency tips

Swift Concurrency Manifesto

Contents

OSX → macOS 10.12 Sierra

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	{
	[super viewWillAppear:animated];

	NSIndexPath *selectedRowIndexPath = [self.tableView indexPathForSelectedRow];
	if (selectedRowIndexPath) {
	[self.tableView deselectRowAtIndexPath:selectedRowIndexPath animated:YES];
	[[self transitionCoordinator] notifyWhenInteractionEndsUsingBlock:^(id<UIViewControllerTransitionCoordinatorContext> context) {
	if ([context isCancelled]) {
	[self.tableView selectRowAtIndexPath:selectedRowIndexPath animated:NO scrollPosition:UITableViewScrollPositionNone];