Matteo Crespi mttcrsp

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

	//
	// A Swift property wrapper for adding "indirect" to struct properties.
	// Enum supports this out of the box, but for some reason struct doesn't.
	//
	// This is useful when you want to do something recursive with structs like:
	//
	// struct Node {
	// var next: Node?
	// }
	//

	import Darwin
	import Foundation
	import UIKit

	// https://github.com/xybp888/iOS-SDKs/blob/master/iPhoneOS17.1.sdk/System/Library/PrivateFrameworks/CoreSVG.framework/CoreSVG.tbd
	// https://developer.limneos.net/index.php?ios=17.1&framework=UIKitCore.framework&header=UIImage.h

	@objc
	class CGSVGDocument: NSObject { }

	// NSCalendar+Swift.swift
	// A set of Swift-idiomatic methods for NSCalendar
	//
	// (c) 2015 Nate Cook, licensed under the MIT license

	extension NSCalendar {
	/// Returns the hour, minute, second, and nanoseconds of a given date.
	func getTimeFromDate(date: NSDate) -> (hour: Int, minute: Int, second: Int, nanosecond: Int) {
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	/// Observes a run loop to detect any stalling or blocking that occurs.
	///
	/// This class is thread-safe.
	@interface GHRunLoopWatchdog : NSObject

	/// Initializes the receiver to watch the specified run loop, using a default
	/// stalling threshold.
	- (id)initWithRunLoop:(CFRunLoopRef)runLoop;

	/// Initializes the receiver to detect when the specified run loop blocks for

	extension NSTimer {
	/**
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	- Parameters:
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	*/

	#!/bin/sh

	UNIVERSAL_OUTPUTFOLDER=${BUILD_DIR}/${CONFIGURATION}-universal

	# make sure the output directory exists
	mkdir -p "${UNIVERSAL_OUTPUTFOLDER}"

	# Step 1. Build Device and Simulator versions
	xcodebuild -target "${PROJECT_NAME}" ONLY_ACTIVE_ARCH=NO -configuration ${CONFIGURATION} -sdk iphoneos BUILD_DIR="${BUILD_DIR}" BUILD_ROOT="${BUILD_ROOT}" clean build
	xcodebuild -target "${PROJECT_NAME}" -configuration ${CONFIGURATION} -sdk iphonesimulator ONLY_ACTIVE_ARCH=NO BUILD_DIR="${BUILD_DIR}" BUILD_ROOT="${BUILD_ROOT}" clean build

	#import "UICollectionViewFlowLayoutCenterItem.h"

	@implementation UICollectionViewFlowLayoutCenterItem

	- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity
	{
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	/** @jsx React.DOM */
	var MyComponent = React.createClass({
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	return {perMinute: '-', perDay: '-'};
	},
	componentDidMount: function() {
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	// used for initialization code that has "side effects" i.e. i/o, jquery plugins, etc
	var socket = io.connect(this.props.url);