Jonas Due Vesterheden jdv85

This is an excerpt from our internal documentation describing an issue with drawing in NSViews on macOS Big Sur.

1️⃣ Introduction

In macOS Big Sur (probably starting with β9), Apple changed the default contents format for backing layers of NSViews. Instead of an explicit CALayerContentsFormat.RGBA8Uint value, an „Automatic“ value is now used. Even though it also resolves into „RGBA8“ in our testing, it has some serious implications as it breaks assumptions our code relies on.

I first stumbled upon this issue in this tweet by Frank. It links to a thread on Apple Forums by Mark that contains valuable information as well as ideas for workarounds. The changed behavior was also confirmed by Marcin in this tweet.

2️⃣ Impact on Diagrams

Diff output of two lldb commands

Setup

Copy the contents of the last snippet (lldbinit) from the gist page, and paste into your .lldbinit file. This makes the ksdiff macro known inside lldb.
Put file ksdiff.py in ~/.lldb/
sudo pip install temp
Restart Xcode debug session

Example

(lldb) ksdiff ;

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

NOTE (2022-07-09): Xcode finally added this functionality in Xcode 14, please see release notes here:

New Features in Xcode 14 Beta 3
When editing code, the Edit > Duplicate menu item and its corresponding keyboard shortcut now duplicate the selected text — or the line that currently contains the insertion point, if no text is selected. (8614499) (FB5618491)

	#!/bin/bash

	# WARNING: still does not match against the usb. Needs to be further debugged with other pojects to find out what is wrong

	VENDOR_ID_HEX=0xB27
	VENDOR_ID_DEC=2855
	PRODUCT_ID_HEX=0x603
	PRODUCT_ID_DEC=1539

	# Find your device IDs

	// cc reenumerate.c -framework IOKit -framework CoreFoundation -o reenumerate
	#include <stdio.h>
	#include <CoreFoundation/CoreFoundation.h>
	#include <IOKit/IOKitLib.h>
	#include <IOKit/IOCFPlugIn.h>
	#include <IOKit/usb/IOUSBLib.h>
	#include <mach/mach.h>

	#define kExcAccMaxWait 5

	#!/bin/bash

	SERVICE_NAME='my-example-vpn'
	SERVICE_URL='my-example-vpn.com'

	if [[ ${#USER} > 1 ]]
	then
	read -p "Log in as ${USER}? [y/n] " LIA
	else
	LIA = 'n'

	/// 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

	/*
	File: ExceptionTest.c

	Contains: Test code for Mach exception handling.

	Written by: DTS

	Copyright: Copyright (c) 2006 by Apple Computer, Inc., All Rights Reserved.

	Disclaimer: IMPORTANT: This Apple software is supplied to you by Apple Computer, Inc.