TweetFollow Us on Twitter

Apr 01 ADC Direct Volume Number: 17 (2001)
Issue Number: 4
Column Tag: ADC Direct

Darwin: Mac OS X’s Core OS

By John Signa

Beneath Mac OS X's user-friendly and attractive user interface, Aqua, and the application frameworks (Classic, Carbon and Cocoa) is Darwin: Mac OS X's core OS. Unseen by users, Darwin provides a strong yet flexible foundation with features like preemptive multitasking, protected memory and real-time support that make Mac OS X a truly modern operating system.

The focus of this article is to provide a brief overview of Darwin and its components as well as give an introduction to developing kernel extensions-modules that extend Darwin's functionality. For more in-depth information, you should read Inside Mac OS X: Kernel Environment which is available, along with other documents referred to in this article, on the Apple Developer Connection (ADC) web site in the Mac OS X Documentation section:

http://developer.apple.com/techpubs/macosx/macosx.html

ADC Programs and Mac OS X

Register today for Apple’s Worldwide Developers Conference (WWDC) from May 21-25, 2001 in San Jose, California. WWDC will feature more than 100 in-depth technical sessions and hands-on labs. You’ll have access to Apple engineers and technology experts to answer your software and hardware development questions.

Naturally, WWDC 2001 session topics will cover a full range of Apple development subjects: Mac OS X architecture (Darwin, Quartz, OpenGL, QuickTime, Carbon, Cocoa, Aqua), hardware, BSD UNIX, Java, WebObjects, development tools and much more.

Register now to attend the conference, network with peers and learn about all of the exciting technologies designed in Mac OS X. Pricing, detailed session information and registration information is available at:

http://www.apple.com/developer/wwdc2001/

Remember, ADC Select and Premier members receive special discounts. See you in May!

Most of the reference documents can be found in the /Developer/Documentation/ Kernel directory on any Mac OS X system with the Mac OS X Developer Tools package installed.

Components of Darwin

Just like in the old Reese's Peanut Butter Cups commercials ("You've got chocolate in my peanut butter... No, you've got peanut butter on my chocolate!"), Darwin blends a mixture of mature industry standard components such as Mach and BSD with Apple-engineered components to provide Mac OS X with a stable, reliable and extensible foundation. Darwin consists of five main components: Mach, I/O Kit, File System, Networking and BSD.

Mach

At the heart of Darwin is Mach, based on Mach 3.0 from Carnegie Mellon University. Mach manages processor resources such as CPU usage and memory, handles scheduling, provides memory protection and provides a messaging-centered infrastructure to the rest of the operating system layers. Mach provides Mac OS X with protected memory, preemptive multitasking, virtual memory and real-time support.

I/O Kit

Darwin provides an object-oriented framework, I/O Kit, for the development of device drivers. I/O Kit not only facilitates the creation of drivers for Mac OS X but also provides much of the infrastructure that drivers require. It consists of three major components: families, nubs and drivers.

A family defines a collection of software abstractions that are common to all devices of a particular category. Apple provides families for protocols such as USB, SCSI and FireWire, as well as for devices such as storage, HID and frame buffers. Mac OS X developers should rely upon these provided families-not create new families.

A nub is an I/O object that represents a device or logical service. A nub may represent a bus, a disk, a disk partition, a keyboard or any number of similar entities.

A driver is an object that manages a specific piece of hardware, implementing the appropriate I/O Kit abstractions for controlling that hardware. Mac OS X provides a collection of drivers that handle standard devices such as hard drives and human input devices. If your device complies with an industry standard but has additional functionality, then you simply need to subclass the provided driver and implement just the code that handles the uniqueness of your device.

Anyone working with I/O Kit-either as an application writer or a driver developer-should read Inside Mac OS X: I/O Kit Architecture to get more background on how I/O Kit works. Device driver developers should also read Mac OS X: Writing I/O Kit Drivers. Application developers should read Inside Mac OS X: Accessing Hardware from Applications. Both documents are available on the ADC web site in the Mac OS X Documentation section.

File System

The file system component of Darwin is based on an enhanced Virtual File System (VFS) design, which provides the ability to add in new file systems and enhance those already supported, including HFS, HFS+ UFS, and ISSO 9660. VFS stacks also allow you to create and layer new capabilities, such as file-based compression or encryption onto an existing file system type.

Networking

Mac OS X also provides an extensible networking system. By implementing Network Kernel Extensions (NKEs) developers can add support for additional networking protocols as well as enhance the networking functionality already provided. Developers who need to extend Mac OS X's networking capabilities should read Inside Mac OS X: Network Kernel Extensions for more details.

BSD

Darwin wraps a customized version of BSD 4.4 around the kernel. Darwin's implementation of BSD includes many of the POSIX APIs, exporting them to user-space, and abstracts Darwin's file system and networking. Darwin's BSD also provides Mac OS X's process model, basic security policies and threading support.

For developers, the biggest advantage of Darwin's BSD implementation is that it enables you to quickly port UNIX-style applications to Mac OS X. In some cases, developers have had their UNIX applications up and running on Mac OS X in a matter of hours. Because BSD does not provide GUI APIs, you will need to create a Carbon or Cocoa application to handle the user interface. Much of this work can be done using Interface Builder, Apple's user interface design tool available on the Mac OS X Developer Tools CD.

Developing Kernel Extensions

To handle enhancements to the kernel, Mac OS X provides the ability to dynamically load pieces of code, referred to as Kernel Extensions (KEXTs), without needing to recompile the kernel. All kernel extensions are implemented as "bundles"-folders that the Finder treats as single entities. In addition to having names that end in ".kext," all kernel extensions contain a property list (plist), which is an XML text file describing the KEXT's contents and requirements. Additionally, a KEXT will usually, but not always, include a module (KMOD) that contains the binary code that is actually loaded into the kernel and run. A KEXT can also contain additional resources such as icons for the Finder.

Before you dive into developing a KEXT, you must decide if you really need to run in the kernel space. Compared to code running at the user space, kernel extensions are more difficult to write and debug. Furthermore, bugs in kernel extensions can have far more severe consequences. For example, a memory access error in a user application can, at worst, cause that application to crash yet leave the rest of the OS functional. In contrast, a memory access error in a KEXT causes a system panic, crashing the entire operating system.

Project Builder Tips & Tricks

  • Regular expression searches are very powerful. If you use regular expressions with subexpressions, you can reference the subexpressions in your replace string using "\#" syntax where "#" is the index of the subexpression. For example, if you search for the regular expression "foo(.*)bar" and find an occurrence with is "fooabcdbar," a replace string of "bar\1foo" will change that match into "barabcdfoo."
  • Find Options Sets can make your batch searches much faster. Try defining a set that does not search framework headers and one that only searches framework headers, and swap between them depending on what you're looking for.
  • Lots of cool features are only available if you index your project. You have to index a project manually, the first time. After that, your index will be kept up to date automatically.

New Mac OS X Related Releases

The following software is available from the Download Software area of the ADC Member Site at: http://connect.apple.com/

  • CarbonLib 1.2.5 GM SDK
    The CarbonLib 1.2.5 SDK for Mac OS is now available to all developers. This SDK provides all the files needed to begin Carbon development. CarbonLib 1.2.5 supports Mac OS 8.6 and greater.
    http://developer.apple.com/technical/
  • CarbonLib 1.3d6 SDK
    The latest prerelease version of the CarbonLib 1.3 SDK for Mac OS is now available to all ADC Members.
    http://developer.apple.com/technical/

Developer Documentation

The following new and updated documentation is available to help you on your way to successful Mac OS X application and peripheral development at: http://developer.apple.com/techpubs/

  • iMac Developer Note (Update)
  • Inside Cocoa: Object-Oriented Programming and the Objective-C Language
  • Mac OS X: An Overview for Developers - A 10-page PDF document that explains the unique combination of technologies in Mac OS X and discusses the benefits of those technologies to developers.
    http://developer.apple.com/macosx/

TN1191 - USB Software Locator

QA1008 - WaitMouseUp documentation errata QA1001 - Detecting CD/DVD media types QA1006 - Displaying Help QA1005 - Open File Limits on Mac OS X QA1004 - Displaying the device tree in Mac OS X QA1003 - Enabling Macintosh-style Menu Bars

SAMPLECODE - QuickTime: Importers and Exporters: ElectricImageComponent SAMPLECODE - Human Interface Toolbox: ScrollingTextUserPane SAMPLECODE - Human Interface Toolbox: MLTEEditField SAMPLECODE - Human Interface Toolbox: HTMLUserPane SAMPLECODE - Human Interface Toolbox: HandyScrollingSample SAMPLECODE - Networking: URLAccessSample SAMPLECODE - Files: MoreFiles SAMPLECODE - Printing: PostScript Output Filters SAMPLECODE - Java: JNISample SAMPLECODE - Human Interface Toolbox: CarbonCustomList SAMPLECODE - Networking: OTLookupNameTest

Upcoming Seminars and Events

For more information on Apple developer events please visit the developer Events page at: http://developer.apple.com/events/

Training and Seminars

Programming with Cocoa
Taught by Aaron Hillegass at the Big Nerd Ranch, Ashville, NC and Atlanta, GA. Five-day classes are taught on developing web-based and Mac OS X applications. http://www.bignerdranch.com/when.html

Developer Related Conferences

National Association of Broadcasters (NAB) Conference,
Las Vegas, NV
April 21-26

Produced annually by the National Association of Broadcasters, NAB2001 is the world's leading conference and exhibition for the converging electronic media communications industries. Apple will be exhibiting in Booth #M9131. http://www.nab.org/conventions/nab2001/

Worldwide Developers Conference (WWDC) 2001,
San Jose, CA
May 21-25

Register now for Apple’s Worldwide Developers Conference 2001, which takes place in San Jose, California from May 21-25. ADC Premier members receive a free pass to the conference and ADC Select members receive discounts for early registration. For schedules and other details check out: http://www.apple.com/developer/wwdc2001/

MacHack Conference, Dearborn, MI
June 21-23

MacHack, in its sixteenth year, remains centered around cutting edge software development. MacHack's uniqueness derives from the informal feel and the LIVE coding that occurs around-the-clock during the conference. http://www.machack.com/

When you are trying to decide if a piece of code should be a KEXT, the answer is generally no. Just because your code was a system extension in Mac OS 8 or 9, does not mean that it must necessarily be a kernel extension in Mac OS X. To help you decide, ask yourself the following questions:

  • Does your code need to take a primary interrupt? That is, does something in the hardware need to interrupt the CPU?
  • Does the primary client of your code reside inside the kernel (for example, a hard drive whose primary client is the file system)?
  • Do a sufficiently large number of running applications require a resource that your code provides (for example, a file-system stack)?

If you answered "no" to all of the above, then you should consider developing your code as a library or a background application rather than as a kernel extension. You might also consider using one of the user level plug-in architectures provided by Mac OS X, such as QuickTime components or Printer Modules. However, if you are writing device drivers or code to support a new volume format or networking protocol, KEXTs may be the only solution.

Fortunately, while KEXTs are more difficult to write than user-space code, several tools and procedures are available to enhance the development and debugging process. Currently you'll need to use Apple's Project Builder IDE to create KEXTs and use GDB for debugging. For a quick introduction on creating and debugging KEXTs with Project Builder GDB, you should read Inside Mac OS X:Kernel Extensions Tutorial.

Open Source

In March, 1999, Apple announced the Darwin Open Source initiative, making Apple the first major computer company to make open-source development a key part of its ongoing software strategy. Apple has released the source code to virtually all of the components of Darwin to the developer community, providing you the ability to see how Apple has implemented Mac OS X's core OS. Not only is this helpful in understanding how the OS works, but it also allows you to utilize portions of Darwin within your own products. Before doing so you should review the Apple Public Source License to understand the limitations or obligations this entails. It can be found at:

http://opensource.apple.com/apsl/

Summary

Developing kernel code is never trivial, however Darwin's flexible architecture makes it easier than ever before to write drivers or add additional file systems for Mac OS X. By implementing such a flexible architecture in Darwin, Apple has provided a foundation that delivers the reliability and performance you'd expect from a modern operating system. Moreover, releasing Darwin to the open source community ensures that it will continue to evolve as a high-quality, interoperable system built on open standards.


John Signa is the Technology Manager for Mac OS X Core OS in Apple Worldwide Developer Relations. John first got involved in the Macintosh industry in 1988 writing software for Orange Micro's printing products. He later spent three years at SuperMac/Radius writing display and video drivers.

Did You Know?

Darwin: Document It!

You probably know that you can go to Apple's Open Source web site (www.opensource. apple.com) and download the binary and source code of Darwin and other Open Source projects. But did you know that you can get more than code? You can also obtain documentation as well. And you can add to this store of information.

That's because this documentation is created by developers in the Apple Open Source community for other developers. The Darwin Documentation project (also at www.opensource.apple.com) provides you with an assortment of tools and guides to help you compose professional-looking documents. These documents are of three types:

  • HeaderDoc-Reference documentation produced by a Perl tool that parses structured commentary embedded in C and C++ header files and produces rich HTML output from that commentary.
  • HOWTO documents-Conceptual and task-oriented information on specific programming topics. HOWTO documents are based on DocBook XML because from this format tools can process the document into multiple formats (HTML, PDF, etc.). The documentation project provides a template and instructions for creating HOWTO documents. You don't have to learn DocBook XML if you don't want to; you can submit the HOWTO as an HTML document and Apple will convert it to XML.
  • Manpages-Traditional UNIX-style documentation of command-line tools and utilities.

"Built of Mac OS X" Badge Now Available

Tell the world your product runs on Mac OS X! The artwork, licensing requirements and guidelines for use of the new “Built for Mac OS X” badge are now available on the ADC Software Licensing web site. Please note that this badge cannot be used for products that launch the Classic environment.

http://developer.apple.com/mkt/swl/agreements.html#macosx
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

FotoMagico 5.6.12 - Powerful slideshow c...
FotoMagico lets you create professional slideshows from your photos and music with just a few, simple mouse clicks. It sports a very clean and intuitive yet powerful user interface. High image... Read more
OmniGraffle Pro 7.12.1 - Create diagrams...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
beaTunes 5.2.1 - Organize your music col...
beaTunes is a full-featured music player and organizational tool for music collections. How well organized is your music library? Are your artists always spelled the same way? Any R.E.M. vs REM?... Read more
HandBrake 1.3.0 - Versatile video encode...
HandBrake is a tool for converting video from nearly any format to a selection of modern, widely supported codecs. Features Supported Sources VIDEO_TS folder, DVD image or real DVD (unencrypted... Read more
Macs Fan Control 1.5.1.6 - Monitor and c...
Macs Fan Control allows you to monitor and control almost any aspect of your computer's fans, with support for controlling fan speed, temperature sensors pane, menu-bar icon, and autostart with... Read more
TunnelBear 3.9.3 - Subscription-based pr...
TunnelBear is a subscription-based virtual private network (VPN) service and companion app, enabling you to browse the internet privately and securely. Features Browse privately - Secure your data... Read more
calibre 4.3.0 - Complete e-book library...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
Lyn 1.13 - Lightweight image browser and...
Lyn is a fast, lightweight image browser and viewer designed for photographers, graphic artists, and Web designers. Featuring an extremely versatile and aesthetically pleasing interface, it delivers... Read more
Visual Studio Code 1.40.0 - Cross-platfo...
Visual Studio Code provides developers with a new choice of developer tool that combines the simplicity and streamlined experience of a code editor with the best of what developers need for their... Read more
OmniGraffle 7.12.1 - Create diagrams, fl...
OmniGraffle helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use Graffle to... Read more

Latest Forum Discussions

See All

The House of Da Vinci 2 gets a new gamep...
The House of Da Vinci launched all the way back in 2017. Now, developer Blue Brain Games is gearing up to deliver a second dose of The Room-inspired puzzling. Some fresh details have now emerged, alongside the game's first official trailer. [Read... | Read more »
Shoot 'em up action awaits in Battl...
BattleBrew Productions has just introduced another entry into its award winning, barrelpunk inspired, BattleSky Brigade series. Whilst its previous title BattleSky Brigade TapTap provided fans with idle town building gameplay, this time the... | Read more »
Arcade classic R-Type Dimensions EX blas...
If you're a long time fan of shmups and have been looking for something to play lately, Tozai Games may have just released an ideal game for you on iOS. R-Type Dimensions EX brings the first R-Type and its sequel to iOS devices. [Read more] | Read more »
Intense VR first-person shooter Colonicl...
Our latest VR obsession is Colonicle, an intense VR FPS, recently released on Oculus and Google Play, courtesy of From Fake Eyes and Goboogie Games. It's a pulse-pounding multiplayer shooter which should appeal to genre fanatics and newcomers alike... | Read more »
PUBG Mobile's incoming update bring...
PUGB Mobile's newest Royale Pass season they're calling Fury of the Wasteland arrives tomorrow and with it comes a fair chunk of new content to the game. We'll be seeing a new map, weapon and even a companion system. [Read more] | Read more »
PSA: Download Bastion for free, but wait...
There hasn’t been much news from Supergiant Games on mobile lately regarding new games, but there’s something going on with their first game. Bastion released on the App Store in 2012, and back then it was published by Warner Bros. This Warner... | Read more »
Apple Arcade: Ranked - 51+ [Updated 11.5...
This is Part 2 of our Apple Arcade Ranking list. To see part 1, go here. 51. Patterned [Read more] | Read more »
NABOKI is a blissful puzzler from acclai...
Acclaimed developer Rainbow Train's latest game, NABOKI, is set to launch for iOS, Android, and Steam on November 13th. It's a blissful puzzler all about taking levels apart in interesting, inventive ways. [Read more] | Read more »
A Case of Distrust is a narrative-driven...
A Case of Distrust a narrative-focused mystery game that's set in the roaring 20s. In it, you play as a detective with one of the most private eye sounding names ever – Phyllis Cadence Malone. You'll follow her journey in San Francisco as she... | Read more »
Brown Dust’s October update offers playe...
October is turning out to be a productive month for the Neowiz team, and a fantastic month to be a Brown Dust player. First, there was a crossover event with the popular manga That Time I Got Reincarnated as a Slime. Then, there was the addition of... | Read more »

Price Scanner via MacPrices.net

Score a 37% discount on Apple Smart Keyboards...
Amazon has Apple Smart Keyboards for current-generation 10″ iPad Airs and previous-generation 10″ iPad Pros on sale today for $99.99 shipped. That’s a 37% discount over Apple’s regular MSRP of $159... Read more
Apple has refurbished 2019 13″ 1.4GHz MacBook...
Apple has a full line of Certified Refurbished 2019 13″ 1.4GHz 4-Core Touch Bar MacBook Pros available starting at $1099 and up to $230 off MSRP. Apple’s one-year warranty is included, shipping is... Read more
2019 13″ 1.4GHz 4-Core MacBook Pros on sale f...
Amazon has new 2019 13″ 1.4GHz 4-Core Touch Bar MacBook Pros on sale for $150-$200 off Apple’s MSRP. These are the same MacBook Pros sold by Apple in its retail and online stores: – 2019 13″ 1.4GHz/... Read more
11″ 64GB Gray WiFi iPad Pro on sale for $674,...
Amazon has the 11″ 64GB Gray WiFi iPad Pro on sale today for $674 shipped. Their price is $125 off MSRP for this iPad, and it’s the lowest price available for the 64GB model from any Apple reseller. Read more
2019 15″ MacBook Pros available for up to $42...
Apple has a full line of 2019 15″ 6-Core and 8-Core Touch Bar MacBook Pros, Certified Refurbished, available for up to $420 off the cost of new models. Each model features a new outer case, shipping... Read more
2019 15″ MacBook Pros on sale this week for $...
Apple resellers B&H Photo and Amazon are offering the new 2019 15″ MacBook Pros for up to $300 off Apple’s MSRP including free shipping. These are the same MacBook Pros sold by Apple in its... Read more
Sunday Sale: AirPods with Wireless Charging C...
B&H Photo has Apple AirPods with Wireless Charging Case on sale for $159.99 through 11:59pm ET on November 11th. Their price is $40 off Apple’s MSRP, and it’s the lowest price available for these... Read more
Details of Sams Club November 9th one day App...
Through midnight Saturday night (November 9th), Sams Club online has several Apple products on sale as part of their One Day sales event. Choose free shipping or free local store pickup (if available... Read more
Sprint is offering the 64GB Apple iPhone 11 f...
Sprint has the new 64GB iPhone 11 available for $15 per month for new lines. That’s about 50% off their standard monthly lease of $29.17. Over is valid until November 24, 2019. The fine print: “Lease... Read more
New Sprint November iPhone deal: Lease one iP...
Switch to Sprint and purchase an Apple iPhone 11, 11 Pro, or 11 Pro Max, and get a second 64GB iPhone 11 for free. Requires 2 new lines or 1 upgrade-eligible line and 1 new line. Offer is valid from... Read more

Jobs Board

*Apple* Mobility Pro - Best Buy (United Stat...
**746087BR** **Job Title:** Apple Mobility Pro **Job Category:** Store Associates **Store NUmber or Department:** 000319-Harlem & Irving-Store **Job Description:** Read more
Best Buy *Apple* Computing Master - Best Bu...
**743392BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Store Associates **Store NUmber or Department:** 001171-Southglenn-Store **Job Read more
Best Buy *Apple* Computing Master - Best Bu...
**746015BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Sales **Store NUmber or Department:** 000372-Federal Way-Store **Job Description:** Read more
*Apple* Mobility Pro - Best Buy (United Stat...
**744658BR** **Job Title:** Apple Mobility Pro **Job Category:** Store Associates **Store NUmber or Department:** 000586-South Hills-Store **Job Description:** At Read more
Best Buy *Apple* Computing Master - Best Bu...
**741552BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Sales **Store NUmber or Department:** 000277-Metcalf-Store **Job Description:** **What Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.