TweetFollow Us on Twitter

Libraries On The Mac

Volume Number: 14 (1998)
Issue Number: 6
Column Tag: Tools Of The Trade

Libraries on the Mac

by Jeremy Nelson

An overview of shared code mechanisms on the Macintosh

Libraries - precompiled collections of code - are a powerful tool for programmers. They allow us to distribute valuable technologies without disclosing the secrets of the proprietary source code from which those libraries were created. Because libraries are precompiled, they also encourage users of the technology to treat them as a black box - letting the user focus on their own code without worrying how library accomplishes its purpose. This article will survey library mechanisms on the Macintosh and offer a brief overview of the advantages of each.

Statically Linked Libraries

Libraries can be linked to other code statically or at runtime. A statically linked library, like code you have written yourself, is integrated into your application's binary during the compilation process. In contrast, a runtime library is loaded when the application executes, and calls made to the library are redirected to the loaded code. Both kinds of libraries are a good way to share new technologies.

Statically linked libraries are made up of a precompiled binary and an interface file which contains the API. Using a statically linked library is easy, simply include the binary and the C header file or Pascal interface file. During the linking stage of compilation the binary portion of the library is integrated into your application, exactly like the compiled code of the source you have written.

Most programs include some statically linked libraries. These libraries may provide language specific functions, basic Macintosh calls or mathematical functions.

Runtime Libraries

Runtime libraries, also known as Dynamically Linked Libraries (DLL), can reduce disk usage and lower memory requirements by allowing different applications to share a single copy of the code. Runtime libraries can also allow portions of an application to be selectively updated by simply replacing an old library file with a newer one.

Like statically linked libraries, runtime libraries are composed of a binary and an interface file. However the binary is simply a stub library which contains the names of the functions and version information. Mercifully, exactly how the functions are made available to your program when the program is executed is hidden from you. During your programs initialization phase, when your program is being readied to execute, the Operating System prepares any Shared Libraries you reference.

There are a variety of Shared Library mechanisms on the Mac, each with strengths and weakness. This diversity of library mechanisms exists largely due to historical factors. The formal library mechanisms are:

  • Apple Shared Library Manager (ASLM)
  • Code Fragment Manager (CFM and CFM-68K)
  • System Object Model (SOM)

For completeness, any discussion of shared code mechanisms also needs to include:

  • Component Manager
  • Code Resources

Custom mechanisms are also perfectly valid (if possibly application specific) ways of sharing code. Creating a custom mechanism allows developers to tailor a solution, but at the risk of recreating already tried and tested code- a somewhat ironic result.

Apple Shared Library Manager (ASLM)

ASLM is the one of the oldest solutions from Apple and it works under 68K and PPC. Unfortunately you can only make the libraries with MPW. While ASLM is available on every Mac and fairly straightforward to use, very little uses ASLM besides Open Transport 68K. Most programmers will never use ASLM directly.

Example: OpenTransport 68K.

Reference: ASLM Developer's Guide, Developer CD Series Mac OS SDK.

System Object Model (SOM)

SOM was developed by IBM to work on their AIX systems, runs under OS/2 and was ported to the Mac as part of the development of OpenDoc. SOM is both PowerPC and 68K and is probably the most technically advanced solution on the Macintosh. It is also a deprecated technology and as such it will probably not progress in the future.

SOM provides a number of desirable features. It can handle different calling conventions between caller and callee, and there are standard ways to patch and unpatch the code dynamically (so you can intercept a library call with your code). It even tackles the so-called 'fragile base class' problem and other changes to the interface of a library. SOM provides the calling program with full Object Oriented class libraries, even translating across different compilers' Object implementations.

While SOM is a technically wonderful solution it is a complex technology which has been quite difficult to use. Development tools have now reduced this difficulty somewhat. SOM was deprecated along with OpenDoc.

Examples: Opendoc and Cyberdog.

Reference: SOMobjects(tm) for Mac OS, Developer CD Series Mac OS SDK.

Code Fragment Manager (CFM and CFM-68K)

CFM was made specifically for PowerPC: when the PowerPC system came out there was no native shared library, so Apple developed a PowerPC native library format. CFM is used by both ASLM and SOM to load code fragments on the PowerPC.

In 1994 CFM was ported to 68K to provide a universal solution. CFM-68K had stability problems which discouraged its use for some time. This was fixed in version 4.0 of CFM-68K in November 1996 (as described in Technote 1084).

To use CFM-68K you need to use different versions of the runtime libraries, specially modified to work with CFM-68K. This makes your application a 'CFM-68K application', and you need to be careful about using custom preemptive threading methods (this problem relates to the version 4.0 bug fix mentioned above). (It is possible, but tricky, to call CFM-68K code from classic applications. See Technote 1077 for details.)

CFM is Apple's announced direction in shared code. There are good development tools for CFM in both CodeWarrior and MPW. If you were developing a library for a PowerPC application this should be your preferred choice. Under 68K some developers may be discouraged from adopting CFM-68K applications because of the changes necessary to their application.

Example: OpenTransport, MathLib, AppearanceLib.

References: IM PowerPC System Software, Chapter 3: Code Fragment Manager.

Component Manager

The Component Manager was written by the QuickTime team to meet their need for a universal plug-in architecture. As a result, the Component Manager is available under both 68K and PPC.

Components are code fragments with a particular type (like File Types in the file system). All components of the same type have the same interface. This allows applications to chose from a list of different code fragments, each of which may have different behaviour, but can be loaded and used identically. This is equivalent to having multiple different versions of a single library, each with different performance characteristics.

Components can also be captured which permits functions to be overridden and modified. A captured component is removed from the list of available components, but can still be called by the capturing component.

The drawback is that this added versatility introduces additional complexity. Applications must deal with selecting and loading the component: the code is not loaded automatically when the program is being loaded.

QuickTime is the most obvious user of the Component Manager. An interesting user of the Component Manager is Internet Config. When Internet Config was written this was the only solution which worked well under PowerPC and 68K, and provided the override functionality, which was a desired feature of Internet Config.

Examples: QuickTime, Internet Config.

Reference: IM More Toolbox, Chapter 6: Component Manager.

Code Resources

The most common example of code resources are List Definition Functions (LDEF), Window Definitions Functions (WDEF) and Control Definition Functions (CDEF). These are functions which are loaded using the Resource Manager. It is up to the programmer to define the API and the program is responsible for loading and unloading the code.

Typically Code Resources only have a single entry point (function call) with an argument which selects the actual function and a small number of other arguments, often contained in a parameter block. Which values are extracted from the parameter block may depend on what function is called.

Code Resources have been used in a number of applications and good example code is available. For instance, on the Code Warrior Pro 2 CD, the "Pascal Code Resources" shows how to create 68K or PPC code resources, either of which can be called from both 68K and PowerPC applications. (This is a useful way to update time-critical portions of a 68K application to run under PowerPC without updating the entire application.)

Examples: LDEFs, CDEFs, Codewarrior Plug-Ins under 68K.

Reference: IM More Toolbox, Chapter 1: Resource Manager.

Dangers

Probably the most confusing thing about libraries is that the binary can be compiled using a variety of different compiler options. Thus there are usually many different versions of any given library. For a splendid example of this, look in Codewarrior's MSL C:Bin folder. There are over a dozen different versions of the Metrowerks Standard C library (MSL C for 68K).

You need to make sure you include the appropriate version of the library in your code. You will not always get compiler warnings if you include the wrong version, and some mismatched program/library compiler settings can lead to intermittent errors which may be very difficult to debug.

There are several common compiler options unique to 68K which result in different versions. The main settings include:

  • Near or Far: Under 68K calls to functions can use so called 'Near' or 'Far' references.
  • 2i or 4i: Two or four byte integers. You need to be careful here since it is easy to include the wrong version, you will not get an error when the application is compiled, and it can result in obscure bugs which are hard to track down.

The PowerPC Runtime Architecture is much more precisely defined than under 68K. For example, under PowerPC all code references use the same convention and all integers are four bytes. As a result there are usually many fewer versions of the PowerPC library.

Different compilers can also generate different implementations of the same library. This is because the calling conventions for the functions (such as how the function parameters are ordered on the stack) are not generally defined by the language so it is up to the compiler vendors to choose. One good way around this is to export functions using the 'pascal' keyword. The Pascal calling conventions are well defined, so libraries compiled this way will work under different compilers and with different languages (all other options being equal).

It is also advisable to avoid the 'int' integer type in the library interface, instead use 'Int16' or 'Int32'. This gives more robustness across different compilers, languages and environments.

Conclusion

Libraries provide conceptually clean interfaces to code, which can be well tested and re-used. They can also lower compile time and allow large projects to be factored into smaller chunks. Runtime libraries provide additional benefits such as reduced disk and memory overhead, plus they can provide novel functionality through dynamic patching.

On the Macintosh under PowerPC the Code Fragment Manager is Apple's announced direction in shared code, has good tool support and is relatively easy to use. CFM is guaranteed to exist on all PowerPC Macs.

Unfortunately CFM-68K requires additional effort on behalf of programmers who wish to utilise CFM-68K libraries and CFM-68K support is not always present on older Macintoshes. For this reason Code Resources are often used as a relatively straightforward library mechanism.


Jeremy Nelson is a programmer and Technical Support Droid for Stairways Software Pty Ltd.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

iDefrag 5.1.7 - Disk defragmentation and...
iDefrag helps defragment and optimize your disk for improved performance. Features include: Supports HFS and HFS+ (Mac OS Extended). Supports case sensitive and journaled filesystems. Supports... Read more
TrailRunner 3.8.832 - Route planning for...
TrailRunner is the perfect companion for runners, bikers, hikers, and all people wandering under the sky. Plan routes on a geographical map. Import GPS or workout recordings and journalize your... Read more
VOX 2.8.14 - Music player that supports...
VOX just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features and support for all audio formats you should ever need.... Read more
WhiteCap 6.6 - Visual plug-in for iTunes...
WhiteCap is a sleek and sophisticated music visualizer and screensaver that features futuristic, wireframe mesh visuals with dynamic backgrounds and colors. WhiteCap contains thousands of visual... Read more
VueScan 9.5.65 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Carbon Copy Cloner 4.1.13 - Easy-to-use...
Carbon Copy Cloner backups are better than ordinary backups. Suppose the unthinkable happens while you're under deadline to finish a project: your Mac is unresponsive and all you hear is an ominous,... Read more
TrailRunner 3.8.831 - Route planning for...
TrailRunner is the perfect companion for runners, bikers, hikers, and all people wandering under the sky. Plan routes on a geographical map. Import GPS or workout recordings and journalize your... Read more
Quicken 4.4.2 - Complete personal financ...
Quicken makes managing your money easier than ever. Whether paying bills, upgrading from Windows, enjoying more reliable downloads, or getting expert product help, Quicken's new and improved features... Read more
Adobe Illustrator CC 2017 21.0.2 - Profe...
Illustrator CC 2017 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Illustrator customer). Adobe Illustrator CC 2017 is the industry... Read more
Paparazzi! 1.0b2 - Make user-defined siz...
Paparazzi! is a small utility for OS X that makes screenshots of webpages. This very simple tool takes screenshots of websites which do not fit on one screen. You specify the desired width, minimal... Read more

Last week on PocketGamer
Welcome to a weekly feature looking back on the past seven days of coverage on our sister website, PocketGamer. It’s taken a while for 2017 to really get going, at least when it comes to the world of portable gaming. Thank goodness, then, for... | Read more »
ROME: Total War - Barbarian Invasion set...
To the delight of mobile strategy fans, Feral Interactive released ROME: Total War just a few months ago. Now the game's expansion, Barbarian Invasion is marching onto iPads as a standalone release. [Read more] | Read more »
Yuri (Games)
Yuri 1.0 Device: iOS iPhone Category: Games Price: $3.99, Version: 1.0 (iTunes) Description: It's night. Yuri opens his eyes. He wakes up in a strange forest.The small, courageous explorer rides on his bed on casters in this... | Read more »
Space schmup Xenoraid launches on the Ap...
10Tons Xenoraid is out today on the App Store, bringing some high-speed space action to your mobile gadgets just in time for the weekend. The company's last premium title, another sci-fi game titled Neon Chrome, did quite well for itself, so... | Read more »
Star Wars: Force Arena Beginner's G...
Star Wars: Force Arena joined the populous ranks of Star Wars games on mobile today. It's a two-lane MOBA starring many familiar faces from George Lucas's famed sci-fi franchise. As with most games of this nature, Force Arena can be a little obtuse... | Read more »
Mysterium: The Board Game (Games)
Mysterium: The Board Game 1.0 Device: iOS Universal Category: Games Price: $6.99, Version: 1.0 (iTunes) Description: The official adaptation of the famous board game Mysterium! | Read more »
Sonny (Games)
Sonny 1.0.4 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.4 (iTunes) Description: Reimagined for iOS, cult-hit RPG Sonny brings challenging turn-based combat that requires strategy and mastery of each new skill to... | Read more »
Towaga (Games)
Towaga 1.0 Device: iOS iPhone Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: "It has been foretold that a masked being would stand atop the legendary Towaga Temple, dwelling among shadows to fulfil The Black Moon... | Read more »
Bubble Witch 3 Saga Guide: How to get th...
King's bringing its fairytale bubble-popping puzzler back for its 3rd outing in Bubble Witch 3 Saga. If you're familiar with the series, not much has changed here on the surface level, though you'll likely be pleased with the improvements. If you'... | Read more »
Sunless Sea sails onto iPad this spring
Failbetter Games, the folks who brought you Fallen London, are celebrating their 7th birthday today. To commemorate the event, the team revealed that Sunless Sea is coming to iPad this spring. | Read more »

Price Scanner via MacPrices.net

Opera Announces Neon Concept Browser For Mac
Opera is inviting users to get a glimpse of what Opera for computers could become with its Opera Neon browser concept. Each Opera Neon feature is described as “an alternate reality” for the Opera... Read more
Tellini Releases TabView 3.0 Missing Tool fo...
Tellini has announced the release of TabView 3.0. TabView has been the first macOS viewer for PowerTab tablatures. PowerTab is a well-known and widely adopted tablature editor for Windows systems and... Read more
13-inch 1.6GHz/128GB MacBook Air on sale for...
Overstock.com has the 1.6GHz/128GB 13″ MacBook Air on sale for $130 off MSRP including free shipping: - 13″ 1.6GHz/128GB MacBook Air (MMGF2LL/A): $869.99 $130 off MSRP Their price is the lowest... Read more
12-inch 32GB Space Gray iPad Pro on sale for...
B&H Photo has 12″ Space Gray 32GB WiFi Apple iPad Pros on sale for $55 off MSRP including free shipping. B&H charges sales tax in NY only: - 12″ Space Gray 32GB WiFi iPad Pro: $744.44 $55 off... Read more
9-inch 32GB Space Gray iPad Pro on sale for $...
B&H Photo has the 9.7″ 32GB Space Gray Apple iPad Pro on sale for $549 for a limited time. Shipping is free, and B&H charges NY sales tax only. Read more
Apple iMacs on sale for up to $120 off MSRP,...
B&H Photo has 21″ and 27″ Apple iMacs on sale for up to $120 off MSRP, each including free shipping plus NY sales tax only: - 27″ 3.3GHz iMac 5K: $2199 $100 off MSRP - 27″ 3.2GHz/1TB Fusion iMac... Read more
Apple refurbished Apple TVs available for up...
Apple has Certified Refurbished 32GB and 64GB Apple TVs available for up to $30 off the cost of new models. Apple’s standard one-year warranty is included with each model, and shipping is free: -... Read more
1.4GHz Mac mini, refurbished, available for $...
The Apple Store has Apple Certified Refurbished 1.4GHz Mac minis available for $419. Apple’s one-year warranty is included, and shipping is free. Their price is $80 off MSRP, and it’s the lowest... Read more
16GB iPad Air 2, Apple refurbished, available...
Apple has Certified Refurbished 16GB iPad Air 2s available for $319 including free shipping. A standard Apple one-year is included. Their price is $60 off original MSRP for this model. Read more
Mac Pros on sale for $200 off MSRP, refurbish...
B&H Photo has Mac Pros on sale for $200 off MSRP. Shipping is free, and B&H charges sales tax in NY only: - 3.7GHz 4-core Mac Pro: $2799, $200 off MSRP - 3.5GHz 6-core Mac Pro: $3799, $200... Read more

Jobs Board

*Apple* Retail - Multiple Positions- Crows N...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* & PC Desktop Support Technician...
Apple & PC Desktop Support Technician job in Los Angeles, CA Introduction: We have immediate job openings for several Desktop Support Technicians with one of our Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Premier Retailer - PT Service Specia...
DescriptionSimply Mac is the largest premier retailer for Apple products and solutions. At Simply Mac we are all Apple , all the time. Same products. Same prices. Read more
*Apple* Premier Retailer - Service Manager -...
DescriptionSimply Mac is the largest premier retailer for Apple products and solutions. At Simply Mac we are all Apple , all the time. Same products. Same prices. Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.