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

CleanMyMac 3.9.2 - $39.95
CleanMyMac makes space for the things you love. Sporting a range of ingenious new features, CleanMyMac lets you safely and intelligently scan and clean your entire system, delete large, unused files... Read more
Printopia 3.0.4 - Share Mac printers wit...
Run Printopia on your Mac to share its printers to any capable iPhone, iPad, or iPod Touch. Printopia will also add virtual printers, allowing you to save print-outs to your Mac and send to apps.... Read more
Tinderbox 7.3.1 - Store and organize you...
Tinderbox is a personal content management assistant. It stores your notes, ideas, and plans. It can help you organize and understand them. And Tinderbox helps you share ideas through Web journals... Read more
ExpanDrive 6.1.6 - Access cloud storage...
ExpanDrive builds cloud storage in every application, acts just like a USB drive plugged into your Mac. With ExpanDrive, you can securely access any remote file server directly from the Finder or... Read more
Printopia 3.0.4 - Share Mac printers wit...
Run Printopia on your Mac to share its printers to any capable iPhone, iPad, or iPod Touch. Printopia will also add virtual printers, allowing you to save print-outs to your Mac and send to apps.... Read more
Tinderbox 7.3.1 - Store and organize you...
Tinderbox is a personal content management assistant. It stores your notes, ideas, and plans. It can help you organize and understand them. And Tinderbox helps you share ideas through Web journals... Read more
ExpanDrive 6.1.6 - Access cloud storage...
ExpanDrive builds cloud storage in every application, acts just like a USB drive plugged into your Mac. With ExpanDrive, you can securely access any remote file server directly from the Finder or... Read more
VOX 3.0.1 - Music player that supports m...
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
Merlin Project 4.3.3 - $289.00
Merlin Project is the leading professional project management software for OS X. If you plan complex projects on your Mac, you won’t get far with a simple list of tasks. Good planning raises... Read more
Mac DVDRipper Pro 7.1 - Copy, backup, an...
Mac DVDRipper Pro is the DVD backup solution that lets you protect your DVDs from scratches, save your batteries by reading your movies from your hard disk, manage your collection with just a few... Read more

Latest Forum Discussions

See All

Animal Crossing: Pocket Camp mid-game gu...
By this point, you've probably hit or surpassed mid-way inAnimal Crossing: Pocket Camp.The game changes quite a bit as your focus slowly shifts from endlessly fulfilling requests for campsite buddies to improving your amenities. Here are a few tips... | Read more »
Mille Bornes (Games)
Mille Bornes 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: | Read more »
Blob gets a new look in Give It Up! 3
Blob makes his triumphant return, as Yoozoo Games and Invictus Gaming have joined forces to create Give It Up! 3, the third in a series of delightful action-adventure games featuring our wobbly friend Blob. In this newest adventure, you’ll get to... | Read more »
148Apps' Ultimate Guide to Black Fr...
Black Friday is here, and there are a whole lot of discounts running right now for folks on the lookout for new mobile devices, accessories, and yes, even games. Here's a helpful rundown of what you'll find both in stores and online. Happy... | Read more »
The best Black Friday mobile game deals
Black Friday's upon us, and if you've happened to nab a fancy new phone during the week's big savings, you might be searching for some new games to fill up space on your new gadget. There are a lot of great games on sale right now for Black Friday... | Read more »
The best mobile games to play while your...
Thanksgiving is a time to reconnect with loved ones, eat lots of food, and all of that jazz, but once the festivities start to wind down, folks tend to head to the couch to watch whatever football is happening for Turkey Day. | Read more »
The best Black Friday deals for Apple ga...
Black Friday is hours away at this point, but many popular retailers are getting a jump on things with plenty of pre-Black Friday sales already available. Many of those early bird sales including some sharp discounts on the latest Apple phones... | Read more »
The Inner World 2 (Games)
The Inner World 2 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Solve mind-bending puzzles in a world full of mystery and save the family of the flute-noses! Their dynasty has been... | Read more »
warbot.io wants you for the robot wars
Fans of epic gundam-style battles will find a lot to love in warbot.io, the first game for up and coming developer Wondersquad. The game saw a lot of success when it first launched for browsers and Facebook, and now even more people are getting the... | Read more »
Uncover alien mysteries in cross-genre s...
If the Alien franchise taught us anything, it’s that landing on a strange planet at the behest of a faceless corporation is probably asking for trouble. And Eldritch Game’s Deliria doesn’t prove otherwise. In 2107, Dimension LG7 is rich with... | Read more »

Price Scanner via MacPrices.net

Apple 9″ 32GB iPad for $80 off on Walmart onl...
Snag a 9.7″ 32GB WiFi iPad for $249 on Walmart’s online store as part of their Black Friday sale. That’s $80 off MSRP, and it’s the lowest price available for an iPad so far this season. Sale price... Read more
Apple Black Friday sale for 2017: $150 Apple...
BLACK FRIDAY Apple has posted their Black Friday deals for 2017. Receive a $150 Apple gift card with the purchase of select Macs and up to $100 with various iPads, iPhones, and Apple Watches. The... Read more
Black Friday 2017: Where to find the best dea...
B&H Photo has 15″ and 13″ MacBook Pros on sale for up to $200 off MSRP as part of the Black Friday and Holiday sale. Shipping is free, and B&H charges sales tax for NY & NJ residents only... Read more
Black Friday 2017: Where to find the best dea...
B&H Photo has 12″ MacBooks on sale for $150 off MSRP as part of the Black Friday and Holiday sale. Shipping is free, and B&H charges sales tax for NY & NJ residents only: – 12″ 1.2GHz... Read more
Black Friday 2017: Where to find the best dea...
B&H Photo has 10.5″ iPad Pros in stock today and on sale for up to $130 off MSRP. Each iPad includes free shipping, and B&H charges sales tax in NY & NJ only: – 10.5″ 64GB WiFi iPad Pro... Read more
Black Friday 2017: Where to find the best dea...
B&H Photo has 13″ MacBook Airs on sale for up to $150 off MSRP as part of the Black Friday and Holiday sale. Shipping is free, and B&H charges sales tax for NY & NJ residents only: – 13″... Read more
Black Friday 2017: Where to find the best dea...
B&H Photo has 27″ and 21″ iMacs on sale for up to $200 off MSRP as part of the Black Friday and Holiday sale. Shipping is free, and B&H charges sales tax for NY & NJ residents only: – 27... Read more
Black Friday 2017: Where to find the best dea...
B&H Photo has Mac minis on sale for $100 off MSRP as part of their Black Friday sale, each including free shipping plus NY & NJ sales tax only: – 1.4GHz Mac mini: $399 $100 off MSRP – 2.6GHz... Read more
Black Friday 2017: Find the best deals and lo...
Scan our exclusive price trackers for the latest Black Friday 2017 sales & deals and the lowest prices available on Apple Macs, iPads, and gear from Apple’s authorized resellers. We update the... Read more
Black Friday: 27″ 3.4GHz iMac for $1599, save...
Amazon has the 27″ 3.4GHz Apple iMac on sale for $1599.99 as part of their Black Friday sale. That’s $200 off MSRP, and shipping is free. Their price is currently the lowest price available for this... Read more

Jobs Board

Information Systems Engineer, *Apple* Retai...
# Information Systems Engineer, Apple Retail Engineering Job Number: 112895982 Santa Clara Valley, California, United States Posted: 02-Oct-2017 Weekly Hours: 40.00 Read more
Commerce Engineer, *Apple* Media Products (...
# Commerce Engineer, Apple Media Products (New York City) Job Number: 113028813 New York City, New York, United States Posted: 20-Sep-2017 Weekly Hours: 40.00 **Job Read more
Business Development Manager, *Apple* Pay -...
# Business Development Manager, Apple Pay Job Number: 112919084 Santa Clara Valley, California, United States Posted: 18-Aug-2017 Weekly Hours: 40.00 **Job Summary** Read more
Digital Marketing Media Planner, *Apple* Se...
# Digital Marketing Media Planner, Apple Services Job Number: 113080212 Culver City, California, United States Posted: 03-Oct-2017 Weekly Hours: **Job Summary** 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
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.