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Carbon (API)
Encyclopedia
Carbon is one of Apple Inc.'s procedural application programming interface
s (APIs) for the Macintosh operating system
. It provides C programming language access to Macintosh system services. Carbon provides a good degree of backward compatibility for program
s to run on the now-obsolete Mac OS 8
and 9
, however these systems are no longer actively supported since Apple released the final OS 9 update in December 2001.
Carbon consists of a broad set of functions for managing files, memory, data, the user interface, and other system services. It is implemented as any other API: in Mac OS X, it is spread over several frameworks (each a structure built around a shared library), principally
As an umbrella term
encompassing all C-language API procedures accessing Mac-specific functionality, Carbon is not designed as a discrete system. Rather, it opens nearly all the functionality of Mac OS X to developers who do not know the Objective-C
language required for the broadly-equivalent Cocoa API
.
Carbon is compatible with all of the several executable formats available for PowerPC Mac OS. Binary compatibility between Mac OS X and previous versions requires use of a Preferred Executable Format
file, which Apple never supported in their Xcode
IDE
.
and global variable
s within the operating system. These practices make programs more compact for primitive computers with scarce memory, but hinder the addition of features to the operating system. Carbon adds (and requires) more modern methods for manipulating this information, namely by calling accessor subroutine
s on opaque data type
s. The process of changing a program's syntax to use these functions is termed Carbonization. This makes the application file incompatible with operating systems prior to Mac OS 8.1 at least, although source compatibility is often possible using C preprocessor
macros.
Other changes from the pre-existing API removed features which were conceptually incompatible with Mac OS X, or simply obsolete. For example, applications could no longer install interrupt handler
s or device driver
s.
Carbon was introduced in incomplete form in 2000, as a shared library backward-compatible with 1997's Mac OS 8.1. However, several versions passed before it was mature enough for general use, and late versions require Mac OS 8.6. It is generally necessary to establish the minimum CarbonLib and Mac OS versions when releasing a backward-compatible Carbon application. Versions of CarbonLib are not tied to particular versions of the operating system.
and Objective-C
. In particular, Objective-C is ubiquitous in the human interface systems. With Mac OS X v10.5
, after a transition where new elements of the Carbon interface specifically referred to the underlying Cocoa system, Apple identified Objective-C and Cocoa as the preferred interface to human interface services. Carbon access to various human interface services in the 64-bit operating environment is not available, and significant new features will not be added to the 32-bit Carbon interface. Most other parts of the system, which have less emphasis on Objective-C, are not so affected.
Macintosh applications beginning with Mac OS X v10.5
, released 26 October 2007, has brought the first major limitations to Carbon. Apple does not provide compatibility between the Macintosh graphical user interface
and the C programming language in the 64-bit environment, instead requiring the use of the Objective-C
dialect with the Cocoa API. Although Objective-C can provide significant advantages for code already written to take advantage of its object-oriented philosophy, the need to rewrite large amounts of legacy code has slowed the transition of Carbon-based applications, famously with Adobe Photoshop
, which was eventually updated to Cocoa in April 2010.
This difficulty also extended to Apple's own flagship software packages, as iTunes
and Final Cut Pro
(as well as the features in the QuickTime
engine which powers it) remained written in Carbon for many years.
Incidentally, although Final Cut Pro X has been fully rewritten as a 64-bit Cocoa application, it is missing a significant number of features found in the discontinued Carbon version. iTunes 10.4 was also rewritten as a 64-bit Cocoa application which was released on July 20th, 2011.
, and as such, is composed of "Managers". Each Manager is a functionally-related API, defining sets of data structures and functions to manipulate them. Managers are often interdependent or layered.
Newer parts of Carbon tend to be much more object-oriented in their conception, most of them based on Core Foundation
. Some Managers, such as the HIView Manager (a superset of the Control Manager), are implemented in C++
, but Carbon remains a C
API.
Some examples of Carbon Managers:
model for application design. The application's main event loop
asks the Event Manager for an event using GetNextEvent. If there is an event in the queue, the Event Manager passes it back to the application, where it is handled, otherwise it returns immediately. This behavior is called "busy-waiting
", running the event loop unnecessarily. Busy-waiting reduces the amount of CPU time available for other applications and decreases battery power on laptops. The classic Event Manager dates from the original Mac OS in 1984, when whatever application was running was guaranteed to be the only application running, and where power management was not a concern.
With the advent of MultiFinder and the ability to run more than one application simultaneously came a new Event Manager call, WaitNextEvent, which allows an application to specify a sleep interval. One easy trick for legacy code to adopt a more efficient model without major changes to its source code is simply to set the sleep parameter passed to WaitNextEvent to a very large value—on OS X, this puts the thread to sleep whenever there is nothing to do, and only returns an event when there is one to process. In this way, the polling model is quickly inverted to become equivalent to the callback model, with the application performing its own event dispatching in the original manner. There are loopholes, though. For one, the legacy toolbox call ModalDialog, for example, calls the older GetNextEvent function internally, resulting in polling in a tight loop without blocking.
Carbon introduces a replacement system, called the Carbon Event Manager. (The original Event Manager still exists for compatibility with legacy applications). Carbon Event Manager provides the event loop for the developer (based on Core Foundation's
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
s (APIs) for the Macintosh operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
. It provides C programming language access to Macintosh system services. Carbon provides a good degree of backward compatibility for program
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
s to run on the now-obsolete Mac OS 8
Mac OS 8
Mac OS 8 is an operating system that was released by Apple Computer on July 26, 1997. It represented the largest overhaul of the Mac OS since the release of System 7, some six years previously. It puts more emphasis on color than previous operating systems...
and 9
Mac OS 9
Mac OS 9 is the final major release of Apple's Mac OS before the launch of Mac OS X. Introduced on October 23, 1999, Apple positioned it as "The Best Internet Operating System Ever," highlighting Sherlock 2's Internet search capabilities, integration with Apple's free online services known as...
, however these systems are no longer actively supported since Apple released the final OS 9 update in December 2001.
Overview
Carbon.framework, ApplicationServices.framework, and CoreServices.framework, and in older Mac OS, it resides in a single shared library named CarbonLib.As an umbrella term
Umbrella term
An umbrella term is a word that provides a superset or grouping of concepts that all fall under a single common category. Umbrella term is also called a hypernym. For example, cryptology is an umbrella term that encompasses cryptography and cryptanalysis, among other fields...
encompassing all C-language API procedures accessing Mac-specific functionality, Carbon is not designed as a discrete system. Rather, it opens nearly all the functionality of Mac OS X to developers who do not know the Objective-C
Objective-C
Objective-C is a reflective, object-oriented programming language that adds Smalltalk-style messaging to the C programming language.Today, it is used primarily on Apple's Mac OS X and iOS: two environments derived from the OpenStep standard, though not compliant with it...
language required for the broadly-equivalent Cocoa API
Cocoa (API)
Cocoa is Apple's native object-oriented application programming interface for the Mac OS X operating system and—along with the Cocoa Touch extension for gesture recognition and animation—for applications for the iOS operating system, used on Apple devices such as the iPhone, the iPod Touch, and...
.
Carbon is compatible with all of the several executable formats available for PowerPC Mac OS. Binary compatibility between Mac OS X and previous versions requires use of a Preferred Executable Format
Preferred Executable Format
The Preferred Executable Format is a file format that specifies the format of executable files and other object code. PEF executables are also called Code Fragment Manager files ....
file, which Apple never supported in their Xcode
Xcode
Xcode is a suite of tools, developed by Apple, for developing software for Mac OS X and iOS. Xcode 4.2, the latest major version, is available on the Mac App Store for free for Mac OS X 10.7 , and on the Apple Developer Connection website for free to registered developers Xcode is a suite of tools,...
IDE
Integrated development environment
An integrated development environment is a software application that provides comprehensive facilities to computer programmers for software development...
.
Evolution and backward compatibility
Carbon was designed as a cleaner implementation of the preceding Macintosh API. As originally designed, Macintosh applications access data recordsRecord (computer science)
In computer science, a record is an instance of a product of primitive data types called a tuple. In C it is the compound data in a struct. Records are among the simplest data structures. A record is a value that contains other values, typically in fixed number and sequence and typically indexed...
and global variable
Global variable
In computer programming, a global variable is a variable that is accessible in every scope . Interaction mechanisms with global variables are called global environment mechanisms...
s within the operating system. These practices make programs more compact for primitive computers with scarce memory, but hinder the addition of features to the operating system. Carbon adds (and requires) more modern methods for manipulating this information, namely by calling accessor subroutine
Subroutine
In computer science, a subroutine is a portion of code within a larger program that performs a specific task and is relatively independent of the remaining code....
s on opaque data type
Opaque data type
In computer science, an opaque data type is a user defined data type used like built-in data type. It is incompletely defined in an interface, so that ordinary client programs can only manipulate data of that type by calling procedures that have access to the missing information.-Overview:Opaque...
s. The process of changing a program's syntax to use these functions is termed Carbonization. This makes the application file incompatible with operating systems prior to Mac OS 8.1 at least, although source compatibility is often possible using C preprocessor
C preprocessor
The C preprocessor is the preprocessor for the C and C++ computer programming languages. The preprocessor handles directives for source file inclusion , macro definitions , and conditional inclusion ....
macros.
Other changes from the pre-existing API removed features which were conceptually incompatible with Mac OS X, or simply obsolete. For example, applications could no longer install interrupt handler
Interrupt handler
An interrupt handler, also known as an interrupt service routine , is a callback subroutine in microcontroller firmware, operating system or device driver whose execution is triggered by the reception of an interrupt...
s or device driver
Device driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
s.
Carbon was introduced in incomplete form in 2000, as a shared library backward-compatible with 1997's Mac OS 8.1. However, several versions passed before it was mature enough for general use, and late versions require Mac OS 8.6. It is generally necessary to establish the minimum CarbonLib and Mac OS versions when releasing a backward-compatible Carbon application. Versions of CarbonLib are not tied to particular versions of the operating system.
Today
The development of Mac OS X APIs reflect that of the underlying operating system. Mac OS X is written mostly in CC (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
and Objective-C
Objective-C
Objective-C is a reflective, object-oriented programming language that adds Smalltalk-style messaging to the C programming language.Today, it is used primarily on Apple's Mac OS X and iOS: two environments derived from the OpenStep standard, though not compliant with it...
. In particular, Objective-C is ubiquitous in the human interface systems. With Mac OS X v10.5
Mac OS X v10.5
Mac OS X Leopard is the sixth major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers. Leopard was released on 26 October 2007 as the successor of Tiger , and is available in two variants: a desktop version suitable for personal computers, and a...
, after a transition where new elements of the Carbon interface specifically referred to the underlying Cocoa system, Apple identified Objective-C and Cocoa as the preferred interface to human interface services. Carbon access to various human interface services in the 64-bit operating environment is not available, and significant new features will not be added to the 32-bit Carbon interface. Most other parts of the system, which have less emphasis on Objective-C, are not so affected.
Transition to Cocoa
The transition to 64-bit64-bit
64-bit is a word size that defines certain classes of computer architecture, buses, memory and CPUs, and by extension the software that runs on them. 64-bit CPUs have existed in supercomputers since the 1970s and in RISC-based workstations and servers since the early 1990s...
Macintosh applications beginning with Mac OS X v10.5
Mac OS X v10.5
Mac OS X Leopard is the sixth major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers. Leopard was released on 26 October 2007 as the successor of Tiger , and is available in two variants: a desktop version suitable for personal computers, and a...
, released 26 October 2007, has brought the first major limitations to Carbon. Apple does not provide compatibility between the Macintosh graphical user interface
Graphical user interface
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
and the C programming language in the 64-bit environment, instead requiring the use of the Objective-C
Objective-C
Objective-C is a reflective, object-oriented programming language that adds Smalltalk-style messaging to the C programming language.Today, it is used primarily on Apple's Mac OS X and iOS: two environments derived from the OpenStep standard, though not compliant with it...
dialect with the Cocoa API. Although Objective-C can provide significant advantages for code already written to take advantage of its object-oriented philosophy, the need to rewrite large amounts of legacy code has slowed the transition of Carbon-based applications, famously with Adobe Photoshop
Adobe Photoshop
Adobe Photoshop is a graphics editing program developed and published by Adobe Systems Incorporated.Adobe's 2003 "Creative Suite" rebranding led to Adobe Photoshop 8's renaming to Adobe Photoshop CS. Thus, Adobe Photoshop CS5 is the 12th major release of Adobe Photoshop...
, which was eventually updated to Cocoa in April 2010.
This difficulty also extended to Apple's own flagship software packages, as iTunes
ITunes
iTunes is a media player computer program, used for playing, downloading, and organizing digital music and video files on desktop computers. It can also manage contents on iPod, iPhone, iPod Touch and iPad....
and Final Cut Pro
Final Cut Pro
Final Cut Pro is a non-linear video editing software developed by Macromedia Inc. and then Apple Inc. The most recent version, Final Cut Pro X, runs on Mac personal computers powered by Mac OS X version 10.6.7 or later and using Intel processors...
(as well as the features in the QuickTime
QuickTime
QuickTime is an extensible proprietary multimedia framework developed by Apple Inc., capable of handling various formats of digital video, picture, sound, panoramic images, and interactivity. The classic version of QuickTime is available for Windows XP and later, as well as Mac OS X Leopard and...
engine which powers it) remained written in Carbon for many years.
Incidentally, although Final Cut Pro X has been fully rewritten as a 64-bit Cocoa application, it is missing a significant number of features found in the discontinued Carbon version. iTunes 10.4 was also rewritten as a 64-bit Cocoa application which was released on July 20th, 2011.
Architecture
Carbon descends from the ToolboxMacintosh Toolbox
The Macintosh Toolbox is a set of application programming interfaces with a particular access mechanism. They implement many of the high-level features of the Mac OS. The Toolbox consists of a number of "managers," software components such as QuickDraw, responsible for drawing onscreen graphics,...
, and as such, is composed of "Managers". Each Manager is a functionally-related API, defining sets of data structures and functions to manipulate them. Managers are often interdependent or layered.
Newer parts of Carbon tend to be much more object-oriented in their conception, most of them based on Core Foundation
Core Foundation
Core Foundation is a C application programming interface in Mac OS X & iOS, and is a mix of low-level routines and wrapper functions...
. Some Managers, such as the HIView Manager (a superset of the Control Manager), are implemented in C++
C++
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
, but Carbon remains a C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
API.
Some examples of Carbon Managers:
- File Manager — manages access to the file system, opening closing, reading and writing files.
- Resource Manager — manages access to resources, which are predefined chunks of data a program may require. Calls File Manager to read and write resources from disk files. Examples of resources include icons, sounds, images, templates for widgets, etc.
- Font Manager — manages fontTypefaceIn typography, a typeface is the artistic representation or interpretation of characters; it is the way the type looks. Each type is designed and there are thousands of different typefaces in existence, with new ones being developed constantly....
s. Deprecated (as part of QuickDrawQuickDrawQuickDraw is the 2D graphics library and associated Application Programming Interface which is a core part of the classic Apple Macintosh operating system. It was initially written by Bill Atkinson and Andy Hertzfeld. QuickDraw still exists as part of the libraries of Mac OS X, but has been...
) since Mac OS X v10.4Mac OS X v10.4Mac OS X v10.4 Tiger is the fifth major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers. Tiger was released to the public on 29 April 2005 for US$129.95 as the successor to Mac OS X Panther , which had been released 18 months earlier...
, in favor of Apple Type Services (ATS). - QuickDrawQuickDrawQuickDraw is the 2D graphics library and associated Application Programming Interface which is a core part of the classic Apple Macintosh operating system. It was initially written by Bill Atkinson and Andy Hertzfeld. QuickDraw still exists as part of the libraries of Mac OS X, but has been...
— 2D graphics primitives. Deprecated since Mac OS X v10.4Mac OS X v10.4Mac OS X v10.4 Tiger is the fifth major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers. Tiger was released to the public on 29 April 2005 for US$129.95 as the successor to Mac OS X Panther , which had been released 18 months earlier...
, in favor of Quartz 2D. - Carbon Event Manager — converts user and system activity into events that code can recognise and respond to.
- HIObject — a completely new object-oriented API which brings to Carbon an OOObject-oriented programmingObject-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...
model for building GUIs. This is available in Mac OS X v10.2Mac OS X v10.2Mac OS X version 10.2 "Jaguar" is the third major release of Mac OS X, Apple's desktop and server operating system. It superseded Mac OS X v10.1 code name Puma and preceded Mac OS X Panther...
or later, and gives Carbon programmers some of the tools that Cocoa developers have long been familiar with. Starting with Mac OS X v10.2Mac OS X v10.2Mac OS X version 10.2 "Jaguar" is the third major release of Mac OS X, Apple's desktop and server operating system. It superseded Mac OS X v10.1 code name Puma and preceded Mac OS X Panther...
, HIObject is the base class for all GUI elements in Carbon. HIView is supported by Interface BuilderInterface BuilderInterface Builder is a software development application for Apple's Mac OS X operating system. It is part of Xcode , the Apple Developer Connection developer's toolset. Interface Builder allows Cocoa and Carbon developers to create interfaces for applications using a graphical user...
, part of Apple's developer tools. Traditionally GUI architectures of this sort have been left to third-party application frameworks to provide. Starting with Mac OS X v10.4, HIObjects are NSObjects and inherit the ability to be serialized into data streams for transport or saving to disk. - HITheme — uses QuickDraw and Quartz to render graphical user interfaceGraphical user interfaceIn computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
(GUI) elements to the screen. HITheme was introduced in Mac OS X v10.3Mac OS X v10.3Mac OS X Panther is the fourth major release of Mac OS X, Apple’s desktop and server operating system. It followed Mac OS X v10.2 "Jaguar" and preceded Mac OS X Tiger...
, and Appearance Manager is a compatibility layer on top of HITheme since that version. - HIView Manager — manages creation, drawing, hit-testingHit-testingIn computer graphics programming, hit-testing is the process of determining whether a user-controlled cursor intersects a given shape, line, or curve drawn on the screen...
, and manipulation of controls. Since Mac OS X v10.2, all controls are HIViews. In Mac OS X v10.4, the Control Manager was renamed HIView Manager. - Window Manager — manages creation, positioning, updating, and manipulation of windows. Since Mac OS X v10.2, windows have a root HIView.
- Menu Manager — manages creation, selection, and manipulation of menus. Since Mac OS X v10.2, menus are HIObjects. Since Mac OS X v10.3, menu content may be drawn using HIViews, and all standard menus use HIViews to draw.
Event handling
The Mac Toolbox's Event Manager originally used a pollingPolling (computer science)
Polling, or polled operation, in computer science, refers to actively sampling the status of an external device by a client program as a synchronous activity. Polling is most often used in terms of input/output , and is also referred to as polled or software driven .Polling is sometimes used...
model for application design. The application's main event loop
Event loop
In computer science, the event loop, message dispatcher, message loop, message pump, or run loop is a programming construct that waits for and dispatches events or messages in a program...
asks the Event Manager for an event using GetNextEvent. If there is an event in the queue, the Event Manager passes it back to the application, where it is handled, otherwise it returns immediately. This behavior is called "busy-waiting
Busy waiting
In software engineering, busy-waiting or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as whether keyboard input is available, or if a lock is available. Spinning can also be used to generate an arbitrary time delay, a technique that was necessary...
", running the event loop unnecessarily. Busy-waiting reduces the amount of CPU time available for other applications and decreases battery power on laptops. The classic Event Manager dates from the original Mac OS in 1984, when whatever application was running was guaranteed to be the only application running, and where power management was not a concern.
With the advent of MultiFinder and the ability to run more than one application simultaneously came a new Event Manager call, WaitNextEvent, which allows an application to specify a sleep interval. One easy trick for legacy code to adopt a more efficient model without major changes to its source code is simply to set the sleep parameter passed to WaitNextEvent to a very large value—on OS X, this puts the thread to sleep whenever there is nothing to do, and only returns an event when there is one to process. In this way, the polling model is quickly inverted to become equivalent to the callback model, with the application performing its own event dispatching in the original manner. There are loopholes, though. For one, the legacy toolbox call ModalDialog, for example, calls the older GetNextEvent function internally, resulting in polling in a tight loop without blocking.
Carbon introduces a replacement system, called the Carbon Event Manager. (The original Event Manager still exists for compatibility with legacy applications). Carbon Event Manager provides the event loop for the developer (based on Core Foundation's
CFRunLoop in the current implementation); the developer sets up event handlers and enters the event loop in the main function, and waits for Carbon Event Manager to dispatch events to the application.