TweetFollow Us on Twitter

Jan 01 Online Volume Number: 17 (2001)
Issue Number: 1
Column Tag: MacTech Online

MacTech Online

by Jeff Clites <online@mactech.com>

In our previous column we began coverage of a set of technologies that I'm calling the "New Basics," in recognition that "the things that every programmer should know" are changing, and as they change we're converging on a set which is the same for all programmers-there are no longer different sets for different platforms. This is in part because the fundamental, low-level differences between operating systems are shrinking, and in part because the focus is shifting toward technologies which are new to all platforms, and which are being embraced by all platforms as they emerge. We also noted that this is leading to a sort of impromptu cooperation, and companies like IBM which used to be archetypal bad guy are now great sources of information for Macintosh programmers who are new to the Unix side of computing. Our first New Basic was XML, which is the most-hyped technology of the day, and is likely to dominate information interchange for some time to come. This month we are going to take a look at threading-both how it will be conceptually different under Mac OS X than under Mac OS 9, and how it will be more important there as well.

Preemptive Threading

Most Macintosh developers will be accustomed to a "cooperative" environment, where an application has exclusive use of the processor (and other system resources) until it explicitly yields control to other waiting processes. Threading under Mac OS 9 is also typically cooperatively scheduled, so that threads within a single application have to explicitly yield for other threads to proceed. This type of scheduling simplifies certain issues surrounding concurrent access to memory and system resources, but it can be difficult for a developer to know how often, and when, to yield the processor in order to provide the best overall system performance. Also, the majority of the Toolbox is not thread safe, so that you have to be very careful about the types of operations you perform outside of the main thread. As a result, under Mac OS 9 applications tend to be single-threaded if at all possible.

Under Mac OS X, as under other Unix-based operating systems, both processes and threads are scheduled preemptively, so that the kernel makes all scheduling decisions and a thread or process can be interrupted at any time. From the point of view of a programmer, this means that you can never be sure that two operations within your application will take place without another process interrupting. The benefit of this approach is that you never has to explicitly code time-consuming sections of your application to yield the processor in order to prevent freezing the user's system for long periods, and you can perform blocking I/O operations in a thread and know that other threads and processes will happily proceed while yours is waiting for data to be read transferred. This simplifies many uses of threads, but introduces complications of its own: you have to guard critical sections of code and data from concurrent access if they are going to be used by multiple threads (even reading data from a variable cannot be assumed to be an atomic operation), and you can't assume that the state of the system has not changed from one line of code to the next (for instance, it isn't reliable to check for the existence of a file and then try to open it as a separate step, because the file could be deleted in between the two operations, even if they occur back-to-back within your program). Preemptive scheduling requires a certain paranoia on the part of the programmer, but it leads to an overall more responsive and reliable system, and it allows simple applications to be written simply, without worrying that they might accidentally hijack the processor. And of course, threading makes it possible for a single application to take advantage of multiple processors on systems which have them, and in fact on such systems two threads within a single application can be executing at literally the same time.

POSIX Threads

The fundamental threading library under Mac OS X is POSIX Threads, or Pthreads for short. This will be new to veteran OpenStep programmers as well as to classic Macintosh programmers, as Mac OS X Server and previous NeXT-derived operating systems used a different threading library, called Cthreads. The big benefit of Pthreads is that applications using them should be portable to other POSIX-compliant operating systems (if the rest of the code is portable, of course), and this will make it that much easier to bring standard Unix tools and applications over to the Macintosh. For most applications it won't be necessary to use the Pthreads library directly, as Cocoa has its own threading facilities which provide a higher-level view and insulate the programmer from the details of the underlying threading library. Even so, the conceptual model remains the same, and Macintosh programmers which are new to preemptive threading will benefit from the wealth of information there is available on POSIX threading. Also, if you plan to develop (or port) more traditional Unix-style applications you will need to know about the lower-level libraries in more detail.

A good starting point is the article How to program with threads on SunWorld Online, which talks about programming with threads in general, and the advantages that they offer. Next, IBM's developerWorks site has a series of articles which cover POSIX threads specifically. Like many of their articles, these are written with a Linux audience in mind, but most of the information is nevertheless relevant, as POSIX is explicitly cross platform. These articles will give you a good feel for the issues involved, and point out the potential complexities of using threads.

After you've gotten a handle on the major concepts, you'll want to find more in-depth coverage of the details of using Pthreads. There are several online tutorials which can help. In particular, Getting Started With POSIX Threads is a brief tutorial which will help solidify some key points, and then you can move on to more comprehensive coverage in Multi-Threaded Programming With POSIX Threads and POSIX Threads Programming, both of which are quite thorough.

If you are curious about other issues surrounding threading, you should check the comp.programming.threads FAQ. Also, if you are interested in the different possible strategies for actually implement a threading library, the Navy has an article which covers the strengths and weaknesses of three different approaches. Finally, you may want to visit the Programming POSIX Threads web site, which has pointers to further information.

There are several books about Pthreads, and I always find it helpful to have a detailed printed reference to augment all of the web-based information. Programming with POSIX Threads by David R. Butenhof (ISBN: 0-201-63392-2) is my favorite and is often recommended by others, but there are several alternatives available, including Pthreads Programming (ISBN: 1-56592-115-1) and Multithreaded Programming With Pthreads (ISBN: 0136807291). Take a look and see which one suites you the best.

Now you should be up to speed on basic number two. Keep your eye on this column in coming months, because we're not done with the New Basics yet!

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Monolingual 1.6.4 - Remove unwanted OS X...
Monolingual is a program for removing unnecesary language resources from OS X, in order to reclaim several hundred megabytes of disk space. If you use your computer in only one (human) language, you... Read more
CleanApp 5.0 - Application deinstaller a...
CleanApp is an application deinstaller and archiver.... Your hard drive gets fuller day by day, but do you know why? CleanApp 5 provides you with insights how to reclaim disk space. There are... Read more
Fantastical 2.0 - Create calendar events...
Fantastical is the Mac calendar you'll actually enjoy using. Creating an event with Fantastical is quick, easy, and fun: Open Fantastical with a single click or keystroke Type in your event details... Read more
Cocktail 8.2 - General maintenance and o...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
Direct Mail 4.0.4 - Create and send grea...
Direct Mail is an easy-to-use, fully-featured email marketing app purpose-built for OS X. It lets you create and send great looking email campaigns. Start your newsletter by selecting from a gallery... Read more
jAlbum Pro 12.6 - Organize your digital...
jAlbum Pro has all the features you love in jAlbum, but comes with a commercial license. With jAlbum, you can create gorgeous custom photo galleries for the Web without writing a line of code!... Read more
jAlbum 12.6 - Create custom photo galler...
With jAlbum, you can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly, with pro results Simply drag and drop photos into groups, choose a design... Read more
Lyn 1.5.9 - Lightweight image browser an...
Lyn is a lightweight and fast image browser and viewer designed for photographers, graphic artists and Web designers. Featuring an extremely versatile and aesthetically pleasing interface, it... Read more
Sublime Text 3080 - Sophisticated text e...
Sublime Text is a sophisticated text editor for code, markup, and prose. You'll love the slick user interface, extraordinary features, and amazing performance. Goto Anything. Use Goto Anything to... Read more
WALTR 1.0.11 - Drag-and-drop any media f...
WALTR is designed to make it easy to upload and convert any music or video file to an iPad or iPhone format for native playback. It supports a huge variety of media file types, including MP3, MP4,... Read more

Bio Inc's New Expansion is Infectin...
Bio Inc., by DryGin Studios, is the real time strategy game where you infect a human body with the worst virus your evil brain can design. Recently, the game was updated to add a whole lot of new features. Now you can play the new “Lethal”... | Read more »
The Monocular Minion is Here! Despicable...
Despicable Me: Minion Rush, by Gameloft, is introducing a new runner to the mix in their latest update. Now you can play as Carl, the prankster minion. Carl has a few new abilities to play with, including running at a higher speed from the start.... | Read more »
Dungeon of Madness (Games)
Dungeon of Madness 1.0.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0.0 (iTunes) Description: Dungeon of Madness is an action game where you rotate tiles to create our own route. Help the hero by connecting the... | Read more »
Filters for iPhone (Photography)
Filters for iPhone 1.0 Device: iOS iPhone Category: Photography Price: $.99, Version: 1.0 (iTunes) Description: | Read more »
Jump'N'Shoot Attack (Games)
Jump'N'Shoot Attack 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: A mobile game for gamers! Join Louise Lightfoot, the legendary "Master of Jumping and Shooting", on her mission to save... | Read more »
Space Bounties Inc. (Games)
Space Bounties Inc. 1.4 Device: iOS Universal Category: Games Price: $1.99, Version: 1.4 (iTunes) Description: SuperGameDroid: 4/5 "Satisfying futuristic RPG combat, high replay value, and a heavy dose of nostalgia make Space... | Read more »
Gamebook: Pocket RPG (Games)
Gamebook: Pocket RPG 1.0.11 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.11 (iTunes) Description: Walk into the Land of Lanthir Lamath ruled by wicked skeletons and fight for your life in a thrilling adventure.... | Read more »
Kids Can Mix, Match, and Catch with Tata...
Tatadada MixMatch, by Tatadada Ltd, is a mobile version of the classic game of mix & match. The game uses brightly colored creatures to train your children's pattern matching skills and hand-eye coordination. It's aimed at children around age 5... | Read more »
The Trace: Murder Mystery Game (Games)
The Trace: Murder Mystery Game 1.2.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.2.0 (iTunes) Description: | Read more »
This Week at 148Apps: March 16-20, 2015
Spring Roars In At 148Apps How do you know what apps are worth your time and money? Just look to the review team at 148Apps. We sort through the chaos and find the apps you're looking for. The ones we love become Editor’s Choice, standing out above... | Read more »

Price Scanner via MacPrices.net

Logitech Says MX Master Is Its Most Advanced...
Logitech’s new MX Master Wireless Mouse incorporates the best of Logitech’s many computer mouse innovations into a striking hand-sculpted design. The company claims that the MX Master creates a new... Read more
Save up to $300 on a new Mac, $30 on an iPad,...
Purchase a new Mac or iPad at The Apple Store for Education and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free,... Read more
Apple refurbished 2014 MacBook Airs available...
The Apple Store lowered prices on Apple Certified Refurbished 2014 MacBook Airs recently, with models now available starting at $679. An Apple one-year warranty is included with each MacBook, and... Read more
Mac Notebook Evolution; A Desktop Replacement...
More often than not right from the beginning, Apple’s Macs have tended to skew toward small. The original Macs were called “compacts,”, and notwithstanding a few exceptions like the honking Big Mac... Read more
13-inch 1.4GHz/128GB MacBook Air (Apple refur...
The Apple Store has Apple Certified Refurbished 2014 13″ 1.4GHz/128GB MacBook Airs available for $759 including free shipping plus Apple’s standard one-year warranty. Their price is $240 off original... Read more
YEP! Alternative Browser for iOS Now Supports...
Pfaeffikon, Switzerland based Power App AG has announced the release of an update to their Yep! Web Browser (v1.3.0) for iOS8 iPhone and iPad. Yep! hit the App Store shortly after the release of iOS... Read more
15-inch Retina MacBook Pros on sale for up to...
B&H Photo has the new 2014 15″ Retina MacBook Pros on sale for up to $250 off MSRP for a limited time. Shipping is free, and B&H charges NY sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $... Read more
Clearance 13-inch Retina MacBook Pros availab...
B&H Photo has leftover 2014 13″ Retina MacBook Pros on sale for up to $250 off original MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.6GHz/128GB Retina MacBook Pro: $1098... Read more
Clearance 2014 MacBook Airs on sale for up to...
B&H Photo has MacBook Airs on sale for up to $180 off original MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 128GB MacBook Air: $789.99 110 off original MSRP - 11″ 256GB... Read more
Apple refurbished Time Capsules available for...
The Apple Store has certified refurbished Time Capsules available for $100 off MSRP. Apple’s one-year warranty is included with each Time Capsule, and shipping is free: - 2TB Time Capsule: $199, $100... Read more

Jobs Board

*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - D...
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* Systems Engineer - Pre Sales, Educat...
…is responsible for proactively providing technical expertise to drive sales of Apple solutions into assigned accounts. The SE architects, validates, and assists in Read more
Sr. Technical Services Consultant, *Apple*...
**Job Summary** Apple Professional Services (APS) has an opening for a senior technical position that contributes to Apple 's efforts for strategic and transactional Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.