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

TextSoap 8.3.3 - Automate tedious text d...
TextSoap can automatically remove unwanted characters, fix up messed up carriage returns, and do pretty much anything else that we can think of to text. Save time and effort. Be more productive. Stop... Read more
Apple iTunes 12.6 - Play Apple Music and...
Apple iTunes lets you organize and stream Apple Music, download and watch video and listen to Podcasts. It can automatically download new music, app, and book purchases across all your devices and... Read more
Airmail 3.2.4 - Powerful, minimal email...
Airmail is an mail client with fast performance and intuitive interaction. Support for iCloud, MS Exchange, Gmail, Google Apps, IMAP, POP3, Yahoo!, AOL, Outlook.com, Live.com. Airmail was designed... Read more
MacPilot 9.0.6 - Enable over 1,200 hidde...
MacPilot gives you the power of UNIX and the simplicity of Macintosh, which means a phenomenal amount of untapped power in your hands! Use MacPilot to unlock over 1,200 features, and access them all... Read more
Jamf Pro 9.98 - Powerful sysadmin/enterp...
Jamf Pro (formerly Casper Suite) is the EMM tool that delights IT pros and the users they support by delivering on the promise of unified endpoint management for Apple devices. At Jamf, connecting... Read more
PopChar 7.7 - $16.99 (51% off)
PopChar helps you get the most out of your font collection. With its crystal-clear interface, PopChar provides a frustration-free way to access any font's special characters. Features Expanded... Read more
RapidWeaver 7.3.1 - Create template-base...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
Sparkle Pro 2.1.4 - $79.99
Sparkle Pro will change your mind if you thought building websites wasn't for you. Sparkle is the intuitive site builder that lets you create sites for your online portfolio, team or band pages, or... Read more
Affinity Designer 1.5.5 - Vector graphic...
Affinity Designer is an incredibly accurate vector illustrator that feels fast and at home in the hands of creative professionals. It intuitively combines rock solid and crisp vector art with... Read more
djay Pro 1.4.3 - Transform your Mac into...
djay Pro provides a complete toolkit for performing DJs. Its unique modern interface is built around a sophisticated integration with iTunes and Spotify, giving you instant access to millions of... Read more

Failbetter Games details changes coming...
Sunless Sea, Failbetter Games' dark and gloomy sea explorer, sets sail for the iPad tomorrow. Ahead of the game's launch, Failbetter took to Twitter to discuss what will be different in the mobile version of the game. Many of the changes make... | Read more »
Splish, splash! The Pokémon GO Water Fes...
Niantic is back with a new festival for dedicated Pokémon GO collectors. The Water Festival officially kicks off today at 1 P.M. PDT and runs through March 29. Magikarp, Squirtle, Totodile, and their assorted evolved forms will be appearing at... | Read more »
Death Road to Canada (Games)
Death Road to Canada 1.0 Device: iOS Universal Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: Get it now at the low launch price! Price will go up a dollar every major update. Update news at the bottom of this... | Read more »
Bean's Quest Beginner's Guide:...
Bean's Quest is a new take on both the classic platformer and the endless runner, and it's free on the App Store for the time being. Instead of running constantly, you can't stop jumping. That adds a surprising new level of challenge to the game... | Read more »
How to rake in the cash in Bit City
Our last Bit City guide covered the basics. Now it's time to get into some of the more advanced techniques. In the later cities, cash flow becomes much more difficult, so you'll want to develop some strategies if you want to complete each level.... | Read more »
PixelTerra (Games)
PixelTerra 1.1.1 Device: iOS Universal Category: Games Price: $.99, Version: 1.1.1 (iTunes) Description: The world of PixelTerra is quite dangerous so you need to build a shelter, find some food supply and get ready to protect... | Read more »
Tokaido™ (Games)
Tokaido™ 1.0 Device: iOS Universal Category: Games Price: $6.99, Version: 1.0 (iTunes) Description: Discover the digital adaptation of Tokaido, the boardgame phenomenon that has already sold more than 250,000 copies worldwide, and... | Read more »
Card Thief (Games)
Card Thief 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Card Thief is a solitaire style stealth game played with a deck of cards. In Card Thief you move through a deck of cards as a... | Read more »
Smilegate’s crafting battler Super Tank...
Super Tank Rumbleputs you in the seat of your very own, handcrafted tank. You can choose from over 100 different parts to create your Super Tank before taking it out to wreak havoc on your opponents in glorious PVP combat. Now, Smilegate is upping... | Read more »
The best games to play while you wait fo...
Mass Effect: Andromeda arrives this coming Tuesday and people are getting understandably antsy. There's a whole weekend standing between us and a brand new Bioware adventure. What's a geek to do? Well, you could certainly give these fine mobile... | Read more »

Price Scanner via MacPrices.net

13-inch Touch Bar MacBook Pros on sale for up...
B&H Photo has the Apple 13″ Touch Bar MacBook Pros in stock today and on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.9GHz/512GB Touch Bar... Read more
Today only! 15-inch 2.7GHz Space Gray Touch B...
B&H Photo has the new 2016 15″ 2.7GHz Space Gray Apple Touch Bar MacBook Pro in stock today and on sale for $300 off MSRP for today only. Shipping is free, and B&H charges NY sales tax only... Read more
New $329 iPad A Fabulous Value; 10.5-Inch iPa...
Part of the iPad upgrade/new model puzzle is now in place. Yesterday, as KGI Securities financial services group analyst Ming-Chi Kuo last summer predicted they would, Apple released a new low-cost 9... Read more
New 9.7-Inch iPad Features All Of The Fun...
Apple today updated its most popular-sized iPad, featuring a brighter 9.7-inch Retina display and best-in-class performance at its most affordable price ever, starting at $329 (US) with 32GB of... Read more
Apple Introduces iPhone 7 and iPhone 7 Plus (...
Apple today announced iPhone 7 and iPhone 7 Plus (PRODUCT)RED Special Edition in a vibrant red matte aluminum finish, in recognition of more than 10 years of partnership between Apple and (RED). This... Read more
Apple now offering Certified Refurbished 15-i...
Apple is now offering Certified Refurbished 2016 15″ Touch Bar MacBook Pros for $360-$420 off original MSRP. An Apple one-year warranty is included with each model, and shipping is free: - 15″ 2.6GHz... Read more
Apple Introduces Clips: A Free Innovative Way...
Apple today introduced Clips, a new app that makes it quick and fun for anyone to create expressive videos on iPhone and iPad. The app features a unique design for combining video clips, photos and... Read more
Urban Armor Gear Unveils Case For 4th Generat...
Orange County, California based Urban Armor Gear (UAG), designers of rugged, lightweight protective cases for phones, tablets and laptops, has released its latest drop-tested cases for Apple’s 4th... Read more
Most Users Continue To Prefer 5.0 to 5.3 Inch...
In the first half of 2016, US and UK smartphone users were most likely to be interested in purchasing a device with a 5.3″ or 5.0″ display. Findings in a new report from the User Experience... Read more
12-inch 1.2GHz Retina MacBooks on sale for up...
B&H has 12″ 1.2GHz Retina MacBooks on sale for up to $200 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 12″ 1.2GHz Space Gray Retina MacBook: $1439.99 $160 off MSRP - 12″ 1... Read more

Jobs Board

*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
Fulltime aan de slag als shopmanager in een h...
Ben jij helemaal gek van Apple -producten en vind je het helemaal super om fulltime shopmanager te zijn in een jonge en hippe elektronicazaak? Wil jij werken in Read more
Starte Dein Karriere-Abenteuer in den Hauptst...
…mehrsprachigen Teams betreust Du Kunden von bekannten globale Marken wie Apple , Mercedes, Facebook, Expedia, und vielen anderen! Funktion Du wolltest schon Read more
Starte Dein Karriere-Abenteuer in den Hauptst...
…mehrsprachigen Teams betreust Du Kunden von bekannten globale Marken wie Apple , Mercedes, Facebook, Expedia, und vielen anderen! Funktion Du wolltest schon 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.