TweetFollow Us on Twitter

Apr 97 Dialog Box

Volume Number: 13 (1997)
Issue Number: 4
Column Tag: Dialog Box

Dialog Box

Bolo is a PBRead Completion Routine

Dear Editor,

I was pleased to see the article in MacTech December 1996 encouraging programmers to use asynchronous I/O, but unfortunately some of the details in the article were not correct. Richard Clark wrote "The completion routine for PBRead is especially poor, as it receives no parameters... This routine appears to have A5 set up for it..."

Firstly, the PBRead completion routine does get passed a parameter (a pointer to the parameter block that has just completed) and secondly, A5 is not guaranteed to be set up to point at your globals. A5 will be pointing to the globals of whichever application was interrupted to execute the completion routine (which might even be your own application, which is why A5 may sometimes appear to be set up correctly). If your completion routine tries to access your program's globals without first making sure to set up A5 correctly, the Mac will crash.

Fortunately, there's no problem as long as you know how to deal with it: Because the PBRead completion routine gets passed a pointer to the parameter block, you can use this to pass it as many extra parameters as you like.

1. Define a new "extended" PBRead parameter block like this

typedef struct
{
ioParam io;
void *regA5;
short my_parameter;
// ... and, so on, as many as you like
} ex_ioParam;

2. Before you call PBRead, fill in the parameters that you want the completion routine to get (especially the Register A5 value).

static ex_ioParam pb; pb.io.ioCompletion = CompletionRoutine;
pb.io.ioRefNum   = refnum;
// ... and so on
pb.regA5 = GetGlobalsRegister();
PBRead((ParmBlkPtr)&pb,TRUE);

3. In the completion routine, set up the correct A5 value and access other parameters as necessary:

static void CompletionRoutine(void)
{
register ex_ioParam *pb = GetRegisterA0(); register void* oldGlobalsReg 
= SetGlobalsRegister(pb->regA5);
// ... Do your stuff
SetGlobalsRegister(oldGlobalsReg);
}

If you don't already have the 68K register accessor functions defined, they are:

#pragma parameter __D0 GetRegisterD0() // MOVEA.L D0,D0 local void* GetRegisterD0(void) 
= { 0x2000 };

#pragma parameter __A0 GetRegisterA4() // MOVEA.L A4,A0 local void* GetRegisterA4(void) 
= { 0x204C };
#pragma parameter __A0 GetRegisterA5() // MOVEA.L A5,A0 local void* GetRegisterA5(void) 
= { 0x204D };
#pragma parameter __A0 SetRegisterA4(__A0)   // EXG A0,A4 local 
void* SetRegisterA4(void*) = { 0xC14C };
#pragma parameter __A0 SetRegisterA5(__A0)   // EXG A0,A5 local 
void* SetRegisterA5(void*) = { 0xC14D };
#ifdef THINK_C
#if __option(a4_globals)
#define A4GLOBALS
#endif
#endif

#ifdef __MWERKS__
#if !__A5__
#define A4GLOBALS
#endif
#endif

#ifdef A4GLOBALS
#define GetGlobalsRegister GetRegisterA4
#define SetGlobalsRegister SetRegisterA4
#else
#define GetGlobalsRegister GetRegisterA5
#define SetGlobalsRegister SetRegisterA5
#endif

You can do a hell of a lot with completion routines, as long as you don't try to call QuickDraw, the Memory Manager, or make synchronous calls. The entire game of Bolo is basically one huge completion routine, which is why you can switch to Microsoft Word, pull down a menu, and sit there holding the mouse button down, without affecting the game of Bolo at all. That's why I've never really understood all the people who continuously complain that the Mac needs preemptive multi-tasking. Sure, preemptive multi-tasking makes the programming easier, but it doesn't fundamentally change what you can do. In fact it makes some things worse - with asynchronous I/O your completion routine gets called immediately when the operation is complete, where as with preemptive multi-tasking you're at the mercy of some scheduler that decides when your code next deserves to get a slice of CPU time.

Stuart Cheshire, cheshire@cs.stanford.edu

The Guiding Light

Not sure if I'm the first to point this out to you, but... I'm just looking at the "MacTech Now" ad on page 77 of the February issue. I see shadows behind the logo text at the top. And... The shadows don't match up! The ones behind the letters of the word "MacTech" indicate a light source above and to the left, but the ones behind the word "Now!" indicates a light source that's above and to the right!

Lawrence D'Oliveiro

Actually, Lawrence, the MacTechNOW logo was developed using an as yet unreleased QuickDraw3D derivative technology called QuickDrawMPV. This technology allows the simultaneous use of multiple points of view, resulting in shadows going in more than one direction. We chose to use QuickDrawMPV because it best represents how the MacTechNOW site provides information from more than one source.

We hope to offer more information about QuickDrawMPV in a future issue, assuming Apple doesn't see this technology as the joke it really is and refuse to acknowledge its existance.

Thanks for your note; I really wanted something like this for April, and you provided it. :-)

Eric Gundrum, Editor-in-Chief

More Beginning Articles, Please

Dear Editor,

I wanted to take a moment to respond to the Viewpoint article by Eric Gundrum in the December ‘96 issue.

I'm a subscriber that appreciates seeing articles targeted toward the beginning programmer. I can recall two recent articles that were of this category: Peter N. Lewis on memory issues and Mark Aldritt (I think) on tips for making AppleScripts run faster. It would be nice if each issue had one article targeted to beginners (a regular column?). My guess is that there is room for it, but most writers are less interested in the beginners audience. I don't know how many people (non-participants) read the programmer's challenge, but it seems to be one of the best opportunities for experienced programmers to learn new tricks and approaches. It's good that this department will be enhanced in future articles.

Mr. Gundrum also noted that more code examples would be given. Please stress that your authors should heavily comment their code. Also, wouldn't it be possible to archive the more detailed code on your website? That way you don't have to fill up your magazine pages with code, and the readers could retrieve it in digital form to avoid re-typing it. You could print a URL for that month's issue.

The vast majority of the magazine is over my head, but that's my own problem. I currently only have time to dabble - I'm working on trying to change that. The subscription is worth it to me just to stay abreast of what's happening.

Here are some suggestions for beginner's topics:

1) An article that addresses the upcoming changes to the MacOS and how a true beginner should prepare. (Admittedly, Apple is making it harder for you to anticipate the new OS.) I have purchased several beginners books that cover the current OS. However, I occasionally read about how the Event loop paradigm will change in MacOS 8. Then there's the scrapping of CDEVs and INITs. I worry that I'm learning things that will no longer be in use after another year or two. Are things going to change so much that it would be better to just wait, especially if the BeOS is adopted?

2) Surprisingly, I have not encountered a review of the binary foundation of programming in the Mac programming books. My ideal review would cover all the "lowest level" representations and their manipulation, such as octal, hexadecimal, setting bits, bit-wise shifts, etc. For example, while it's quite obvious to me why computers speak binary, I don't know what the value of hexadecimal is. I'm sure that seems like a very ignorant question to an experienced programmer. It may be typical from someone who was not a math or computer science major in college.

3) An article that addresses approaches to information storage (struct design): what are the best ways to store numbers, text, pictures, etc. Sample databases seem to be the best vehicle for illustrating these points. What should one think about in the design stage to ensure later speed and flexibility?

4) An article that focuses on GUI design: when I use Mac programs I often wonder how the programmers implement certain design features. Usually this entails linking underlying data to some element of the GUI - dragging list selections from a "source" to a "target", double-clicking a certain region to invoke an action. Another good example: in a full-featured word processing program that permits styling and coloring of text, how are these attributes stored when TextEdit is not being used? How does one calculate the physical dimensions of text data, ie. how do you implement a print preview function that gives a "to scale" WYSIWIG representation of the data? I realize that these are pretty advanced issues.

5) Manipulation of strings: sorting, searching, pattern matching, connection to the GUI (ie. double-clicking selects a word).

I'm sure I'll think of a few more...

Michael Myers

Michael, your point is well taken. The MacTech readership is a very diverse group, including nearly equal numbers of readers at all levels of programming expertise. I agree that every issue should include at least one more article for beginning programmers, and I am working with authors to get those articles written.

The complete project files for all of our articles are posted to the MacTech ftp site, available through MacTechNOW, when the issue ships. When asking an author to include code for an article, I ask that only enough of the code be included so the article can be read without your having to print pages of code from the ftp site. This leaves more space for explanations of the relevant points.

The articles you suggest are an excellent starting point. Keep those suggestions coming.

Eric Gundrum, Editor-in-Chief

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

CleanMyMac 3.8.1 - $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
Monolingual 1.7.8 - 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
Lyn 1.8.9 - Lightweight image browser an...
Lyn is a fast, lightweight image browser and viewer designed for photographers, graphic artists, and Web designers. Featuring an extremely versatile and aesthetically pleasing interface, it delivers... Read more
Tweetbot 2.5 - Popular Twitter client.
Tweetbot is a full-featured OS X Twitter client with a lot of personality. Whether it's the meticulously-crafted interface, sounds and animation, or features like multiple timelines and column views... Read more
BusyCal 3.1.7 - Powerful calendar app wi...
BusyCal is an award-winning desktop calendar that combines personal productivity features for individuals with powerful calendar sharing capabilities for families and workgroups. Its unique features... Read more
Adium 1.5.10.3 - Popular instant messagi...
Adium is a fast and free instant messaging client which supports AIM, ICQ, Jabber, MSN, Yahoo!, Google Talk, Yahoo! Japan, Bonjour, Gadu-Gadu, Novell Groupwise, SIP/SIMPLE (Text), and Lotus Sametime... Read more
Adium 1.5.10.3 - Popular instant messagi...
Adium is a fast and free instant messaging client which supports AIM, ICQ, Jabber, MSN, Yahoo!, Google Talk, Yahoo! Japan, Bonjour, Gadu-Gadu, Novell Groupwise, SIP/SIMPLE (Text), and Lotus Sametime... Read more
CleanMyMac 3.8.1 - $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
BusyCal 3.1.7 - Powerful calendar app wi...
BusyCal is an award-winning desktop calendar that combines personal productivity features for individuals with powerful calendar sharing capabilities for families and workgroups. Its unique features... Read more
Lyn 1.8.9 - Lightweight image browser an...
Lyn is a fast, lightweight image browser and viewer designed for photographers, graphic artists, and Web designers. Featuring an extremely versatile and aesthetically pleasing interface, it delivers... Read more

Latest Forum Discussions

See All

Ninja Pizza Girl (Games)
Ninja Pizza Girl 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: In the not-so-distant future, rampart traffic congestion has resulted in only one way to deliver pizzas across town in thirty... | Read more »
SCRAP (Games)
SCRAP 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: That day, for no apparent reason, SCRAP decided to wake up and run. He had to, because his activation was a mistake the "Factory" could... | Read more »
The Bunker (Games)
The Bunker 1.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.1 (iTunes) Description: The critically acclaimed console hit "The Bunker" comes to iOS, The groundbreaking live-action thriller adventure set in a real... | Read more »
Die With Glory (Games)
Die With Glory 1.2.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.2.0 (iTunes) Description: Die with Glory is an epic adventure game where your goal is to die in glorious fashion. You must help Sigurd, a brave old... | Read more »
Get Ike in the new Fire Emblem: Heroes u...
One of the most popular Fire Emblem characters is finally available in a new update to Nintendo'sFire Emblem: Heroes. [Read more] | Read more »
Die With Glory in a new viking adventure...
If you're a fan of classic adventure games you'll do well to pick upDie With Glory, the gorgeous new title from Cloud Castle inc. Die With Glory updatesthe gameplay of the same kind of adventure classics such asMonkey Island for modern, mobile... | Read more »
Get up to speed with everything you need...
In case you haven’t heard, MU Origin just got a colossal new update with new all-server events, battle modes, and systems making their way to the land of MU. Here’s a handy guide to everything you need to know about the latest content. [Read... | Read more »
Minimalist puzzle game, Cuts, free on iO...
If you're looking for a gorgeous puzzle experience on iOS devices, developer Gamebra.in's aesthetically interesting puzzler, Cuts, is discounted to free on the iOS App Store right now. [Read more] | Read more »
Anime tactical RPG, War of Crown, comes...
If you're looking for another tactical RPG fix to go alongside your Fire Emblem Heroes campaigns check out Gamevil's newest, anime-inspired tactics RPG, War of Crown, which comes out tomorrow. [Read more] | Read more »
Fantasy MMORPG MU Origin adds new modes,...
MU Origin, Webzen’s highly popular fantasy MMORPG is getting ready to shake things up for the second time this year, as a new update makes its way to the Google Play and App Store from today. Introducing new systems, modes, and events, the land of... | Read more »

Price Scanner via MacPrices.net

Digital Paper Tablet Offers Distraction Free...
I typically spend 8-10 hours a day gazing at the screens in my laptops and iPad, as tools of my livelihood, I don’t as a rule use electronic devices for pleasure reading. I subscribe to a daily... Read more
“Today at Apple” Bringing New Educational Ses...
Apple has announced plans to launch dozens of new educational sessions next month in all 495 Apple Stores ranging in topics from photo and video to music, coding, art and design, and more. The hands-... Read more
Smart Finance Free Comprehensive Personal Fin...
Moscow-based indie developer, Alexander Survillo has announced the release and immediate availability of Smart Finance: Personal Finance, Budget & Money 1.1.4, an update to his comprehensive... Read more
12-inch 1.1GHz Retina MacBooks on sale for $1...
B&H has 12″ 1.1GHz Retina MacBooks on sale for $100 off MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 12″ 1.1GHz Space Gray Retina MacBook: $1199.99 $100 off MSRP - 12... Read more
13-inch 2.7GHz Retina MacBook Pro on sale for...
B&H Photo has the 13″ 2.7GHz Retina MacBook Pro on sale for $130 off MSRP. Shipping is free, and B&H charges NY & NJ tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro (MF839LL/A): $1169 $... Read more
15-inch 2.2GHz Retina MacBook Pros available...
B&H Photo has the 15″ 2.2GHz Retina MacBook Pro available for $200 off MSRP including free shipping plus NY & NJ sales tax only: - 15″ 2.2GHz Retina MacBook Pro (MJLQ2LL/A): $1799.99 $200 off... Read more
13-inch Touch Bar MacBook Pros on sale for up...
B&H Photo has the 2016 Apple 13″ Touch Bar MacBook Pros in stock today for up to $150 off MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 13″ 2.9GHz/512GB Touch Bar... 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
12-inch 1.2GHz Retina MacBooks on sale for up...
B&H has 12″ 1.2GHz Retina MacBooks on sale for up to $160 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
HyperX Ships Pulsefire FPS Gaming Mouse, Winn...
Your reporter is a longtime fan of gaming mice for general purpose coomnputing use, finding them typically superior in comfort and performance. HyperX, a division of Kingston Technology Company, Inc... Read more

Jobs Board

*Apple* Mac Computer Technician - GeekHampto...
…complex computer issues over the phone and in person? GeekHampton, Long Island's Apple Premium Service Provider, is looking for you! Come work with our crew Read more
Product Manager, *Apple* Platforms - Viacom...
…Product Manager to drive the execution of its iOS and AppleTV experiences. The Apple Platform Product Manager will be a leader in our Agile/Scrum environment and Read more
Geek Squad *Apple* Master Consultation Agen...
**500662BR** **Job Title:** Geek Squad Apple Master Consultation Agent **Location Number:** 000286-Canton-Store **Job Description:** **What does a Geek Squad Read more
*Apple* Mobile Master - Best Buy (United Sta...
**500710BR** **Job Title:** Apple Mobile Master **Location Number:** 000279-North Olmsted-Store **Job Description:** **What does a Best Buy Apple Mobile Master Read more
*Apple* Engineering Specialist - CSRA (Unite...
Apple Engineering Specialist All times are in Eastern Daylight Time Requisition ID Job Locations US DC Washington DC Posted Date Category Engineering Sciences Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.