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

GraphicConverter 10.5.1 - $39.95
GraphicConverter is an all-purpose image-editing program that can import 200 different graphic-based formats, edit the image, and export it to any of 80 available file formats. The high-end editing... Read more
Delicious Library 3.7 - Import, browse a...
Delicious Library allows you to import, browse, and share all your books, movies, music, and video games with Delicious Library. Run your very own library from your home or office using our... Read more
Adobe Animate CC 2017 18.0.0.107 - Anima...
Animate CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Flash Professional customer). Animate CC 2018 (was Flash CC) lets you... Read more
Adobe After Effects CC 2018 15.0 - Creat...
After Effects CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous After Effects customer). The new, more connected After Effects CC... Read more
Adobe Premiere Pro CC 2018 12.0.0 - Digi...
Premiere Pro CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Premiere Pro customer). Adobe Premiere Pro CC 2018 lets you edit... Read more
Alarm Clock Pro 10.3 - $19.95
Alarm Clock Pro isn't just an ordinary alarm clock. Use it to wake you up in the morning, send and compose e-mails, remind you of appointments, randomize the iTunes selection, control an internet... Read more
Adobe Lightroom 20170919-1412-ccb76bd] -...
Adobe Lightroom is available as part of Adobe Creative Cloud for as little as $9.99/month bundled with Photoshop CC as part of the photography package. Lightroom 6 is also available for purchase as a... Read more
Adobe Illustrator CC 2018 22.0.0 - Profe...
Illustrator CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Illustrator customer). Adobe Illustrator CC 2018 is the industry... Read more
Hopper Disassembler 4.3.0- - Binary disa...
Hopper Disassembler is a binary disassembler, decompiler, and debugger for 32- and 64-bit executables. It will let you disassemble any binary you want, and provide you all the information about its... Read more
Adobe InDesign CC 2018 13.0.0.125 - Prof...
InDesign CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous InDesign customer). Adobe InDesign CC 2018 is part of Creative Cloud.... Read more

ICEY (Games)
ICEY 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: ICEY is a 2D side-scrolling action game. As you follow the narrator's omnipresent voice, you will see through ICEY's eyes and learn the... | Read more »
The best new games we played this week -...
We've made it, folks. Another weekend is upon us. It's time to sit back and relax with the best new releases of the week. Puzzles, strategy RPGs, and arcade games abound this week. There's a lot of quality stuff to unpack this week, so let's hop... | Read more »
Wheels of Aurelia (Games)
Wheels of Aurelia 1.0.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0.1 (iTunes) Description: | Read more »
Halcyon 6: Starbase Commander guide - ti...
Halcyon 6 is a well-loved indie RPG with stellar tactical combat and some pretty good writing, too. It's now landed on the App Store, so mobile fans, if you're itching for a good intergalactic adventure, here's your game. Being a strategy RPG, the... | Read more »
Game of Thrones: Conquest guide - how to...
Fans of base building games might be excited to know that yet another entry in the genre has materialized - Game of Thrones: Conquest. Yes, you can now join the many kingdoms of the famed book series, or create your own, as you try to conquer... | Read more »
Halcyon 6: Starbase Commander (Games)
Halcyon 6: Starbase Commander 1.4.2.0 Device: iOS Universal Category: Games Price: $6.99, Version: 1.4.2.0 (iTunes) Description: An epic space strategy RPG with base building, deep tactical combat, crew management, alien diplomacy,... | Read more »
Legacy of Discord celebrates its 1 year...
It’s been a thrilling first year for fans of Legacy of Discord, the stunning PvP dungeon-crawling ARPG from YOOZOO Games, and now it’s time to celebrate the game’s first anniversary. The developers are amping up the festivities with some exciting... | Read more »
3 reasons to play Thunder Armada - the n...
The bygone days of the Battleship board game might have past, but naval combat simulators still find an audience on mobile. Thunder Armada is Chinese developer Chyogames latest entry into the genre, drawing inspiration from the explosive exchanges... | Read more »
Experience a full 3D fantasy MMORPG, as...
Those hoping to sink their teeth into a meaty hack and slash RPG that encourages you to fight with others might want to check out EZFun’s new Eternity Guardians. Available to download for iOS and Android, Eternity Guardians is an MMORPG that lets... | Read more »
Warhammer Quest 2 (Games)
Warhammer Quest 2 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Dungeon adventures in the Warhammer World are back! | Read more »

Price Scanner via MacPrices.net

9″ iPads on sale for $30 off, starting at $29...
MacMall has 9″ iPads on sale for $30 off including free shipping: – 9″ 32GB iPad: $299 – 9″ 128GB iPad: $399 Read more
Apple restocks full line of refurbished 13″ M...
Apple has restocked a full line of Apple Certified Refurbished 2017 13″ MacBook Pros for $200-$300 off MSRP. A standard Apple one-year warranty is included with each MacBook, and shipping is free.... Read more
13″ 3.1GHz/256GB MacBook Pro on sale for $167...
Amazon has the 2017 13″ 3.1GHz/256GB Space Gray MacBook Pro on sale today for $121 off MSRP including free shipping: – 13″ 3.1GHz/256GB Space Gray MacBook Pro (MPXV2LL/A): $1678 $121 off MSRP Keep an... Read more
13″ MacBook Pros on sale for up to $120 off M...
B&H Photo has 2017 13″ MacBook Pros in stock today and on sale for up to $120 off MSRP, each including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Space Gray MacBook... Read more
15″ MacBook Pros on sale for up to $200 off M...
B&H Photo has 15″ MacBook Pros on sale for up to $200 off MSRP. Shipping is free, and B&H charges sales tax in NY & NJ only: – 15″ 2.8GHz MacBook Pro Space Gray (MPTR2LL/A): $2249, $150... Read more
Roundup of Apple Certified Refurbished iMacs,...
Apple has a full line of Certified Refurbished 2017 21″ and 27″ iMacs available starting at $1019 and ranging up to $350 off original MSRP. Apple’s one-year warranty is standard, and shipping is free... Read more
Sale! 27″ 3.8GHz 5K iMac for $2098, save $201...
Amazon has the 27″ 3.8GHz 5K iMac (MNED2LL/A) on sale today for $2098 including free shipping. Their price is $201 off MSRP, and it’s the lowest price available for this model (Apple’s $1949... Read more
Sale! 10″ Apple WiFi iPad Pros for up to $100...
B&H Photo has 10.5″ WiFi iPad Pros in stock today and on sale for $50-$100 off MSRP. Each iPad includes free shipping, and B&H charges sales tax in NY & NJ only: – 10.5″ 64GB iPad Pro: $... Read more
Apple iMacs on sale for up to $130 off MSRP w...
B&H Photo has 21-inch and 27-inch iMacs in stock and on sale for up to $130 off MSRP including free shipping. B&H charges sales tax in NY & NJ only: – 27″ 3.8GHz iMac (MNED2LL/A): $2179 $... Read more
2017 3.5GHz 6-Core Mac Pro on sale for $2799,...
B&H Photo has the 2017 3.5GHz 6-Core Mac Pro (MD878LL/A) on sale today for $2799 including free shipping plus NY & NJ sales tax only . Their price is $200 off MSRP. 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
Commerce Engineer, *Apple* Media Products -...
Commerce Engineer, Apple Media Products (New York City) Job Number: 113028813New York City, New York, United StatesPosted: Sep. 20, 2017Weekly Hours: 40.00 Job Read more
US- *Apple* Store Leader Program - Apple (Un...
US- Apple Store Leader Program Job Number: VariousUnited StatesPosted: Oct. 19, 2017Retail Store Job Summary Learn and grow as you explore the art of leadership at Read more
Product Manager - *Apple* Pay on the *Appl...
Job Summary Apple is looking for a talented product manager to drive the expansion of Apple Pay on the Apple Online Store. This position includes a unique Read more
*Apple* Retail - Multiple Positions - Farmin...
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
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.