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

Viber 11.9.1 - Send messages and make fr...
Viber lets you send free messages and make free calls to other Viber users, on any device and network, in any country! Viber syncs your contacts, messages and call history with your mobile device, so... Read more
Vallum 3.3.2 - $15.00
Vallum is a little tool that helps you monitor and block apps connections and throttle apps bandwidth. It is able to intercept connections at the application layer, and hold them while you decide... Read more
Microsoft OneNote 16.31 - Free digital n...
OneNote is your very own digital notebook. With OneNote, you can capture that flash of genius, that moment of inspiration, or that list of errands that's too important to forget. Whether you're at... Read more
Apple Pages 8.2.1 - Apple's word pr...
Apple Pages is a powerful word processor that gives you everything you need to create documents that look beautiful. And read beautifully. It lets you work seamlessly between Mac and iOS devices, and... Read more
Numbers 6.2.1 - Apple's spreadsheet...
With Apple Numbers, sophisticated spreadsheets are just the start. The whole sheet is your canvas. Just add dramatic interactive charts, tables, and images that paint a revealing picture of your data... Read more
f.lux 39.9873 - Adjusts the color of you...
f.lux makes the color of your computer's display adapt to the time of day, warm at night and like sunlight during the day. Ever notice how people texting at night have that eerie blue glow? Or wake... Read more
Deeper 2.5.0 - Enable hidden features in...
Deeper is a personalization utility for macOS which allows you to enable and disable the hidden functions of the Finder, Dock, QuickTime, Safari, iTunes, login window, Spotlight, and many of Apple's... Read more
NTFS 15.5.71 - Provides full read and wr...
NTFS breaks down the barriers between Windows and macOS. Paragon NTFS effectively solves the communication problems between the Mac system and NTFS. Write, edit, copy, move, delete files on NTFS... Read more
MTR 5.3.0.0 - The Mac's oldest and...
MTR (was MacTheRipper)--the Mac's oldest and smartest DVD-backup app. MTR - the complete toolbox, not a one-trick, point-and-click extractor. MTR is intended for making fair-use, backup copies of... Read more
Keynote 9.2.1 - Apple's presentatio...
Easily create gorgeous presentations with the all-new Keynote, featuring powerful yet easy-to-use tools and dazzling effects that will make you a very hard act to follow. The Theme Chooser lets you... Read more

Latest Forum Discussions

See All

Black Desert Mobile gets an official rel...
Pearl Abyss has just announced that its highly-anticipated MMO, Black Desert Mobile, will launch globally for iOS and Android on December 11th. [Read more] | Read more »
Another Eden receives new a episode, cha...
Another Eden, WFS' popular RPG, has received another update that brings new story content to the game alongside a few new heroes to discover. [Read more] | Read more »
Overdox guide - Tips and tricks for begi...
Overdox is a clever battle royale that changes things up by adding MOBA mechanics and melee combat to the mix. This new hybrid game can be quite a bit to take in at first, so we’ve put together a list of tips to help you get a leg up on the... | Read more »
Roterra Extreme - Great Escape is a pers...
Roterra Extreme – Great Escape has been described by developers Dig-It Games as a mini-sequel to their acclaimed title Roterra: Flip the Fairytale. It continues that game's tradition of messing with which way is up, tasking you with solving... | Read more »
Hearthstone: Battlegrounds open beta lau...
Remember earlier this year when auto battlers were the latest hotness? We had Auto Chess, DOTA Underlords, Chess Rush, and more all gunning for our attention. They all had their own reasons to play, but, at least from where I'm standing, most... | Read more »
The House of Da Vinci 2 gets a new gamep...
The House of Da Vinci launched all the way back in 2017. Now, developer Blue Brain Games is gearing up to deliver a second dose of The Room-inspired puzzling. Some fresh details have now emerged, alongside the game's first official trailer. [Read... | Read more »
Shoot 'em up action awaits in Battl...
BattleBrew Productions has just introduced another entry into its award winning, barrelpunk inspired, BattleSky Brigade series. Whilst its previous title BattleSky Brigade TapTap provided fans with idle town building gameplay, this time the... | Read more »
Arcade classic R-Type Dimensions EX blas...
If you're a long time fan of shmups and have been looking for something to play lately, Tozai Games may have just released an ideal game for you on iOS. R-Type Dimensions EX brings the first R-Type and its sequel to iOS devices. [Read more] | Read more »
Intense VR first-person shooter Colonicl...
Our latest VR obsession is Colonicle, an intense VR FPS, recently released on Oculus and Google Play, courtesy of From Fake Eyes and Goboogie Games. It's a pulse-pounding multiplayer shooter which should appeal to genre fanatics and newcomers alike... | Read more »
PUBG Mobile's incoming update bring...
PUGB Mobile's newest Royale Pass season they're calling Fury of the Wasteland arrives tomorrow and with it comes a fair chunk of new content to the game. We'll be seeing a new map, weapon and even a companion system. [Read more] | Read more »

Price Scanner via MacPrices.net

Weekend Sale: Apple AirPods Pro for $234.98 a...
Abt Electronics has Apple’s new AirPods Pro in stock and on sale today for $234.98 including free shipping and free returns. Their price is $15 off Apple’s MSRP for these AirPods and tie Amazon... Read more
New 2019 16″ MacBook Pros on sale for $100 of...
Apple Authorized Reseller Adorama has new 2019 16″ MacBook Pros on sale today for $100 off Apple’s MSRP, each including free shipping. In addition, Adorama charges sales tax for NY & NJ residents... Read more
Apple Watch Series 3 GPS models on sale for l...
Amazon has Apple Watch Series 3 GPS models on sale starting at only $179. There prices are the lowest we’ve ever seen for these models from any Apple reseller. Choose Amazon as the seller rather than... Read more
iOS Bug In Facebook News Feed Lets Device Ca...
NEWS: 11.15.19- Users of the Facebook social media platform’s mobile app running on iOS devices won’t, like, this piece of news one bit in where a bug in the News Feed gave access to the camera... Read more
16″ MacBook Pros on sale! Preorder at Amazon...
Apple’s new 16″ MacBook Pros were only introduced yesterday, but Amazon is already offering a $100 discount on preorders. Prices for the base 6-Core 16″ MacBook Pros start at $2299: – 2019 16″ 2.6GHz... Read more
Use our exclusive MacBook Price Trackers to f...
Our Apple award-winning MacBook price trackers are the best place to look for the best sales & lowest prices on new and clearance MacBook Airs and MacBook Pros–including Apple’s new 16″ MacBook... Read more
New November Verizon iPhone deal: Get an iPho...
Verizon has the 64GB iPhone Xr on sale for 50% off for a limited time, plus they will include a free $200 prepaid MasterCard and a free Amazon Echo Dot. That reduces their price for the 64GB iPhone... Read more
Apple cuts prices on clearance, refurbished 2...
Apple has clearance 2018 15″ 6-Core Touch Bar MacBook Pros, Certified Refurbished, now available starting at only $1829. Each model features a new outer case, shipping is free, and an Apple 1-year... Read more
Up to $450 price drop on clearance 15″ MacBoo...
B&H Photo has dropped prices Apple’s 2019 15″ 6-Core and 8-Core MacBook Pros by $400-$450 off original MSRP, starting at $1999, with free overnight shipping available to many addresses in the US... Read more
Here’s how to save $200 on Apple’s new 16″ Ma...
Apple has released details of their Education discount associated with the new 2019 16″ 6-Core and 8-Core MacBook Pros. Take $200 off the price of the new 8-Core model (now $2599) and $200 off the 16... Read more

Jobs Board

Best Buy *Apple* Computing Master - Best Bu...
**746887BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Store Associates **Store NUmber or Department:** 001512-Ankeny-Store **Job Read more
Best Buy *Apple* Computing Master - Best Bu...
**746836BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Sales **Store NUmber or Department:** 000341-Scranton-Store **Job Description:** **What Read more
QA Manager, *Apple* - CBS Corporation (Unit...
# QA Manager, Apple **REF#:** 35331 **CBS BUSINESS UNIT:** CBS Interactive **JOB TYPE:** Full-Time Staff **JOB SCHEDULE:** **JOB LOCATION:** Burbank, CA **ABOUT Read more
*Apple* Mobility Pro - Best Buy (United Stat...
**744315BR** **Job Title:** Apple Mobility Pro **Job Category:** Store Associates **Store NUmber or Department:** 000662-Auburn AL-Store **Job Description:** At Best Read more
Nurse Practitioner - Field Based (San Bernard...
Nurse Practitioner - Field Based (San Bernardino, CA, Apple Valley, Hesperia) **Location:** **United States** **New** **Requisition #:** PS30312 **Post Date:** 4 Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.