TweetFollow Us on Twitter

September 93 - Letters

LETTERS

NEW TECH NOTE NUMBERS
In develop Issue 14 Peter Fink complains about the loss of Tech Note numbering. In your answer you write: "We're always open to suggestion, but so far you're the only one to mention this. If others reading this reply have similar feedback, I hope they'll let us know."

Actually, I and others have complained about the loss of Tech Note numbers for quite some time, but sometimes talking about these things is like complaining about the weather. I suspect most people just grumble along and don't complain in writing.
-- Johan G. E. Strandberg

Good news: Numbers are back; see the editorial on page 2 and the Tech Notes on this issue's CD. It's too bad when people grumble without writing; the latter is much more effective, and we really appreciate the effort. Thanks!
-- Caroline Rose

DEBUGGING LESSON FLUB
There seems to be a problem with the point made in the "Debugging Lesson" letter in the Letters section of develop Issue 14. According to the source listed, there would be no problem even if memory moved when FillWithData was called. Since the handle is being passed as a handle (that is, not dereferenced), and handles are 4-byte pointers (which get pushed onto the stack as is), FillWithData would always get a valid handle, which it can dereference internally to its heart's content.

Unfortunately, there seems to be a lot of confusion (and a great deal of paranoia) over the usage of handles. As long as you pass handles as handles (and watch your dereferencing), you'll be OK.
--Charlie Reading

Um, oops. (Imagine, if you will, me standing gaping and red-faced, astonished at my own carelessness and idiocy.)

You're right, of course; the danger is only in passing dereferenced handles to routines in other segments, and the code in the letter passes the handle itself. I guess I just read the text and didn't really look closely at the code before replying. Obviously, it was only intended as an example, and the writer's point is still valid: passing dereferenced handles to routines in other segments is dangerous. You should either pass the handle itself (as the example code did!) or lock the handle first.

Sorry about the confusion.
--Dave Johnson

BABBLING ON
I enjoyed reading Dave Johnson's column in develop Issue 13 ("Tower of Babble"). While reading his discussion of natural versus programming languages, I think I was able to put my finger on what has bugged me about HyperTalk® for years. Natural languages imply a fluidity of meaning, giving its users great flexibility for nuances, emphasis, and brevity. HyperTalk looks like a natural language, but it possesses none of that fluidity of meaning. In HyperCard ®, SET has but one meaning. But in my Oxford dictionary, "set" has 194 definitions! In other words, HyperCard looks so much like English, one winds up assuming that all kinds of structures could be used as long as they make sense in English (for example, "set me to true").

Allow me to submit a suggestion, which you may wish to pass along to the software gods. Since Apple has now all but declared that C and C++ are the only computer languages the human race will ever need, maybe it would be great to have a HyperTalk-to-C translator. Why? Well, C is a write- only language (no one ever can figure out what's happening in someone else's C listing) and HyperTalk is a read-only language (it's a cinch to understand, but impossible to code in). With a translator, we could write code that still could be understood, just like when we used to code in Pascal. (Yes, this is a joke, from a die-hard Pascal enthusiast.) Thanks again for a nifty column!
--Kevin Killion

I'm glad you liked the column. Your comment about HyperTalk is very well taken! I think that's what always bothered me about it, too, though it was just a sort of vague unease. Unfortunately, I think people who didn't learn "regular" programming languages first may have a distinct disadvantage: we "real" programmers know up front how limited and terse and strict programming languages are, and we don't expect anything more. But power users who learn HyperTalk (or, more likely now, AppleScript) as their very first programming language may be in for a struggle if they don't keep reminding themselves that it's not a natural language.

As a die-hard C enthusiast, I'll graciously ignore your slams against my favorite language, and assume that since you're obviously an intelligent person, sooner or later you'll realize the error of your ways and come around to the truth, bemoaning the years you've spent in bondage to an uptight compiler.
--Dave Johnson

ASYNCH SUPPORT ON A/UX
After reading through Jim Luther's Asynchronous Routines article in develop Issue 13, I spiffed up my application to make all my file handling asynchronous, anticipating the glorious day when all the drivers on my Macintosh support asynchronous calls. But since the SCSI Manager isn't asynchronous yet, there's no apparent difference to the user of my code (or to me, the hard-working programmer who wants payoff for my labors).

Is there any platform or configuration I can test my application on and see the results of my effort?
--Tony Amaretto

Try your code on A/UX 3.0.1 (the operating system for the Apple Workgroup Server 95); it features an enhanced File Manager that supports asynchronous calls to UNIX ® file systems simply by using the techniques in Jim Luther's article. AppleShare Pro takes advantage of this capability on AWS 95 to get performance up to four times better than AppleShare 3.0's under System 7 (your mileage, as always, will vary).

For more information related to the Asynchronus Routines article, see the box on the next page. Have fun!
--Dave Johnson

MORE ON ASYNCHRONOUS ROUTINES IN ISSUE 13

For developers interested in the "Asynchronous Routines on the Macintosh" article in develop Issue 13, here's some new information that has surfaced since then.

StackSpace. Contrary to the advice on page 28 of the article, you should not call StackSpace at interrupt time, because the Memory Manager might not be in a consistent state. Furthermore, StackSpace clears MemErr, which may have an adverse effect on the current process's handling of Memory Manager errors.

PPC polling. Unlike the Device Manager and File Manager, the PPC Toolbox stuffs the result of an asynchronous routine into ioResult before it's really done with the parameter block. If your interrupt code -- such as a VBL task -- polls ioResult periodically to check for completion and reuses the parameter block to make another call, the system can crash because one or more system queues will be corrupted.

Context switching. The System 7 Process Manager (and MultiFinder under System 6) will wait until all currently active asynchronous requests to the File Manager have completed before performing a context switch. This check was added for compatibility reasons to prevent system crashes caused by a few applications that accessed program globals within File Manager completion routines without restoring their A5 world. What this means to you is that if your application makes an asynchronous File Manager call and then calls WaitNextEvent or GetNextEvent, the system may wait for your call to complete. If the asynchronous File Manager call takes a long time to complete, it will appear to the user that the system isn't responding.

Synchronous drivers. Although you can execute low-level file access routines asynchronously, a volume's underlying device driver may not support asynchronous operations. Once the File Manager passes a request to a synchronous driver, that driver doesn't give up control until it has completed the task. Synchronous drivers (such as those using the current SCSI Manager) affect programs using asynchronous File Manager calls in two ways: unexpected pauses and unsightly stack frame buildup.

  • When calling the File Manager asynchronously, your program passes control to the File Manager and the request is placed in a queue or, if the queue is empty, the request is handled immediately. Either way, once a synchronous driver gets the request, it retains control until it has responded to the request. If the request takes a long time to complete, the user may think the system isn't responding. If your program is a background task, these pauses will affect the performance of the current foreground application. To keep this to a minimum, avoid time-consuming asynchronous File Manager requests.
  • Chaining asynchronous File Manager calls will work on volumes controlled by synchronous drivers, but watch out: When the driver is synchronous, the stack frames from the system and your completion routines will keep building up on the current stack until the last asynchronous call in the chain completes, or until the stack overwrites the current heap. You'll need to break the asynchronous File Manager call chain every few completion routines. A simple way to do this is to start a Time Manager or VBL task from your File Manager call's completion routine, and let the task start the next asynchronous File Manager call in the chain.

File Sharing and AppleShare. Chained asynchronous File Manager calls can fail when either the Macintosh File Sharing or AppleShare 3.0 (not 3.0.1) file server is running. The file server software intercepts almost all calls made to the File Manager. Due to how the file server keeps track of what requests it has or hasn't seen, there are a few situations where the file server can do the wrong thing with chained asynchronous File Manager calls. To make sure the file server sees and handles all chained asynchronous File Manager calls correctly, use two parameter blocks for the chained calls and switch parameter blocks at every completion routine.


WE HATE IT WHEN YOU DON'T WRITE We welcome timely letters to the editors, especially from readers reacting to articles that we publish in develop. Letters should be addressed to Caroline Rose (or, if technical develop-related questions, to Dave Johnson) at Apple Computer, Inc., 20525 Mariani Avenue, M/S 303-4DP, Cupertino, CA 95014 (AppleLink CROSE or JOHNSON.DK). All letters should include your name and company name as well as your address and phone number. Letters may be excerpted or edited for clarity (or to make them say what we wish they did). *

SUBSCRIPTION INFORMATIONSubscriptions to develop are available through APDA (see inside back cover for APDA information), or you can use the subscription card in the back of this issue. Please address all subscription-related inquiries to develop, Apple Computer, Inc., P.O. Box 531, Mt. Morris, IL 61054 (or AppleLink DEV.SUBS). *

BACK ISSUES For information about back issues of develop and how to obtain them, see the last page of this issue. Back issues are also on the develop Bookmark CD and the Developer CD Series disc (Reference Library edition).*

Thanks to François Grieu and Lawrence D'Oliveiro for providing some of this information. *

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Kill the Plumber World guide - How to ou...
You already know how to hop around like Mario, but do you know how to defeat him? Those are your marching orders in Kill the Plumber, and it's not always as easy as it looks. Here are some tips to get you started. This is not a seasoned platform... | Read more »
Planar Conquest (Games)
Planar Conquest 1.0 Device: iOS Universal Category: Games Price: $12.99, Version: 1.0 (iTunes) Description: IMPORTANT: Planar Conquest is compatible only with iPad 3 & newer devices, iPhone 5 & newer. It’s NOT compatible with... | Read more »
We talk to Cheetah Mobile about its plan...
Piano Tiles 2 is a fast-paced rhythm action high score chaser out now on iOS and Android. You have to tap a series of black tiles that appear on the screen in time to the music, being careful not to accidentally hit anywhere else. Do that and it's... | Read more »
Ultimate Briefcase guide - How to dodge...
Ultimate Briefcase is a simple but tricky game that’s highly dependent on how fast you can react. We can still offer you a few tips and tricks on how to survive though. Guess what? That’s exactly what we’re going to do now. Take it easy [Read more... | Read more »
SoundPrism Link Edition (Music)
SoundPrism Link Edition 1.0 Device: iOS Universal Category: Music Price: $4.99, Version: 1.0 (iTunes) Description: ***Introductory price for a the first few days after launch - if you're reading this, get it while it's fresh out of... | Read more »
Pre-register now for hack and slasher An...
Fincon, which won Facebook's Studio to Watch award in 2015, has announced that pre-registration is now open for the massive 3.0 update for its award-winning hack and slasher Angel Stone. Angel Stone is a post-apocalyptic action RPG in which the... | Read more »
Google has named Piano Tiles 2 as its Be...
Google has named Piano Tiles 2, which launched back in August last year, as its Best Game of 2015. If you're yet to play it, now's a good time to do so. It's a sequel to the hugely successful viral hit Piano Tiles (Don't Tap the White Tile) but... | Read more »
Sago Mini Trucks and Diggers (Education...
Sago Mini Trucks and Diggers 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: Drive a dump truck with Rosie the hamster! Pile dirt high and dig deep in the ground with diggers, cranes and... | Read more »
Day One 2 Journal + Notes (Lifestyle)
Day One 2 Journal + Notes 2.0 Device: iOS Universal Category: Lifestyle Price: $4.99, Version: 2.0 (iTunes) Description: **New Release Sale—50% off for a Limited Time!** Capture life as you live it. From once-in-a-lifetime events to... | Read more »
Pull My Tongue (Games)
Pull My Tongue 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Meet Greg. A hungry little chameleon that loves popcorn! Help feed Greg by pulling his tongue through a series of fun puzzles... | Read more »

Price Scanner via MacPrices.net

Watch Super Bowl 50 Live On Your iPad For Fre...
Watch Super Bowl 50 LIVE on the CBS Sports app for iPad and Apple TV. Get the app and then tune in Sunday, February 7, 2016 at 6:30 PM ET to catch every moment of the big game. The CBS Sports app is... Read more
Two-thirds Of All Smart Watches Shipped In 20...
Apple dominated the smart watch market in 2015, accounting for over 12 million units and two-thirds of all shipments according to Canalys market research analysts’ estimates. Samsung returned to... Read more
12-inch 1.2GHz Retina MacBooks on sale for up...
B&H Photo has 12″ 1.2GHz Retina MacBooks on sale for $180 off MSRP. Shipping is free, and B&H charges NY tax only: - 12″ 1.2GHz Gray Retina MacBook: $1499 $100 off MSRP - 12″ 1.2GHz Silver... Read more
12-inch 1.1GHz Gray Retina MacBook on sale fo...
B&H Photo has the 12″ 1.1GHz Gray Retina MacBook on sale for $1199 including free shipping plus NY sales tax only. Their price is $100 off MSRP, and it’s the lowest price available for this model... Read more
Apple now offering full line of Certified Ref...
Apple now has a full line of Certified Refurbished 2015 21″ & 27″ iMacs available for up to $350 off MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are... Read more
Free GUI Speedometer – The Ultimate Digital D...
Miami, Florida based RMKapps has announced the official release of GUI Speedometer 1.0, their digital dashboard display developed for iOS devices. GUI Speedometer allows users to track their precise... Read more
FutureCalc: Ergonomic iOS Calculator App For...
London, United Kingdom based Independent software developer and entrepreneur, Hovik Melikyan has announced the release and immediate availability of FutureCalc 1.0, his new ergonomic calculator app... Read more
Save up to $600 with Apple refurbished Mac Pr...
Apple has Certified Refurbished Mac Pros available for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The following... Read more
Apple’s ‘Next Big Thing’ Drought And Mature M...
Apple’s first fiscal quarter 2016 financial results yielded both good news and bad news. In the positive column, Apple made another boatload of money, reporting record quarterly revenue of $75.9... Read more
Lifeproof NUUD For iPhone 6S, iPhone 6S Plus...
LifeProof NUUD was designed to defy more than the elements. It defies logic itself by combining legendary four-proof protection and screenless technology to survive mountaintop missions and seaside... Read more

Jobs Board

*Apple* Macintosh OSX - Net2Source Inc. (Uni...
…: * Work Authorization : * Contact Number(Best time to reach you) : Skills : Apple Macintosh OSX Location : New York, New York. Duartion : 6+ Months The associate would Read more
Computer Operations Technician ll - *Apple*...
# Web Announcement** Apple Technical Liaison**The George Mason University, Information Technology Services (ITS), Technology Support Services, Desktop Support Read more
Restaurant Manager - Apple Gilroy Inc./Apple...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
Simply Mac *Apple* Specialist- Service Repa...
Simply Mac is the largest premier retailer of Apple products in the nation. In order to support our growing customer base, we are currently looking for a driven Read more
*Apple* IOS / OS X Level 3 Support Analyst -...
Needed: Apple Support Analyst (OS X / IOS); 50k-60k/yr +…Horizon Technology Partners has an immediate opening for an Apple IOS / OS X LEVEL 3 Support Analyst. Your Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.