TweetFollow Us on Twitter

Feb 90 Letters
Volume Number:6
Issue Number:2
Column Tag:Letters

CheckAbort() Revised

By David E. Smith, Editor & Publisher, MacTutor

Let’s Doodat!

Greg King, Ph.D.

SCIEX

Ontario, Canada

This letter is to point out 2 bugs in Lee Neuse’s “check_abort” routine (Three Doodats, Sept. 89).

The first bug occurs when the command period event is the last event in the queue. Mr. Neuse’s code removes the event and then tests to see if it was the last event. This will never succeed because the event has been removed. The result is usually a bus error because the qLink field of the last event contains a -1. The funny thing is that the routine will not crash if the command-period is the only event in the queue.

The second bug is more subtle. Dequeue does not de-allocate the memory for the event entry being removed from the queue, this is the responsibility of the program calling it (IM2-383). Mr. Neuse doesn’t do this so every time an event is removed it hangs around the heap.

Below is my version of a command-period handler that addresses the above stated problems. It has been tested for the past week in the print and update loops of a 400K application. It is a scientific application that often has to plot many thousands of data points on the screen, and it is often desirable to be able to both abort long updates and queue up multiple keystroke commands. Please excuse my style, I was originally a Pascal programmer.

/* 1 */

Boolean CmdPeriod()
{
EvQElPtreq_p, theEntry;
Boolean f_found, last, dispose_entry;

f_found = FALSE;
last = FALSE;

/* Start at head of internal queue. */
eq_p = (EvQElPtr) (EventQueue.qHead);

do {
 /* Test for end of queue first. */
 if (eq_p == (EvQElPtr) EventQueue.qTail)
 last = TRUE;

 /* Is this a cmd-period event. */
 if ((eq_p->evtQWhat == keyDown 
 || eq_p->evtQWhat == autoKey) 
 && (eq_p->evtQModifiers & cmdKey) 
 && (eq_p->evtQMessage & charCodeMask) == ‘.’)
 {
 /* Remove the event from the queue. */
 Dequeue((QElemPtr) eq_p, &EventQueue);
 f_found = TRUE;
 /* Setup for disposal */
 dispose_entry = TRUE;
 /* Point to the beginning of entry. */
 theEntry = (EvQElPtr) ((long) eq_p - 4);
 }
 else
 dispose_entry = FALSE;
 
 if (!last)
 /* Continue with next queue entry. */
 eq_p = (EvQElPtr) (eq_p->qLink);

 /* Dequeue doesn’t deallocate entry */
 if (dispose_entry)
 DisposPtr((Ptr) theEntry);
 }
while (!last);

return (f_found);
}

On the whole, I found Mr. Neuse’s article well written and informative.

SCIEX is a Canadian company that produces high end mass spectrometers for environmental, security, biotech, and research applications. Our latest product uses a Macintosh II for data aquisition and processing. We are dedicated to using the Macintosh for scientific applications.

Let’s Doodat Again

J. Peter Alfke

Tucson, AZ

The idea of “doodats” as presented by Lee A. Neuse (“Three Doodats”, September 1989, p. 82) is a good one. Unfortunately, the checkAbort() doodat (which checks for Cmd-”.”) has at least two bugs, one apparently harmless, the other fatal.

The harmless bug concerns the most common case: an empty event. As written, checkAbort() charges ahead and examines the event-queue element pointed to by EventQueue.qTail. Unfortunately, if the event queue is empty this value is NIL. Fortunately, whatever data is at NIL doesn’t usually look like a Cmd-”.” keypress, and the routine exits with false.

But consider another case: there are at least two entries in the queue, the last of which is a bona-fide Cmd-”.”. The last queue entry gets dequeued and then checked to see if it matches EventQueue.qTail. Of course, it can never match since it was just removed from the queue. So the routine always goes around again to the next queue element. But the next element is reference through the old one’s qLink field, which is NIL since it was the last entry in the queue.

Now we are looking at the queue entry at NIL, just like in the other bug, But this time EventQueue.qTail isn’t conveniently NIL (it’s pointing to the last remaining event) so we jump to the next entry instead of exiting. This involves dereferencing NIL and we are on a runaway journey to Bus Error Land.

After sitting in the THINK C debugger for a while figuring all this out. I came up with a revised version, as shown below:

/* 2 */

bool
checkAbort(void)
{
 EvQElPtr q, nextq;
 bool last;
 bool found = false;

 q = (EvQElPtr) EventQueue.qHead;
 if (q) /* Ignore empty event queue */
 do {
 last = (q == (EvQElPtr) EventQueue.qTail); /* Last event? */
 nextq = (EvQEl*) q->qLink; /* the next one */
 if ((q->evtQWhat == keyDown || q-> evtQWhat == autoKey) && q->evtQModifiers 
& cmdKey 
 && (q->evtQModifiers & shiftKey) == 0
 && (q->evtQMessage & charCodeMask) == ‘.’) {
 Dequeue(q, &EventQueue);
 found = true;
 }
 q = nextq;
 } while (!last);
 
 return found;
}

My routine also ignores Cmd-Shift-”.” (i.e. Cmd-”>”), which many applications (such as mine, along with Microsoft Word) uses as an Increment-Point-Size command.

Doodat One More Time

Joe Rice

Doodat #1 in your C Workshop feature in the September issue encouraged me to implement a solution to a problem we were having in the application on which I’m currently working. In some areas of our application, we’re running real-time loops that cannot afford to be interrupted by Multifinder yet need to be able to test for several events, not just Cmd-Period. While the sample code provided an excellent starting, it had a few bugs.

First, it doesn’t check for an empty queue before plunging into the loop.

Second, it retrieves a value (qLink) from the queue element pointed to by eq_p after the element has potentially been dequeued.

Third, dequeuing elements from the EventQueue confuses the Event Manager big time. My guess is that when the Event Manager dequeues an element, it probably enqueues that element outside onto a queue of “free” elements so that it can be reused. Dequeuing the element outside of the Event Manager appears to shorten the EventQueue permanently causing the application to grind to a halt within short order. The solution is to change the event to a null event rather than dequeuing it.

The code that we implemented is below. It’s organized somewhat differently than the example code in MacTutor so that it would be a bit more general.

/* 3 */

/**********************
Name:  CheckForEvent
Purpose:  check the event queue for an event without calling Get/WaitNextEvent. 
 Note that this routine removes all events which pass the test from the 
Event queue, not just the first.

TestMDown and TestCmdPeriod are two TestProcs for CheckForEvent.

CheckForEvent((ProcPtr) TestMDown) will return TRUE if the mouse has 
been clicked.

CheckForEvent((ProcPtr) TestCmdPeriod) will return TRUE if a Cmd-Period 
has been typed.
**********************/

Boolean CheckForEvent(TestProc)
ProcPtr TestProc;
{
EvQElPtreqPtr, nextEqPter;
Boolean found;
OSErr status;

found = FALSE;

eqPtr = (EvQElPtr) (EventQueue.qHead);
while (eqPtr != 0) {
 if ((*TestProc) (eqPtr)) {
 eqPtr->evtQWhat = nullEvent;
 found = TRUE;
 }

 if (eqPtr == (EvQElPtr) EventQueue.qTail)
 break;
 
 eqPtr = (EvQEl *) (eqPtr->qLink);
 }
return found;
}

Boolean TestCmdPeriod (eqPtr)
EvQElPtreqPtr;
{
if ((eqPtr->evtQWhat == keyDown 
 || eqPtr->evtQWhat == autoKey) 
 && (eqPtr->evtQModifiers & cmdKey) 
 && (eqPtr->evtQMessage & charCodeMask) == ‘.’)
 return TRUE;

return FALSE;
}

Boolean TestMDown (eqPtr)
EvQElPtreqPtr;
{
if ((eqPtr->evtQWhat == mouseDown)
 return TRUE;

return FALSE;
}

[Although each of the three previous letters deal with the bug in the original article. I thought their solutions were interesting in their own right to be printed here. The first letter dealt with deallocation of memory. The second deals with Cmd-’.’ over Cmd-’>’. The third takes a unique approach by setting the event type to null rather than removing the event. It also gives a mouse down event remover.-ed]

Ken Manly

Buffalo Chip Software

Buffalo, NY

Your readers may be amused by an ‘undocumented feature’ that Forrest Tanaka (MacDTS) and I discovered. If you create an Apple menu using ResEdit, there are two ways you can type the apple symbol into the menu title field. If you type control-T, the value stored will be $14, and all will be well.

If you type shift-command-K (which is what Key Caps suggests) you will get a menu which looks and acts like an Apple menu, but it is not recognized by Notification Manager routines (in System 6.x). The first symptom is that when your alarm clock goes off while your application is running, the alarm icon (which should alternate with the apple) never appears. Thanks to Forrest for guessing there was something wrong with my apple, although he had no way of knowing what.

ADB??

Kirk Chase

Anaheim CA

It seems someone did not know what the acronym “ADB” meant in a recent article. “ADB” stands for “Apple’s Desktop Bus”. It was introduced with the new keyboard. It allows the chaining of serial devices such as keyboards, mice, tablets, and so on to the Mac.

If you would like more information on ADB, there is an article by Dave Kelly and David Smith in the March '89 issue. It explains some of the concepts. It also references Tech Note #206. You can also find information on the Apple Desktop Bus in Inside Macintosh Vol. V.

MacFortran subroutines from MPW Assembler

Bob Robinson

Plainfield NJ 07060

One of the first things I needed after buying MPW was a way to get the files from the assembler into a format that could be used as a subroutine by Absoft MacFortran (chemists aren’t instructed in ‘C’ in college or grad school.) MacFortran subroutines can be speeded up dramatically (also true of other languages) by hand-tuning the compiler’s assembly language output. The Fortran program listed below strips out the unneeded bytes from the MPW assembler object file. The resulting file is callable from MacFortran as a subroutine, which can be loaded dynamically or linked in with the main program. Also listed below is a short assembly language Fortran function for compilation by MPW. The function locks down a Mac memory manager handle and returns a pointer. MacFortran expects function results to be returned in register D0, so the subroutine must save the result in D0 before exiting (the toolbox traps used here happen to use D0.) If it’s to be loaded dynamically by MacFortran, the subroutine must preserve A0. Note: makesub displays the subroutine name in the menu bar, to avoid the Fortran TTY window (compile with ‘O’ option.)

*4

*****************************************************************************************
 program makesub
* R.S. Robinson 6/12/89
* Converts MPW Asm ‘.a.o’ files into MacFortran ‘.sub’ files.
* File name is obtained from clipboard.
* Removes 1st 36 bytes, and last 8 bytes (44 bytes smaller)
 implicit none   ! always a good idea
 include toolbx.par! MacFortran toolbox definitions
 integer i,j,toolbx,htoptr,length,scrap_h,scrapptr
 integer*1 subr(16384)  ! can make bigger if needed
 character*6 fname ! subroutine names always ¾ 6 chars long plus ‘.sub’
 logical*4 exists! error checking
 scrap_h=toolbx(NEWHANDLE,0)! needs a dummy handle
 length=toolbx(GETSCRAP,scrap_h,”TEXT”,i)    ! we don’t use i
* funct ‘htoptr’ locks handle & returns 32bit comptble ptr;
* or use toolbox calls: call toolbx(HLOCK,scrap_h);scrapptr=LONG(scrap_h)
 scrapptr=htoptr(scrap_h)
 fname=’’;if (length>6) length=6
 do (i=1,length);fname(i:i)=CHAR(BYTE(scrapptr+i-1));repeat
 call toolbx(HUNLOCK,scrap_h) ! finished with the scrap, release the 
handle
 inquire (file=TRIM(fname)//’.a.o’,exist=exists)
 if (.NOT.exists) stop
 call toolbx(INSERTMENU,toolbx(NEWMENU,20,char(length)//fname),0)
 call toolbx(DRAWMENUBAR) ! show that we found the file
 open(20,file=fname//’.a.o’,form=’unformatted’,recl=1)
 do (i=1,36);read(20,end=100) subr(i);repeat ! skip 1st 36 bytes
 do (i=1,16384);read(20,end=100) subr(i);repeat ! read the ‘.a.o’ file
100close(20);i=i-9 ! ignore last 8 bytes plus loop overrun
 open(20,file=fname//’.sub’,status=’new’,form=’unformatted’,recl=1)
 do (j=1,i);write(20) subr(j);repeat;close(20) ! write ‘.sub’ file
 end

*****************************************************************************************
* Assemble the code below with MPW Asm, then run ‘makesub’ after copying 
‘htoptr’
* to the clipboard in MPW. The ‘makesub’ program will produce a MacFortran-compatible
* subroutine from the MPW ‘a.o’ file. As set up here, ‘makesub’ must 
be in the same
* folder as the ‘.a.o’ file. The MPW command sequence is:
*
*(copy ‘htoptr’ to clipboard, then)
*Asm [pathname:]htoptr.a
*[pathname:]makesub (must remove ‘ apl’ extension from Fortran program)
*
;integer*4 function htoptr(handle)
; R.S. Robinson 6/12/89
; Takes ‘handle’ as argument, returns locked pointer as function result.
; Function results are obtained by MacFortran from register D0.
;
 INCLUDE ‘Traps.a’ ; MPW equates
Start PROC; needed for MPW
HTOPTR: MOVE.L A0,A2 ; preserve A0 for MacFortran
 MOVEA.L4(A7),A0 ; load pointer to ‘handle’ argument
 MOVE.L (A0),A0  ; load ‘handle’
 _MoveHHi ; move handle to top of heap zone
 _HLock ; lock it
 MOVE.L (A0),D0  ; convert to pointer, ready to strip
 _StripAddress   ; it’s now ’32-bit clean;’ result is in D0
 MOVE.L A2,A0    ; restore A0
 RTS    ; all done; return to Fortran
 END

 
AAPL
$111.01
Apple Inc.
+1.60
MSFT
$46.98
Microsoft Corpora
+1.24
GOOG
$509.20
Google Inc.
+4.31

MacTech Search:
Community Search:

Software Updates via MacUpdate

BBEdit 11.0.2 - Powerful text and HTML e...
BBEdit is the leading professional HTML and text editor for the Mac. Specifically crafted in response to the needs of Web authors and software developers, this award-winning product provides a... Read more
ExpanDrive 4.2.1 - Access cloud storage...
ExpanDrive builds cloud storage in every application, acts just like a USB drive plugged into your Mac. With ExpanDrive, you can securely access any remote file server directly from the Finder or... Read more
Adobe After Effects CC 2014 13.2 - Creat...
After Effects CC 2014 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). After Effects CS6 is still available... Read more
Command-C 1.1.7 - Clipboard sharing tool...
Command-C is a revolutionary app which makes easy to share your clipboard between iOS and OS X using your local WiFi network, even if the app is not currently opened. Copy anything (text, pictures,... Read more
Tidy Up 4.0.2 - Find duplicate files and...
Tidy Up is a complete duplicate finder and disk-tidiness utility. With Tidy Up you can search for duplicate files and packages by the owner application, content, type, creator, extension, time... Read more
Typinator 6.3 - Speedy and reliable text...
Typinator turbo-charges your typing productivity. Type a little. Typinator does the rest. We've all faced projects that require repetitive typing tasks. With Typinator, you can store commonly used... Read more
GraphicConverter 9.5 - Graphics editor w...
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
Toast Titanium 12.0.1 - The ultimate med...
Toast Titanium goes way beyond the very basic burning in the Mac OS and iLife software, and sets the standard for burning CDs, DVDs, and now Blu-ray discs on the Mac. Create superior sounding audio... Read more
QuickBooks 2015 16.0.2.1422 R3 - Financi...
Save 20% on QuickBooks Pro for Mac today through this special discount link QuickBooks Pro 2013 helps you manage your business easily and efficiently. Organize your finances all in one place, track... Read more
Remotix 3.0.6 - Access all your computer...
Remotix is a fast and powerful application to easily access multiple Macs (and PCs) from your own Mac. Features: Complete Apple Screen Sharing support - including Mac OS X login, clipboard... Read more

Latest Forum Discussions

See All

Brothers in Arms 3: Sons of War Review
Brothers in Arms 3: Sons of War Review By Jennifer Allen on December 18th, 2014 Our Rating: :: FUN BUT PUSHYUniversal App - Designed for iPhone and iPad Brothers in Arms 3: Sons of War could be great fun, but its plethora of... | Read more »
The Snow is Falling on the French Countr...
The Snow is Falling on the French Countryside of Carcassonne’s Newest Update Posted by Jessica Fisher on December 18th, 2014 [ permalink ] < | Read more »
Creatures Such As We Review
Creatures Such As We Review By Jennifer Allen on December 18th, 2014 Our Rating: :: INTERESTING DISCUSSIONSUniversal App - Designed for iPhone and iPad Taking a more sedate approach to interactive fiction, Creatures Such As We... | Read more »
Stair: Slide the Blocks to Ascend (Game...
Stair: Slide the Blocks to Ascend 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Slide the blocks to ascend! Stair: Slide the Blocks to Ascend | Read more »
Give It Up! (Games)
Give It Up! 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: GIVE IT UP is a rather hard game where you have to assist this cheerful, singing Blob in jumping through 9 different tracks.So far... | Read more »
The Drive : Devil's Run (Games)
The Drive : Devil's Run 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: ON THE ROAD AGAIN! The Drive - Devil’s Run is classic point to point style racing game that pays homage to the classics... | Read more »
Procreate Pocket (Entertainment)
Procreate Pocket 1.01 Device: iOS iPhone Category: Entertainment Price: $2.99, Version: 1.01 (iTunes) Description: Create - anytime, anywhere. Made by the developers of the award-winning Procreate® for iPad®, Procreate Pocket™ allows... | Read more »
IRON FINGER - Mini Games Championship (...
IRON FINGER - Mini Games Championship 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Quick to play, easy to learn yet hard to master.. TAP, SWIPE & TILT your way through mini games that... | Read more »
Pentaction: Medieval (Games)
Pentaction: Medieval 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Pentaction: Medieval is a turn-based strategy board-game about chance and skill on the battlefield. Take control of your... | Read more »
Hipstify Review
Hipstify Review By Jennifer Allen on December 17th, 2014 Our Rating: :: COOL FILTERSUniversal App - Designed for iPhone and iPad Add filters, quotes, and fancy frames to your images, thanks to Hipstify.   | Read more »

Price Scanner via MacPrices.net

KMI MIDI K-Board Great Gift for Amateur &...
The K-Board is a MIDI Nano keyboard for music creation for iPad, Android, And computers; the easiest way to make music with iPads & Android tablets, and Mac, Windows, or Linux computers. Ultra-... Read more
Amazon offers 15-inch 2.2GHz Retina MacBook P...
 Amazon.com has the 15″ 2.2GHz Retina MacBook Pro on sale for $1699 including free shipping. Their price is $300 off MSRP. Stock is limited, so act now if you’re interested. Read more
Holiday sales continue: MacBook Pros for up t...
 B&H Photo has new MacBook Pros on sale for up to $300 off MSRP as part of their Holiday pricing. Shipping is free, and B&H charges NY sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $1699... Read more
Google Search App For iOS Gets A Major Makeov...
Google has given iOS users an early Christmas present with a substantial update of it’s not-very-often-upgraded Google Search app. Google Search has been my go-to tool for Web searches since it was... Read more
ShopKeep Apple Pay And Chip Card Reader Avail...
ShopKeep, a cloud-based technology provider to more than 10,000 small business owners to manage retail shops and restaurants with iPads, has released its new Apple Pay and chip card reader. This... Read more
Holiday sale! 27-inch 5K iMac for $2299, save...
 B&H Photo has the 27″ 3.5GHz 5K iMac in stock today and on sale for $2299 including free shipping plus NY sales tax only. Their price is $200 off MSRP, and it’s the lowest price available for... Read more
Holiday Sale! 3.7GHz Quad Core Mac Pro availa...
 B&H Photo has the 3.7GHz Quad Core Mac Pro on sale for $2599 including free shipping plus NY sales tax only. Their price is $400 off MSRP, and it’s the lowest price for this model from any... Read more
iPhone 6 Number 3 Canadian Google Search Of 2...
CTVNews.ca reports that Apple’s iPhone 6 was the third highest-trending Google Canada search topic of 2014, exceeded only by Robin Williams largely after his death by suicide in August, and the FIFA... Read more
New iPad mini 3 Counter-Top & Wall Mount...
newMacgadgets has announced new secure all-acrylic displays for the iPad mini 3 (also works fine with the mini 2, last year’s iPad mini With Retina Display, and the original iPad mini). The new iPad... Read more
Holiday sales continue, MacBook Airs for up t...
B&H Photo has 2014 MacBook Airs on sale for up to $120 off MSRP, for a limited time, for the Thanksgiving/Christmas Holiday shopping season. Shipping is free, and B&H charges NY sales tax... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
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
*Apple* Retail - Multiple Positions (US) - A...
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
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions (US) - A...
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
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.