TweetFollow Us on Twitter

Resource Jargon

Volume Number: 13 (1997)
Issue Number: 2
Column Tag: Toolbox Techniques

The Language of Resources

By Chris Stasny

A common sense introduction to the Resource Manager

Say Again?

I discovered a new version of English when I worked the oil fields of Trinidad years ago. Part of this dialect's uniqueness was due to the influence of multiple cultures on the island - notable for its heavy and complex accent. Eventually, I learned how to respond to things like, "And me anudder spanner. Dees one's too slight." (He wanted a larger wrench.)

Some years later I discovered that the Macintosh contained its own rendition of English, where common terms were linked in new ways to form powerful commands. This is clearly demonstrated in Resource Manager calls. Terms like USERESFILE and SETRESATTRS turn out to be everything expected and more. This article will focus on some common resource handling operations. While our syntax will be that of FutureBASIC II, the toolbox calls are so easily recognizable that programmers of all linguistic persuasions should be able to follow along without difficulty.

Resource Files

We all know that our application's resource fork is open and available. Some of us understand that the System's resource file is also open and available. In real life, there are usually between twenty and a hundred resource files open at any given moment, on any given Mac. Remember all of those font files and sound files that you dumped into the System Folder?

The layers of resources are guided strictly by the order they were opened via commands like OPENRESFILE or OPENRFPERM. If you think of your Mac as an oil drum, the System file is thrown into the barrel first and always resides at the bottom. It is followed by a plethora of extensions and additions that come online during startup. We cannot change this order. When we open a resource file, it is always thrown on top. [There are some exceptions. Most notably, CTB tools are loaded below the System resources. -ed.]

Application Heaps

When an application is double-clicked into life, a divider is used to segment the barrel in such a way that the application's resources are isolated from those of other programs. This divider does not extend all the way to the bottom of the drum, where system resources remain pooled and available for all to use. This means that resource files opened by that application can look down upon both application and system resources without ever being aware of items (owned by other applications) on the other side of the divider. This segment of the barrel is known as the application heap.

The search pattern here is important. If we ask the Resource Manager for a chunk of bits, it will respond by searching the top levels of information in our application's quadrant of the barrel. Each failure forces it to submerge deeper into the drum until it eventually finds itself scanning the System resources at the bottom. It is not possible to change this order. At best, we can tell the Resource Manager to start at a deeper level and ignore some of the sludge that has floated to the top. We do this with CALL USERESFILE(resRef).

After USERESFILE, we have effectively chopped off the top portion of the barrel, and items opened after the target file become invisible to the system. This procedure, when improperly used, often sends a program into a death spiral. Our first mistake is to assume that the call somehow changes the order of resource files. This is impossible. Our second mistake is to assume that we can put things right by calling USERESFILE with the application's resource reference number. This is also a fantasy. Here is the only safe way to switch forks in mid stream:

origRes = FN CURRESFILE
CALL USERESFILE(resRef)

‘ Handle your file-specific resource operations here.

CALL USERESFILE(origRes)

Rules to Load By

Let's backtrack for a moment to re-examine the operations involved in opening a resource file. During this operation, the Resource Manager loads a map into memory that lists all of the blocks behind the doors of the newly opened file. If, during creation of that map, the Manager sees something that the programmer marked as "Pre-load," the information is actually moved from the disk into RAM. (The resource can be marked this way either by checking the appropriate box in ResEdit or Resourcerer, or by using SETRESATTRS.)

When we look for a resource with a statement like FN GETRESOURCE, we don't actually dig through RAM searching for our unique block. The Resource Manager scans the maps that are held in memory to see if an entry matches our needs. This entry must be the same resource type with the proper ID or name. Our Manager, clever fellow that he is, does not blindly load a resource when he locates the entry. He first checks to see if the resource has been previously loaded and, if so, returns a handle to the existing item.

Toolbox calls that obtain resource handles are governed by very specific rules. Normally, the resource is moved from disk to memory, but you can circumvent this in cases where you may wish to do something like record and list available resources. The following example records the names of all sound resources without actually loading them into memory.

DIM sndName$(100)

‘ Don't load - just look
CALL SETRESLOAD(_false)

‘ Get res count, but don't let it extend past
‘ the arbitrary limits of the string array.
theCount = FN COUNTRESOURCES(_"snd ")
if theCount > 100 then theCount = 100

‘ Get each resource handle and request 
‘ info on it.
FOR i = 1 TO theCount
 rHndl& = FN GETINDRESOURCE(_"snd ",i)
 CALL GETRESINFO(rHndl&,rID,rType&,rName$)
 sndName$(i) = rName$
NEXT

‘ Restore normal resource loading
CALL SETRESLOAD(_zTrue)

The example used COUNTRESOURCES and GETINDRESOURCE. These calls start at the top of the barrel and continue until they encounter the aging rusty steel at the bottom. (Don't forget, if USERESFILE was invoked, the top of the barrel may have been cut off, and our point of origin for the search may have started lower in the drum than expected.) We could have easily examined the resources that existed in one file to the exclusion of all others by switching to calls that contain "1" in their names. FN COUNT1RESOURCES would return the number of sound resources in the most recently designated file. FN GET1INDRESOURCE would retrieve the indexed resource only in that file.

Let's bring this all together in a routine that searches for sound resources in the System file.

DIM sndName$(100)
origRes = FN CURRESFILE

‘ Ignore anything above the System file.
CALL USERESFILE(0)
CALL SETRESLOAD(_false)

‘ We only want resources in the current file.
theCount = FN COUNT1RESOURCES(_"snd ")
if theCount > 100 then theCount = 100
FOR i = 1 TO theCount

‘ Get indexed resources only from the top file.
 rHndl& = FN GET1INDRESOURCE(_"snd ",i)
 CALL GETRESINFO(rHndl&,rID,rType&,rName$)
 sndName$(i) = rName$
NEXT
CALL SETRESLOAD(_zTrue)

‘ Put things back like we found them.
CALL USERESFILE(origRes)

We have now clearly established the limits of a resource operation. USERESFILE tells us where to start searching, and a "1" in the toolbox name tells us that we should stop after searching a single file. Absence of the "1" forces our search to extend to the deepest recesses of the drum.

Shared Responsibilities

In most cases resources are loaded into memory and used, rather than just being inventoried and listed. The conditions under which these items enter RAM is another perplexing methodology that begs for explanation. The complexity centers around the fact that the management of a resource becomes the shared responsibility of the Resource and Memory Managers.

The Resource Manager begins by examining a resource's attributes to see if it should be purgeable or locked, and allocates the correct memory through FN NEWHANDLE. It can even be loaded into the system heap instead of the application heap, so that it may be shared with other applications that can look downward from their side of the dividers and see it. You may recognize these attributes as check boxes in ResEdit dialogs that are labeled Purgeable, Lock, and System Heap.

Armed with attribute information, the Resource Manager asks the Memory Manager (politely, of course) for a block of memory that is purgeable (or not), locked (or not), or in the system or application heap. Information is moved into that block. This is (practically) the only time resource attributes are examined - when the resource is loaded. From this point forward, the Memory Manager is in charge of the block. Memory Manager calls like HLOCK and HNOPURGE are used to handle the item as it floats around in the heap.

There is one very important exception to this rule. Never use CALL DISPOSEHANDLE on a resource handle. The Memory Manager would carry out its assignment by throwing away the information contained in the handle, but the Resource Manager (who was diligently tracking the block on his own personal tiny clipboard) would be left with a firm grip on an indeterminate chunk of RAM. It's not a pretty sight.

Lock and Purge

To lock or not to lock. That is the question. Most of the time, when I am called upon to debug a particular resource operation, I see abuses that would be too embarrassing to discuss on a daytime talk show. We have a tendency to ignore the attributes set up by the programmer who created the resource in the first place. As with SETRESLOAD and USERESFILE, we need to remain conscious of the creator's intent as we manipulate these items.

Assume that your application has a large preference resource that is loaded at startup. If we lock this piece of information in place, we have locked up a big, otherwise usable piece of binary real estate. Making it non-purgeable would have a similar effect. It may be our intent to move the entire resource into a global record or to examine individual pieces and branch to other operations. Either way, this resource would be marked as purgeable by its creator, but must temporarily be held in memory. We do it like this:

rHndl& = FN GETRESOURCE(_"PREF",_myPrefID)
LONG IF rHndl&

 ‘ Record the status of the handle.
 hState = FN HGETSTATE(rHndl&)

 ‘ Make sure it stays in memory.
 OSErr = FN HNOPURGE(rHndl&)

 ‘ Handle resource operations here,
 ‘ then restore the handle to its original state.
 OSErr = FN HSETSTATE(rHndl&,hState)
END IF

Some toolbox routines handle purging without a programmer's assistance. Picture resources are among the most abused in all of Mac-dom. Take the following (really bad) example.

‘ Bad example! Don't try this at home.

DIM t,l,b,r

rHndl& = FN GETPICTURE(_myPictureID)
OSErr = FN HLOCK(rHndl&)
t;8 = [rHndl&]+_picFrame
CALL OFFSETRECT(t,-l, -t)
CALL DRAWPICTURE(rHndl&,t)
CALL DISPOSEHANDLE(rHndl&)

This example was so wretched that it was painful to type, but it represents the type of resource handling that is common in most programs. The first error was to lock the picture handle. If this picture was to be used often during the course of an application (as might be the case with a tool palette picture), its creator would have marked it as non-purgeable. In most cases, even the purgeable attribute would be turned off so that the picture could be expunged if required. Locking is generally a bad thing and would normally be done only on a temporary basis. (Remember HGETSTATE and HSETSTATE?) In our case, the HLOCK was unnecessary, since QuickDraw manages this particular resource during its operation, and undesirable since low-level picture operations may actually move or resize the picture resource.

Our next major mistake was to assume that the picture was loaded into memory. We immediately went to work on a resource handle without checking it for validity. Then, we disposed of the handle, which was being jointly tracked by the Resource Manager and the Memory Manager. Since DISPOSEHANDLE is a Memory Manager call, the Resource Manager was left out of the operation and is likely to cause serious damage when it next reaches for that resource.

Here's how we should have handled the operation.

  DIM t,l,b,r
 
  rHndl& = FN GETPICTURE(_myPictureID)
  LONG IF rHndl&
   t;8 = [rHndl&]+_picFrame
   CALL OFFSETRECT(t,-l, -t)
   CALL DRAWPICTURE(rHndl&,t)
  END IF

If this was a startup picture, it would probably never be needed again. The moment that the memory it occupied was required for some other operation, the picture would be purged from RAM. On the other hand, if the application's partition was large and the user's requirements small, it might remain in place for the duration.

Later, when the user decided to view the application's "About" box, we would use exactly the same routine to display the picture a second time. If plenty of space was available and the picture had managed to remain in memory, it would not be reloaded. A handle to the existing data would be returned from FN GETPICTURE. If constraints had forced the resource out of memory, it would be reloaded as a result of the call. This debugged example was more memory-efficient, and took fewer lines of code.

Handle Hand-off

While the ownership of resource handles seems to be preordained, we may still exercise control over who will ultimately own the handle. A call to DETACHRESOURCE does this. It pulls the resource's entry from a file's resource map. It does not remove the handle from memory or change the attributes of that handle. After this call, the Memory Manager controls the block, and the Resource Manager ceases to acknowledge its existence. If you wish to dispose of it, you'll have to use DISPOSEHANDLE.

While there is no call that completely releases a Memory Manager handle to the control of the Resource Manager, there is a procedure that turns a handle into a resource: ADDRESOURCE. This call takes a great deal of setup and is best documented in FN pGreplaceRes in the Runtime.INCL file of a Program Generator project. But there are some important rules that deserve attention. When a resource is added, it is added to the current resource file. Use CURRESFILE and USERESFILE to change this during such operations. Adding a resource is a blind operation that allows duplication. If you add a preference resource to your application three times, you'll end up with three copies of the resource in your file.

Slow Execution

Because most folks have a hard time understanding resources, there is a tendency to write out a resource every time it is modified. Apple engineers are no exception. Most of us remember the early days of the Macintosh 840AV. An uninformed ROM rat patched the toolbox call CHANGEDRESOURCE to make it call UPDATERESFILE each time it was called. This was a bad thing. Let me explain why.

When your program calls UPDATERESFILE or WRITERESOURCE, the entire file may be written to disk. Remember that resources are not really magical. They occupy space on a disk, and are ordered according to strict internal guidelines. If you replace a picture that is 50K with one that is 100K, there is no sorcerer's potion that compresses the new resource into the same space used by the old one. The file is simply rewritten, starting at the beginning of the old 50K resource.

When the AV's were first released, folks complained that resource handlers like ResEdit and Program Generator slowed to a crawl. This is because a simple operation (CHANGEDRESOURCE), which was supposed to set a single bit in a single flag, ended up rewriting the file. The reality is that it is almost never necessary to update the file or write its resources. This happens automatically when the file is closed.

There is one additional feature of CHANGEDRESOURCE that deserves attention: You should never call CHANGEDRESOURCE on a purgeable block. When the file is closed, the Resource Manager scans its list to see what has been modified. Then it rewrites the file with these new items in place. If, in the interim, the Memory Manager has purged the block, you will see random data written to the disk. If you have ever seen a file explode from a few hundred K to several megabytes, this is the likely reason. Mark resources in the following manner to prevent this problem.

OSErr = FN HNOPURGE(rHndl&)
CALL CHANGEDRESOURCE(rHndl&)

Conclusion

Our list of rules to live by grows ever more complex. In the olden days, we were just supposed to remember not to tug on Superman's cape or spit into the wind. Now we must watch resource attributes and referee a tenuous cease-fire between two headstrong Macintosh Managers. My friends from Trinidad might beg for simplicity. "And me anudder monager. Dees ones too complex."

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

How to build a successful civilisation i...
GodFinger 2 grants you godlike powers, leaving you to raise a civilization of followers. In the spirit of games like Black & White, the GodFinger games will see you building bigger and better villages, developing more advanced technology and... | Read more »
How to get all the crabs in Mr Crab 2
Mr. Crab 2 may look like a cutesy platformer for kids, but if you're the kind of person who likes to complete a game 100%, you'll soon realise that it's a tougher than a crustacean's shell. [Read more] | Read more »
How to be a star in Britney Spears: Amer...
If you've ever wanted to be a star, baby, then you've probably already checked out Britney Spears: American Dream and are happily making your way up the charts. But fame doesn't come easy, and everyone needs a helping hand sometimes. So we've got... | Read more »
AppSpy is hiring a part time Staff Write...
| Read more »
How to save lives in ER Surgery Simulato...
A serious earthquake has struck a nearby town in ER Surgery Simulator - Emergency Doctor, and it’s up to you to save the victims. [Read more] | Read more »
Tips and tricks to get a high score in G...
Ketchapp Games loves the endless runner genre. And its newest game, Gravity Switch, is no exception. Gravity Switch takes a fresh approach, though, as you move a block, suspended in zero gravity, safely through a maze of shifting pillars. If the... | Read more »
Tips and tricks to get a high score in S...
Smash Fu is a high-paced tile-tapping game that requires quick reflexes and some practice. You’ll have to smash bricks with the skill of a seasoned black belt to get a high score. To raise the stakes a bit, you’ll also have to avoid tapping any... | Read more »
How to keep the ball rolling in Dropple
If you're new to the minimalist puzzler Dropple, you may find yourself struggling to make it beyond the first couple of steps before your ball falls into the endless abyss below. [Read more] | Read more »
Game Craft releases new Legend of War ti...
Set for release at the end of this month, real time strategy title Legend of War seems sure to delight with a veritable feast of sweet features to get stuck into. Developed by Game Craft, the game is due for release through both the App Store and... | Read more »
How not to die in Traffic Rider
Traffic Rider, an Out Run-esque game in which your ride a motorcycle recklessly into trffic, might not seem particularly complicated. [Read more] | Read more »

Price Scanner via MacPrices.net

Apple refurbished iMacs available for up to $...
Apple has 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 available: - 21″ 3.... Read more
Textkraft Professional Becomes A Mobile Produ...
The new update 4.1 of Textkraft Professional for the iPad comes with many new and updated features that will be particularly of interest to self-publishers of e-books. Highlights include import and... Read more
SnipNotes 2.0 – Intelligent note-taking for i...
Indie software developer Felix Lisczyk has announced the release and immediate availability of SnipNotes 2.0, the next major version of his productivity app for iOS devices and Apple Watch.... Read more
Pitch Clock – The Entrepreneur’s Wingman Laun...
Grand Rapids, Michigan based Skunk Tank has announced the release and immediate availability of Pitch Clock – The Entrepreneur’s Wingman 1.1, the company’s new business app available exclusively on... Read more
13-inch 2.9GHz Retina MacBook Pro on sale for...
B&H Photo has the 13″ 2.9GHz Retina MacBook Pro (model #MF841LL/A) on sale for $1599 including free shipping plus NY tax only. Their price is $200 off MSRP. Amazon also has the 13″ 3.9GHz Retina... Read more
Apple price trackers, updated continuously
Scan our Apple Price Trackers for the latest information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the trackers continuously: - 15″... Read more
Clearance 12-inch Retina MacBooks available s...
B&H Photo has dropped prices on leftover 2015 12″ Retina MacBooks with models now available starting at $999. Shipping is free, and B&H charges NY tax only: - 12″ 1.1GHz Gray Retina MacBook... Read more
Check Apple prices on any device with the iTr...
MacPrices is proud to offer readers a free iOS app (iPhones, iPads, & iPod touch) and Android app (Google Play and Amazon App Store) called iTracx, which allows you to glance at today’s lowest... Read more
New 2016 13-inch 256GB MacBook Air on sale fo...
B&H Photo has the new 13″ 1.6GHz/256GB MacBook Air (model MMGG2LL/A) on sale for $1149 including free shipping plus NY sales tax only. Their price is $50 off MSRP. Amazon has the 13″ 1.6GHz/256GB... Read more
Apple refurbished iPad Air 2s available start...
Apple has Certified Refurbished iPad Air 2 available starting at $339. Apple’s one-year warranty is included with each model, and shipping is free: - 128GB Wi-Fi iPad Air 2: $499 - 64GB Wi-Fi iPad... Read more

Jobs Board

*Apple* Nissan Service Technicians - Apple A...
Apple Automotive is one of the fastest growing dealer...and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive , Read more
ISCS *Apple* ID Site Support Engineer - APP...
…position, we are looking for an individual who has experience supporting customers with Apple ID issues and enjoys this area of support. This person should be Read more
Automotive Sales Consultant - Apple Ford Linc...
…you. The best candidates are smart, technologically savvy and are customer focused. Apple Ford Lincoln Apple Valley is different, because: $30,000 annual salary Read more
*Apple* Support Technician II - Worldventure...
…global, fast growing member based travel company, is currently sourcing for an Apple Support Technician II to be based in our Plano headquarters. WorldVentures is Read more
Restaurant Manager (Neighborhood Captain) - A...
…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
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.