TweetFollow Us on Twitter

January 93 - OOPC Memory Management

OOPC Memory Management

Gary Odom

The November 1992 issue of Frameworks had an article by Jeff Alger about memory management in C++ with MacApp. Presented as a contrast to that article, this article describes memory management with OOPC.

Programming with objects involves allocating thousands of blocks. By the time the base classes in OOPC have been initialized, 7000 blocks have been allocated. Within a few minutes of working with a document, 20,000 blocks or more have been allocated. This is typical of object-oriented applications.

Macintosh Memory Management

The top-priority design goal for Macintosh memory management was to fully utilize available memory (space efficiency), even at the expense of other considerations, such as speed efficiency. This was sensible for the original Macintosh, a machine limited to 128 KB, but with relatively large memory demands. The chosen solution was to have relocatable blocks of memory, accessed using pointers to pointers, called handles.

The danger with handles is using them. To access a block, the handle must be dereferenced to its pointer. If the data is accessed a lot in a function, it is more efficient to dereference a handle to its pointer, and repeatedly use the pointer. The pointer is valid as long as the Memory Manager doesn't have a chance to move memory. But if you call any function, you have to know whether that function can move memory. If the function can move memory, you need to dereference the handle to get the pointer again. If memory is moved, the master pointer may change, making the pointer you were using invalid. The problem pointer is called a 'dangling pointer'.

Dangling pointers can be very hard to find, because memory may not move consistently (it depends on how tight memory is at the time). You could be writing into an invalid memory location and not discover a problem until much later. Dangling pointers are a debugging nightmare.

The Macintosh Memory Manager keeps track of every allocated block. This means memory management is optimized for a small number of blocks. With the relocatable block memory scheme, keeping track of a large number of moving blocks imposes significant overhead. This penalty is paid most in trying to allocate non-relocatable (pointer) blocks. To maintain efficient memory use, the Memory Manager always tries to allocate a non-relocatable block toward the bottom or top of the heap, so it won't get in the way during a memory shuffle. Finding space at the edge of the heap while a program is running typically involves a major memory move.

The result is that Memory Manager allocation time per block is distinctly non-linear. While handle allocation drags its tail, the time needed to allocate non-relocatable blocks is atrocious. Chart 1 below illustrates block allocation times in ticks (a tick is 1/60th of a second).

So, the Macintosh Memory Manager optimizes memory usage, but at a significant cost in speed, and with danger lurking in the form of dangling pointers.

OOPC Low-Level Memory Management

OOPC has its own memory manager, using pointers. This avoids the dangling pointer problem caused by using handles. The OOPC memory manager grabs a large chunk of memory from the heap, then slices it up for use. The first chunk is 128 KB. Other chunks are as big as needed, but at least 32 KB. (Chunk sizes are adjustable by an OOPC programmer). Chunks are locked at the top of the heap so they don't get in the way of operating system memory management. Chunks are allocated and freed as needed.

The result is pointer block allocation that does not fragment the heap. Because empty space is managed, not allocated blocks, allocation time is linear. Chart 2 below compares OOPC memory management times to Macintosh Memory Manager times. The times shown are for allocation and deallocation.At 20,000 blocks, OOPC is 20 times faster than Mac OS handles, and 100 times faster than Mac OS pointers.

Low-level memory management is implemented in OOPC using platform-independent functions, such as get_block and free_block. Handle functions (such as get_handle and free_handle) are also supported (using the Mac OS Memory Manager for the Mac version of OOPC). The OS requires handles for resources and some other tasks (such as color pixel maps).

Low-level memory management is only occasionally called directly (by an application programmer). More often, objects are created and released. (Of course, internal methods rely upon low-level memory management.) Let's look at how objects are allocated and deallocated in OOPC.

OOPC Object Memory Management

OOPC object memory management is quite simple. There are six functions/methods involved: new_object (a function), and new, bind, trash, release and empty (all methods).

The new_object function call creates an object, allocating a small amount memory required for all objects (36 bytes), plus any application data the object keeps. new_object calls the new function, which dispatches to an initial data assignment method (the method depends on the class of the object being created). After the new method finishes, an object is fully allocated and initialized.

Some objects need to keep track of other objects. A document object, for example, owns the window object that displays the document. A document object also keeps track of the pages in the document. These links between objects must be maintained.

OOPC's object system has built-in support for maintaining object links. Links between objects are established by calling bind(thisobject, thatobject). By this call, thatobject has created a link (or bond) to thisobject. thisobject cannot be released until thatobject trashes the bond between the objects by calling trash(thisobject, thatobject). Once all links to an object are trashed, the object is released by a trash (or release) call. Using bind and trash functions provides simple garbage collection, preventing objects from being released prematurely (and risking access to 'dead' objects).

release releases an object, but only if there are no links to other objects. When an object is released, empty is called (by release) to deallocate any data allocated in the new method. The release method disposes of the object itself.

Conclusion

Having its own low-level memory management gives a significant speed boost to OOPC-built applications and keeps programming chores simple. At the high level, built-in support for object linking provides garbage collection and safety with object access.
 
AAPL
$524.76
Apple Inc.
+5.75
MSFT
$40.05
Microsoft Corpora
-0.35
GOOG
$539.30
Google Inc.
-17.24

MacTech Search:
Community Search:

Software Updates via MacUpdate

PDFpenPro 6.2 - Advanced PDF toolkit for...
PDFpenPro allows users to edit PDF's easily. Add text, images and signatures. Fill out PDF forms. Merge or split PDF documents. Reorder and delete pages. Even correct text and edit graphics! Create... Read more
PDFpen 6.2 - Edit and annotate PDFs with...
PDFpen allows users to easily edit PDF's. Add text, images and signatures. Fill out PDF forms. Merge or split PDF documents. Reorder and delete pages. Even correct text and edit graphics! Features... Read more
Monolingual 1.5.9 - Remove unwanted OS X...
Monolingual is a program for removing unnecesary language resources from OS X, in order to reclaim several hundred megabytes of disk space. It requires a 64-bit capable Intel-based Mac and at least... Read more
Maya 2015 - Professional 3D modeling and...
Maya is an award-winning software and powerful, integrated 3D modeling, animation, visual effects, and rendering solution. Because Maya is based on an open architecture, all your work can be scripted... Read more
Starcraft II: Wings of Liberty 1.1.1.180...
Download the patch by launching the Starcraft II game and downloading it through the Battle.net connection within the app. Starcraft II: Wings of Liberty is a strategy game played in real-time. You... Read more
Sibelius 7.5.0 - Music notation solution...
Sibelius is the world's best-selling music notation software for Mac. It is as intuitive to use as a pen, yet so powerful that it does most things in less than the blink of an eye. The demo includes... Read more
Typinator 5.9 - 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
MYStuff Pro 2.0.16 - Create inventories...
MYStuff Pro is the most flexible way to create detail-rich inventories for your home or small business. Add items to MYStuff by dragging and dropping existing information, uploading new images, or... Read more
TurboTax 2013.r17.002 - Manage your 2013...
TurboTax guides you through your tax return step by step, does all the calculations, and checks your return for errors and overlooked deductions. It lets you file your return electronically to get... Read more
TrailRunner 3.8.769 - Route planning for...
Note: While the software is classified as freeware, it is actually donationware. Please consider making a donation to help support development. TrailRunner is the perfect companion for runners,... Read more

Latest Forum Discussions

See All

Call of Cookie Review
Call of Cookie Review By Jordan Minor on April 17th, 2014 Our Rating: :: COOKIE CRUMBLESUniversal App - Designed for iPhone and iPad Call of Cookie proves that plants aren’t the only fighting foods out there.   | Read more »
Corel Launches Video Editing App Pinnacl...
Corel Launches Video Editing App Pinnacle Studio for iPhone, Updates iPad Version for iOS 7 Posted by Tre Lawrence on April 17th, 2014 [ | Read more »
Bad Vamp Review
Bad Vamp Review By Jennifer Allen on April 17th, 2014 Our Rating: :: BASIC VAMPIRIC ADVENTURESUniversal App - Designed for iPhone and iPad Run or destroy the vampires in this simple, single-screen game that lacks real bite.   | Read more »
The Shadow Sun gets a New Update, Goes o...
The Shadow Sun gets a New Update, Goes on Sale for the First Time Since its Release Posted by Tre Lawrence on April 17th, 2014 [ permalink ] | Read more »
Bullet Pea Review
Bullet Pea Review By Jordan Minor on April 17th, 2014 Our Rating: :: PEA SHOOTERUniversal App - Designed for iPhone and iPad Bullet Pea’s “jumps only” gameplay is novel in theory, but has problems in practice.   | Read more »
iOOTP Baseball 2014 Edition (Games)
iOOTP Baseball 2014 Edition 1.0.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.0 (iTunes) Description: Guide your favorite baseball team to glory! Out of the Park Baseball, the most realistic and best-selling... | Read more »
Real Racing 3 gets a New Update that Add...
Real Racing 3 gets a New Update that Adds in Open Wheel Racing Experience and More Posted by Tre Lawrence on April 17th, 2014 [ permalink ] | Read more »
Runtastic PRO Review
Runtastic PRO Review By Jennifer Allen on April 17th, 2014 Our Rating: :: COOL RUNNINGSiPhone App - Designed for the iPhone, compatible with the iPad Keep track of your runs, cycles, and more with this feature-rich exercise app.   | Read more »
Download pickWEB and Access a Thematic C...
Download pickWEB and Access a Thematic Catalogue of the World’s Most Interesting Websites [Sponsored] Posted by Simon Reed on April 17th, 2014 [ | Read more »
Unpossible (Games)
Unpossible 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: **Important** Requires at least iPad 2, iPhone 4S, iPod Touch (5th gen), or newer. | Read more »

Price Scanner via MacPrices.net

Updated iPads Coming Sooner Than We Had Thoug...
MacRumors, cites KGI securities analyst Ming Chi Kuo, well-respected as an Apple product prognisticator, saying that Apple will introduce an upgraded iPad Air and iPad mini in 2014/Q3, meaning the... Read more
Toshiba Unveils New High And Low End Laptop M...
Toshiba has announced new laptop models covering both the high-end and low-end of the notebook computer spectrum. Toshiba 4K Ultra HD Laptop Toshiba’s new Satellite P55t features one of the world’s... Read more
Save up to $270 with Apple refurbished 13-inc...
The Apple Store has Apple Certified Refurbished October 2013 13″ Retina MacBook Pros available starting at $1099, with models up to $270 off MSRP. Apple’s one-year warranty is standard, and shipping... Read more
Apple now offering refurbished iPad mini with...
The Apple Store has Certified Refurbished 2nd generation iPad minis with Retina Displays now available starting at $339. Apple’s one-year warranty is included with each model, and shipping is free.... Read more
Microsoft Blinks – Drops Microsoft Office 365...
Microsoft has dropped the annual subscription fee for Microsoft Office 365 Personal – which is needed in order to create and edit documents in Microsoft Office for iPad. However, Apple’s iOS and OS X... Read more
New AVG Vault Apps for iOS and Android Help K...
AVG Technologies N.V. an online security company for 177 million active users, has announced the launch of its latest mobile application, AVG Vault. The free app introduces an innovative user... Read more
Free Local Carrot iPhone App Helps Find Fresh...
I love fresh vegetables. I’m not a vegan, although I was for several years in the 1980s, but fresh vegetables and other whole foods are still my dietary mainstays as a matter of taste rather than... Read more
CarSO Pro – Car Service and Finance Manager/O...
Lviv, Ukraine-based BM-Studios’ CarSO Pro is a tool to manage operations concerning your car. Never forget to change the oil or prolong the insurance for your car. Remember when you’ve done the car... Read more
Apple refurbished iPad Airs available startin...
Apple is now offering Certified Refurbished iPad Airs for up to $140 off MSRP. Apple’s one-year warranty is included with each model, and shipping is free. The following Airs are available today: -... Read more
21-inch 2.7GHz iMac on sale for $1179, save $...
B&H Photo has the 21″ 2.7GHz iMac on sale for $1179 including free shipping plus NY sales tax only. Their price is $120 off MSRP. Add an iMac to your shopping cart, and B&H will offer an... Read more

Jobs Board

*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Retail - Manager - Holyoke - Apple I...
Job Summary Keeping an Apple Store thriving requires a diverse set of leadership skills, and as a Manager, you’re a master of them all. In the store’s fast-paced, Read more
*Apple* Retail - Manager - Apple (United Sta...
Job SummaryKeeping an Apple Store thriving requires a diverse set of leadership skills, and as a Manager, you're a master of them all. In the store's fast-paced, dynamic Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Retail - Market Leader - Cincinnati...
…challenges of developing individuals, building teams, and affecting growth across Apple Stores. You demonstrate successful leadership ability - focusing on excellence Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.