TweetFollow Us on Twitter

Winter 92 - BE OUR GUEST

BE OUR GUEST

BACKGROUND-ONLY APPLICATIONS IN SYSTEM 7

C. K. HAUN


One of the least heralded new features of System 7, but nonetheless a very important one, is full support for faceless background applications (FBAs). An FBA is a full-fledged application that's invisible to the user. It has its own event loop, and it receives time and some events like any other application, but it doesn't have a menu bar, windows, dialogs, or other graphic components. An FBA is a normal file of type 'APPL'.

FBAs are, by a stretch of the imagination, similar to UNIX® daemons. The purpose of an FBA is to provide services to other applications or to monitor the system. For instance, an application that periodically checks your hard drive for files that haven't been backed up lately is a perfect candidate for FBA status. Thus, an FBA can be a silent partner to your application, INIT, cdev, desk accessory, or driver.

An FBA is the best way to provide certain services. For example, an FBA paired with a desk accessory can enable the DA to send Apple events, something a DA cannot usually do. (See the AECDEV/AEDAEMON sample in the snippets provided with the DTS Sample Code on theDeveloper CD Series disc.) An FBA can replace an INIT that patches traps to get time and provides services, or it can replace a driver that depended on periodic run messages to operate. Converting to an FBA not only frees you from having to patch to get the time you need, but also gives you a fully supported and documented interface and design. You get all the advantages of a full application, without the overhead of a user interface.

An FBA can also be an application manager for a suite of applications. With an FBA, you can control the launching of and communication between applications, using LaunchApplication and Apple events.

Writing an FBA is simple. An FBA is a subset of a standard Macintosh application, consisting of a minimal event loop and the code to handle two types of events, null events and high-level events. No other events are sent to an FBA. This makes a great deal of sense, since every other event (keystroke, mouse click, and such) is designed for foreground applications.

The SmallDaemon backgrounder shell included on theDeveloper CD Series disc shows just how simple the basics of an FBA are:

Boolean         gQuit = false;
EventRecord     gERecord;
unsigned long   gMySleep = 50000; /* A long, long time */
main()
{
    /* Routine for installing my Apple event handlers. 
       Need to install the four required
       handlers, plus handlers for any other events
       I want to accept. */
    InitAEStuff();
    while (gQuit == false) {
        /* A normal call to WaitNextEvent. I want
           only highLevelEvents, since all other
           events relate to interface actions, and I
           have no interface. */
        if (WaitNextEvent(highLevelEventMask, &gERecord, gMySleep,
               0)) {
            /* I'll get only null and high-level events. */
            switch (gERecord.what) {
            case nullEvent:
            /* No null processing in this sample. */
            break;
            
            case kHighLevelEvent:
            /* Get a high-level event (an Apple event) and process */
            /* it. */
            DoHighLevel(&gERecord);
            break;
            }
        }
    }
}

As you can see, there's not much there. The first thing you'll notice is that an FBA doesn't start up any managers. All the managers you normally start are based on user interface actions. Thus, they should not  be called in an FBA--in fact, calling them will cause your FBA to crash. There's one exception to this rule: you can initialize QuickDraw, butonly to provide yourself with off-screen grafPorts or to use some QuickDraw functions. Do not do any actual screen drawing from an FBA.

You'll also notice that you don't pass a mouse region to WaitNextEvent. That's obvious, since you're never in the foreground and have no windows or mouse control to track. And the only events you'll be handling are null events and high-level events (Apple events).

The next step is to make sure the system knows that you're a background-only application. You do this with a SIZE resource, by setting the canBackground and onlyBackground bits to true. When the Finder launches your FBA, it checks these bits and finds that you're a background-only application.

Some tips and techniques to keep in mind:

  • Always remember that an FBA is invisible to the user. An FBA doesnot  show up in the Process menu or in the Finder About window. Also, its heap memory is added to the system size thermometer bar in the Finder About window, even though it has its own application heap. The user often will have no idea that it's running, so be friendly.
  • Being friendly means yielding time. Have a very large sleep time when you're not actually doing some processing. If you don't, users will think that their machine has slowed down inexplicably. You can always use the new Process Manager call WakeUpProcess to get yourself back into fast processing when you need to.
  • Being friendly also means making sure you're occupying thesmallest  heap size you can possibly run in. Again, users may never know that your FBA exists, so if you eat up a bunch of memory in your FBA, users will not understand why they've lost so much memory. Be conservative.
  • Putting your FBA in the Startup Items folder in the System Folder is also a good idea. That will ensure that your FBA is launched right after Finder startup and will put the FBA high in the Process Manager's heap, preventing fragmentation of application memory space.
  • Use WakeUpProcess to get your FBA running. Keep your sleep time at maximum normally, and when you need to start doing null processing (in response to an Apple event or PPC completion routine, for example) use the Process Manager to wake yourself up. WakeUpProcess can be called at interrupt time. Then, when you've finished processing, drop back to a maximum sleep time.

For further information and help with writing an FBA, refer to the Process Manager chapter ofInside Macintosh Volume VI. Then try it--you'll like it!

C. K. HAUN has been programming Apple computers since 1979, writing commercial education, utility, and game applications for the Apple II, IIGS, and Macintosh, with some occasional dark forays into the Big Blue world. (It paid the rent.) He currently works in Developer Technical Support and focuses mainly on Apple events and the Edition Manager. Besides working to provide the best possible support to developers, he's been trying to organize the Silicon Valley chapter of Heck's Moofers, a motorcycle club devoted to the precept that computer nerds on bikes can raise heck too, darn it. And yes, that really is  his mustache.*

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Navicat Premium Essentials 12.1.25 - Pro...
Navicat Premium Essentials is a compact version of Navicat which provides basic and necessary features you will need to perform simple administration on a database. It supports the latest features... Read more
Sketch 58 - Design app for UX/UI for iOS...
Sketch is an innovative and fresh look at vector drawing. Its intentionally minimalist design is based upon a drawing space of unlimited size and layers, free of palettes, panels, menus, windows, and... Read more
ClipGrab 3.8.5 - Download videos from Yo...
ClipGrab is a free downloader and converter for YouTube, Vimeo, Facebook and many other online video sites. It converts downloaded videos to MPEG4, MP3 or other formats in just one easy step Version... Read more
Dash 4.6.6 - Instant search and offline...
Dash is an API documentation browser and code snippet manager. Dash helps you store snippets of code, as well as instantly search and browse documentation for almost any API you might use (for a full... Read more
FotoMagico 5.6.8 - Powerful slideshow cr...
FotoMagico lets you create professional slideshows from your photos and music with just a few, simple mouse clicks. It sports a very clean and intuitive yet powerful user interface. High image... Read more
Civilization VI 1.2.4 - Next iteration o...
Sid Meier’s Civilization VI is the next entry in the popular Civilization franchise. Originally created by legendary game designer Sid Meier, Civilization is a strategy game in which you attempt to... Read more
Skype 8.52.0.138 - Voice-over-internet p...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
Bookends 13.2.6 - Reference management a...
Bookends is a full-featured bibliography/reference and information-management system for students and professionals. Bookends uses the cloud to sync reference libraries on all the Macs you use.... Read more
BusyContacts 1.4.0 - Fast, efficient con...
BusyContacts is a contact manager for OS X that makes creating, finding, and managing contacts faster and more efficient. It brings to contact management the same power, flexibility, and sharing... Read more
Chromium 77.0.3865.75 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. Version 77.0.3865.75: A list of changes is available... Read more

Latest Forum Discussions

See All

Yoozoo Games launches Saint Seiya Awaken...
If you’re into your anime, you’ve probably seen or heard of Saint Seiya. Based on a shonen manga by Masami Kurumada, the series was massively popular in the 1980s – especially in its native Japan. Since then, it’s grown into a franchise of all... | Read more »
Five Nights at Freddy's AR: Special...
Five Nights at Freddy's AR: Special Delivery is a terrifying new nightmare from developer Illumix. Last week, FNAF fans were sent into a frenzy by a short teaser for what we now know to be Special Delivery. Those in the comments were quick to... | Read more »
Rush Rally 3's new live events are...
Last week, Rush Rally 3 got updated with live events, and it’s one of the best things to happen to racing games on mobile. Prior to this update, the game already had multiplayer, but live events are more convenient in the sense that it’s somewhat... | Read more »
Why your free-to-play racer sucks
It’s been this way for a while now, but playing Hot Wheels Infinite Loop really highlights a big issue with free-to-play mobile racing games: They suck. It doesn’t matter if you’re trying going for realism, cart racing, or arcade nonsense, they’re... | Read more »
Steam Link Spotlight - The Banner Saga 3
Steam Link Spotlight is a new feature where we take a look at PC games that play exceptionally well using the Steam Link app. Our last entry talked about Terry Cavanaugh’s incredible Dicey Dungeons. Read about how it’s a great mobile experience... | Read more »
PSA: GRIS has some issues
You may or may not have seen that Devolver Digital just released GRIS on the App Store, but we wanted to do a quick public service announcement to say that you might not want to hop on buying it just yet. The puzzle platformer has come to small... | Read more »
Combo Quest (Games)
Combo Quest 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Combo Quest is an epic, time tap role-playing adventure. In this unique masterpiece, you are a knight on a heroic quest to retrieve... | Read more »
Hero Emblems (Games)
Hero Emblems 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: ** 25% OFF for a limited time to celebrate the release ** ** Note for iPhone 6 user: If it doesn't run fullscreen on your device... | Read more »
Puzzle Blitz (Games)
Puzzle Blitz 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Puzzle Blitz is a frantic puzzle solving race against the clock! Solve as many puzzles as you can, before time runs out! You have... | Read more »
Sky Patrol (Games)
Sky Patrol 1.0.1 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0.1 (iTunes) Description: 'Strategic Twist On The Classic Shooter Genre' - Indie Game Mag... | Read more »

Price Scanner via MacPrices.net

Preorder your Apple Watch Series 5 today at A...
Amazon has Apple Watch Series 5 GPS models available for preorder and on sale today for $15 off Apple’s MSRP. Shipping is free and starts on September 20th: – 40mm Apple Watch Series 5 GPS: $384.99 $... Read more
21″ iMacs on sale for $100 off Apple’s MSRP,...
B&H Photo has new 21″ Apple iMacs on sale for $100 off MSRP with models available starting at $999. These are the same iMacs offered by Apple in their retail and online stores. Overnight shipping... Read more
2018 4 and 6-Core Mac minis on sale today for...
Apple resellers are offering new 2018 4-Core and 6-Core Mac minis for $100-$150 off MSRP for a limited time. B&H Photo has the new 2018 4-Core and 6-Core Mac minis on sale for up to $150 off... Read more
Save $150-$250 on 10.2″ WiFi + Cellular iPads...
Verizon is offering $150-$250 discounts on Apple’s new 10.2″ WiFi + Cellular iPad with service. Buy the iPad itself and save $150. Save $250 on the purchase of an iPad along with an iPhone. The fine... Read more
Apple continues to offer 13″ 2.3GHz Dual-Core...
Apple has Certified Refurbished 2017 13″ 2.3GHz Dual-Core non-Touch Bar MacBook Pros available starting at $1019. An standard Apple one-year warranty is included with each model, outer cases are new... Read more
Apple restocks 2018 MacBook Airs, Certified R...
Apple has restocked Certified Refurbished 2018 13″ MacBook Airs starting at only $849. Each MacBook features a new outer case, comes with a standard Apple one-year warranty, and is shipped free. The... Read more
Sunday Sale! 2019 27″ 5K 6-Core iMacs for $20...
B&H Photo has the new 2019 27″ 5K 6-Core iMacs on stock today and on sale for up to $250 off Apple’s MSRP. Overnight shipping is free to many locations in the US. These are the same iMacs sold by... Read more
Weekend Sale! 2019 13″ MacBook Airs for $200...
Amazon has new 2019 13″ MacBook Airs on sale for $200 off Apple’s MSRP, with prices starting at $899, each including free shipping. Be sure to select Amazon as the seller during checkout, rather than... Read more
2019 15″ MacBook Pros now on sale for $350-$4...
B&H Photo has Apple’s 2019 15″ 6-Core and 8-Core MacBook Pros on sale today for $350-$400 off MSRP, starting at $2049, with free overnight shipping available to many addresses in the US: – 2019... Read more
Buy one Apple Watch Series 5 at Verizon, get...
Buy one Apple Watch Series 5 at Verizon, and get a second Watch for 50% off. Plus save $10 on your first month of service. The fine print: “Buy Apple Watch, get another up to 50% off on us. Plus $10... Read more

Jobs Board

*Apple* Mobility Pro-Store 149 - Best Buy (U...
**731985BR** **Job Title:** Apple Mobility Pro-Store 149 **Job Category:** Store Associates **Location Number:** 000149-Towson-Store **Job Description:** At Best Read more
Student Employment (Blue *Apple* Cafe) Spri...
Student Employment (Blue Apple Cafe) Spring 2019 Penn State University Campus/Location: Penn State Brandywine Campus City: Media, PA Date Announced: 12/20/2018 Date Read more
Windows/ *Apple* Technical Support Engineer...
Windows/ Apple Technical Support Engineer McLean , VA , US Apply + Be you + Be Booz Allen + Be empowered + Learn More Job Description Location: McLean, VA, US Job Read more
*Apple* Mobile Master - Best Buy (United Sta...
**725617BR** **Job Title:** Apple Mobile Master **Job Category:** Store Associates **Location Number:** 001095-Chesterfield-Store **Job Description:** **What does a Read more
Geek Squad *Apple* Master Consultation Agen...
**732415BR** **Job Title:** Geek Squad Apple Master Consultation Agent **Job Category:** Services/Installation/Repair **Location Number:** 000425-Hickory-Store **Job Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.