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

Latest Forum Discussions

See All

Six fantastic ways to spend National Vid...
As if anyone needed an excuse to play games today, I am about to give you one: it is National Video Games Day. A day for us to play games, like we no doubt do every day. Let’s not look a gift horse in the mouth. Instead, feast your eyes on this... | Read more »
Old School RuneScape players turn out in...
The sheer leap in technological advancements in our lifetime has been mind-blowing. We went from Commodore 64s to VR glasses in what feels like a heartbeat, but more importantly, the internet. It can be a dark mess, but it also brought hundreds of... | Read more »
Today's Best Mobile Game Discounts...
Every day, we pick out a curated list of the best mobile discounts on the App Store and post them here. This list won't be comprehensive, but it every game on it is recommended. Feel free to check out the coverage we did on them in the links below... | Read more »
Nintendo and The Pokémon Company's...
Unless you have been living under a rock, you know that Nintendo has been locked in an epic battle with Pocketpair, creator of the obvious Pokémon rip-off Palworld. Nintendo often resorts to legal retaliation at the drop of a hat, but it seems this... | Read more »
Apple exclusive mobile games don’t make...
If you are a gamer on phones, no doubt you have been as distressed as I am on one huge sticking point: exclusivity. For years, Xbox and PlayStation have done battle, and before this was the Sega Genesis and the Nintendo NES. On console, it makes... | Read more »
Regionally exclusive events make no sens...
Last week, over on our sister site AppSpy, I babbled excitedly about the Pokémon GO Safari Days event. You can get nine Eevees with an explorer hat per day. Or, can you? Specifically, you, reader. Do you have the time or funds to possibly fly for... | Read more »
As Jon Bellamy defends his choice to can...
Back in March, Jagex announced the appointment of a new CEO, Jon Bellamy. Mr Bellamy then decided to almost immediately paint a huge target on his back by cancelling the Runescapes Pride event. This led to widespread condemnation about his perceived... | Read more »
Marvel Contest of Champions adds two mor...
When I saw the latest two Marvel Contest of Champions characters, I scoffed. Mr Knight and Silver Samurai, thought I, they are running out of good choices. Then I realised no, I was being far too cynical. This is one of the things that games do best... | Read more »
Grass is green, and water is wet: Pokémo...
It must be a day that ends in Y, because Pokémon Trading Card Game Pocket has kicked off its Zoroark Drop Event. Here you can get a promo version of another card, and look forward to the next Wonder Pick Event and the next Mass Outbreak that will be... | Read more »
Enter the Gungeon review
It took me a minute to get around to reviewing this game for a couple of very good reasons. The first is that Enter the Gungeon's style of roguelike bullet-hell action is teetering on the edge of being straight-up malicious, which made getting... | Read more »

Price Scanner via MacPrices.net

Take $150 off every Apple 11-inch M3 iPad Air
Amazon is offering a $150 discount on 11-inch M3 WiFi iPad Airs right now. Shipping is free: – 11″ 128GB M3 WiFi iPad Air: $449, $150 off – 11″ 256GB M3 WiFi iPad Air: $549, $150 off – 11″ 512GB M3... Read more
Apple iPad minis back on sale for $100 off MS...
Amazon is offering $100 discounts (up to 20% off) on Apple’s newest 2024 WiFi iPad minis, each with free shipping. These are the lowest prices available for new minis among the Apple retailers we... Read more
Apple’s 16-inch M4 Max MacBook Pros are on sa...
Amazon has 16-inch M4 Max MacBook Pros (Silver and Black colors) on sale for up to $410 off Apple’s MSRP right now. Shipping is free. Be sure to select Amazon as the seller, rather than a third-party... Read more
Red Pocket Mobile is offering a $150 rebate o...
Red Pocket Mobile has new Apple iPhone 17’s on sale for $150 off MSRP when you switch and open up a new line of service. Red Pocket Mobile is a nationwide MVNO using all the major wireless carrier... Read more
Switch to Verizon, and get any iPhone 16 for...
With yesterday’s introduction of the new iPhone 17 models, Verizon responded by running “on us” promos across much of the iPhone 16 lineup: iPhone 16 and 16 Plus show as $0/mo for 36 months with bill... Read more
Here is a summary of the new features in Appl...
Apple’s September 2025 event introduced major updates across its most popular product lines, focusing on health, performance, and design breakthroughs. The AirPods Pro 3 now feature best-in-class... Read more
Apple’s Smartphone Lineup Could Use A Touch o...
COMMENTARY – Whatever happened to the old adage, “less is more”? Apple’s smartphone lineup. — which is due for its annual refresh either this month or next (possibly at an Apple Event on September 9... Read more
Take $50 off every 11th-generation A16 WiFi i...
Amazon has Apple’s 11th-generation A16 WiFi iPads in stock on sale for $50 off MSRP right now. Shipping is free: – 11″ 11th-generation 128GB WiFi iPads: $299 $50 off MSRP – 11″ 11th-generation 256GB... Read more
Sunday Sale: 14-inch M4 MacBook Pros for up t...
Don’t pay full price! Amazon has Apple’s 14-inch M4 MacBook Pros (Silver and Black colors) on sale for up to $220 off MSRP right now. Shipping is free. Be sure to select Amazon as the seller, rather... Read more
Mac mini with M4 Pro CPU back on sale for $12...
B&H Photo has Apple’s Mac mini with the M4 Pro CPU back on sale for $1259, $140 off MSRP. B&H offers free 1-2 day shipping to most US addresses: – Mac mini M4 Pro CPU (24GB/512GB): $1259, $... Read more

Jobs Board

All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.