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Process Manager Q&As


This Technical Note contains a collection of archived Q&As relating to a specific topic - questions sent the Developer Support Center (DSC) along with answers from the DSC engineers. Current Q&As can be found on the Macintosh Technical Q&As web site.

[Oct 01 1990]

LaunchApplication and canBackground bit

Date Written: 3/26/93

Last reviewed: 6/24/93

When I use LaunchApplication with the launchDontSwitch bit set in the launchControlFlags field for an application that doesn't have the canBackground size resource bit set, LaunchApplication returns 0 (noErr) but the application doesn't launch. What gives?

LaunchApplication doesn't return an error in this case because the application actually is launched. But, since it doesn't have the canBackground bit set, and it was launched into the background, it never gets any processor time, which means that it doesn't initialize anything and isn't added to the process menu. If you double click an application that's been launched like this, it will bounce forward and get processor time, initialize itself and be added to the process menu as usual.

You can verify this by using an application that lists current processes, to see whether the application is indeed listed as running, but it will never get time unless it's manually brought forward by the user.

We've entered this as a bug in our database. Hopefully we'll be able to address it in the future.

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Process Manager and ResErrProc

Date Written: 3/30/93

Last reviewed: 7/2/93

I've installed a resource error procedure (ResErrProc) but it gets called with an error -192 (resNotFound) every time I release a resource. Why is this happening and what can I do to fix it?

If you install a ResErrProc, the Process Manager switches it out when switching to another application. The problem you're having is that the Process Manager doesn't switch it out while in Process Manager code itself. If you break into the debugger in your ResErrProc and examine register A5, you'll find it's not your A5; it is in fact the Process Manager's.

What has happened is that the Process Manager has patched ReleaseResource for its own mysterious purposes. An error occurs, which the Process Manager believes it can ignore, but because your ResErrProc is still installed, it gets called and reports the error. To avoid this, when your ResErrProc gets called, check to see whether register A5 is equal to the low-memory global CurrentA5. If the values aren't equal, you can assume your application wasn't responsible for the error, so you can ignore it. The code might look like this:

void MyResErrorProc (void)
    long    A5;
    A5 = SetCurrentA5 ();
    if (A5 == *(long *)CurrentA5)  /* If they're equal, we're in current app code */
        Debugger();                /* ...or whatever you want to do here */
    else                           /* Not in current app code */
        SetA5 (A5);                /* Restore old A5 */

Similar problems can occur if you make calls that make other Resource Manager calls. The secondary calls may produce errors that are inconsequential to the primary call, but your ResErrProc gets called anyway. This makes ResErrProcs of limited use, so use any information reported by a ResErrProc carefully.

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How to keep Process Manager from closing files when app quits

Date Written: 8/24/92

Last reviewed: 6/14/93

Somehow System 7 keeps track of which application opened a file, so that it can close files left open if the application crashes. Well, I need to defeat this mechanism to keep the Macintosh Operating System from closing a file after a user quits our application. How do I do that?

The Process Manager keeps track of the files opened by an application. Since applications are normally supposed to close the files they open, but many don't, Apple decided to let the Process Manager do the job for those that don't do it themselves. You aren't the first to complain about this behavior since there are several valid cases for leaving a file open. Anyway, there are two ways to work around this.

If this first method will work for you, you should use it since it doesn't involve patching anything. Let your application launch a small faceless background application (FBA) whose purpose is to open files for you. Communicate with the FBA through Apple events to:

  • tell it what files to open for you and have it return the file reference number (or any errors).
  • tell it what files to close for you.
  • ask it what files are open.
  • tell it to quit.

Use MaxLongInt for the FBA's sleep value passed to WaitNextEvent so it won't use any system time until you ask it to do something - it'll wake up when it receives an Apple event. Your application can find out if the FBA is already running (and get its process serial number for the address of Apple events) by looking for the FBA with the Process Manager's GetProcessInformation function.

An FBA is the recommended method. The other method is to patch _Close with an INIT to keep the Process Manager from closing certain files.

A couple of examples that might help you with the FBA can be found on the Developer CD. They're called AEDaemon and AEInteraction Sample.

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How to tell if Macintosh Process Manager is present

Date Written: 1/21/91

Last reviewed: 6/14/93

What is the proper way to tell if the Process Manager is present?

The System 7 Process Manager is available if a Gestalt call with the selector gestaltOSAttr returns noErr and the gestaltLaunchControl bit is set in the response. This is documented on page 29-17 of Inside Macintosh Volume VI.

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Code snippet to check for high-level event support in a process

Date Written: 11/12/90

Last reviewed: 6/14/93

How can I find out if a specific process is running on my system and if it supports high-level System 7 events?

You can check to see if a specific process supports high-level events with code similar to this:

Program Test;


  err: OSErr;
  myPSN: ProcessSerialNumber;
  myPInfoRec: ProcessInfoRec;
  myPName: Str255;
  myProcessSignature: OSType;

  myPSN.highLongOfPSN := 0; { start at beginning of process list }
  myPSN.lowLongOfPSN := kNoProcess;

  myPInfoRec.processInfoLength := sizeOf(ProcessInfoRec);
  myPInfoRec.processName := @myPName;
  myPInfoRec.processAppSpec := NIL;

  myProcessSignature := 'MACS'; { looking for the Finder's signature }

  WHILE (GetNextProcess(myPSN) = noErr) DO
    IF GetProcessInformation(myPSN, myPInfoRec) = noErr
        IF (myPInfoRec.processSignature = myProcessSignature) AND
          (BAND(myPInfoRec.processMode, modeHighLevelEventAware) <> 0)
              Writeln(myPInfoRec.processName^, ' is high level event aware.');

Launching a Macintosh application

Date Written: 4/30/91

Last reviewed: 6/14/93

Under MultiFinder or Macintosh System 7, is there a way to set a flag to terminate the current application before launching a different application? Under standard Finder, the launcher quits before the launchee starts. However, under MultiFinder or System 7, they both must stay in memory for a brief time until control returns to the launcher and it hits the ExitToShell. Because most of our programs are set to use 1 MB, we need 2 MB of memory available for a short time.

Two distinct cases are involved here: the System 7.0 case and the pre-System 7.0 case.

In System 7.0 there is a new way to launch applications. The function is called (appropriately enough) LaunchApplication. The function and its new extended parameter block are documented in the Process Management chapter of Inside Macintosh Volume VI.

You can determine whether your system software has the new Launch Control capabilities by using Gestalt:

OSErr myOSErr;
long response;

myOSErr = Gestalt(gestaltOSAttr, &response);
if (noErr != myOSErr)   /* If an OSErr occurs we must be pre-System 7.0 */
  /* Handle pre-System 7.0 case */
if BTst(response, gestaltLaunchFullFileSpec)
  /* Handle System 7.0 case */
  /* Handle pre-System 7.0 case */

The above code assumes that you are developing with interfaces and libraries based on MPW 3.2, as those interfaces and libraries support Gestalt even on system software versions that don't implement the Gestalt trap.

The portion of the Process Management chapter of Inside Macintosh Volume VI that will interest you is the description of the launchControlFlags field of the parameter block. Here's what the Process Management chapter has to say:

"When you use the LaunchApplication function, you specify the launch options in the launchControlFlags field of the launch parameter block. These are the constants you can specify in the launchControlFlags field.

  launchContinue = $4000;
  launchNoFileFlags = $0800;
  launchUseMinimum = $0400;
  launchDontSwitch = $0200;
  launchAllow24Bit = $0100;
  launchInhibitDaemon = $0080;

Set the launchContinue flag if you want your application to continue after the specified application is launched. If you do not set this flag, LaunchApplication terminates your application after launching the specified application, even if the launch fails."

In other words, you have to request that your launching application continue if you use LaunchApplication - the default is to do precisely what you want. Note that clearing the launchContinue flag is effectively the same as following the LaunchApplication call with an ExitToShell call. Because applications should not terminate within an Apple event handler, they must set the launchContinue flag when calling LaunchApplication from within an Apple event handler.

This leaves the pre-System 7.0 case. System 4.1 and later versions allow for the use of an extended Launch parameter block also, but it is somewhat different from that of System 7.0. The complete details can be found in the Macintosh Technical Note "Sub(Launching) From a High-Level Language." You'll need to use the extended version of the parameter block and specify a launch rather than a sublaunch.

Unfortunately, the launching application does in fact not quit until the launchee has come up. It sounds like you will have to launch a tiny utility application that then turns around and launches your real target.

A good example of how all of this works in the System 7.0 case can be found in the ProcDoggie 1.0a6 sample code, which is in the Sample Code folder on the System 7.0 February 1991 beta CD-ROM. Among other things, it demonstrates how to launch, and how to handle or send the required AppleEvents ('oapp' or 'odoc').

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Changing the 'SIZE' -1 resource multilaunch bit at run time

Date Written: 1/6/92

Last reviewed: 6/14/93

Can an application change its own 'SIZE' -1 resource to make it multilaunch, after the user personalizes it, so the application does a once-only write to itself? If we change the 'SIZE' -1 resource immediately after personalization and update the resource file, can other users on the network double-click the application before the very first user (who personalized it) quits?

You may certainly modify the 'SIZE' -1 resource in your application at run time. The only reason for not modifying the application file is that usually keeping a preferences file is much better for the user. Your situation leaves you no choice but to modify the app file itself. Unless you were to never store back into your app and create a preferences file for the initial configuration....

If you change your multilaunch bit, the application will need to quit before you can multilaunch it. When a single launch app is launched, it is opened with read/write exclusive privileges instead of multiuser privileges. So, no one else will be able to open the file to see that it is multilaunch until after you have quit. But, once you restart your application, it will be multilaunchable from then on.

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System 7 and MultiFinder's "puppet strings"

Date Written: 8/30/91

Last reviewed: 6/14/93

When my application is running, it relies on the MultiFinder's "puppet strings"(which choose Open from the application's File menu and suppress the SFGetFile dialog) to open a document that was double-clicked in the Finder. Why doesn't this work under System 7? The high-level event-aware bit in my 'SIZE' resource is clear.

System 7 will not pull puppet strings for an application that makes use of the System 7 Standard File routines, such as StandardGetFile and CustomGetFile, nor will it pull them if the application's high-level event-aware bit is set.

If you update an older application to take advantage of any System 7 features, be sure to also add support for the 'odoc' and other required Apple events.

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Background applications and alerts

Date Written: 5/4/90

Last reviewed: 6/14/93

My application, running in the background, detects an error condition and puts up an alert; but only part of the alert is visible (other windows cover most of it). When I switch back to my application, the full alert becomes visible but the "OK" is not highlighted and often the icon is not shown either. Is there something I can do to prevent this?

Applications running in the background should not be putting up alerts. In addition to the problems and complications you have already noted, under System 7.0 the user has the ability to hide a background application's window set and your alert would not be seen at the time you expect it to.

There is, however, a mechanism in place that your background application can and should use: the Notification Manager. Documented in Inside Macintosh Volume VI, this manager allows a background process to notify the user that there is an alert, message, or situation pending in the background that needs to be taken care of. The user can then bring your application forward and you can present your alert as the foreground application.

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Process Manager saves and restores the 68881/882 registers

Date Written: 5/3/89

Last reviewed: 6/14/93

Does the Process Manager save and restore the 68881/882 registers and state when it switches between applications?

Yes. As far as your application is concerned, it has the FPU to itself. The only time you need to worry about saving and restoring the FPU's state is when you are doing floating point operations at interrupt time, such as in a VBL or completion routine. Watch out for calls to the Sound Manager, since it will use floating-point operations internally.

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Acrobat version of this Note (33K).


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