TECHNOTE 1095Object Support Library Version HistoryBy Andy BachorskiApple Developer Technical Support (DTS) devsupport@apple.com |
CONTENTSIn the Beginning of OSLThe World As We Know It Known Bugs in the OSL Download OSL 1.2 |
This Technote is an attempt to clarify
the version history of Apple's Object Support Library (OSL). This library
provides routines that applications can use to support the
Open Scripting Architecture (OSA) object model. OSL was originally released as a 68K static library. With the introduction of Power Macintosh systems, OSL was repackaged as a shared library. When the Code Fragment Manager 68K Runtime Enabler (CFM-68K) was released, it became a fat library containing both Power PC and CFM-68K versions of OSL. This Technote lists all versions of OSL that are currently available along with a brief history and description of each one, and recommendations as to which versions to use (and not use). If you develop Macintosh applications that provide OSA object model support, or need to use applications that do, you should read this Technote. |
In the Beginning of OSL
When the OSL was first released, it was a 68K static library
(
With the release of the Power Macintosh and the accompanying CFM shared library
application model, it was decide that a shared library version of the OSL
(
The OSL PowerPC shared library was released as version 1.0.2. It was
included with the first Power Macintosh system software (version 7.1.2) and the
AppleScript SDK version 1.1. It is currently still available on the Mac OS SDK CDs.
This version of the OSL has a number of known bugs in its handling of
This first shared library introduced the first OSL shared library problem. The OSL was written in Pascal, but there were no PowerPC Pascal compilers, so it contained a small PowerPC-native library that loaded a 68K code resource containing the OSL.
But this loading was not done properly; the After the introduction of the Power Macintosh, work began to convert the OSL source code from Pascal to C. This conversion was needed in order to provide a shared library containing both PowerPC and CFM-68K code. The converted fat OSL was released as version 1.0.4, which was included on the E.T.O. CD-ROM releases until recently. There were a number of problems, however, with this version of the OSL, the worst of which was that a Gestalt selector installed by version 1.0.2 was not being installed by version 1.0.4. This prevented applications that were testing for this Gestalt selector from detecting the presence of the OSL shared library.
Note: A Gestalt selector is not the best method for detecting
the presence of the OSL, but this decision was made early in the development of the code
fragment model and the liabilities of using Gestalt were not yet well
understood. The preferred method would have been to have developers compare a
symbol in the library to The other major problem with this version of the OSL was a number of bugs in the code that
handled |
No Code Changes, Just Version ChangesSomewhere between versions 1.0.2 and 1.0.4, a mistake was made in the build process for the AppleScript 1.1 SDK which led to version 1.0.2 of the OSL being released as version 1.1. There is no difference in the actual code, only a new version number. This meant we now had a 1.1 version which is really older than version 1.0.4. But installers complain when you try to install v1.0.4 over 1.1 because they think you are replacing a newer version with an older one. So when Apple shipped the Apple Telecom software version of OSL, 1.0.4 was changed to 1.1.1. This allowed the installer to replace the old version with the new. Again, no code changes, just a version change. (All the old problems, of course, were still there). This is the point where many people started having problems; we now had a situation where a (generally) well-behaved version 1.1 was being replaced with a broken version 1.1.1. |
A Valiant Attempt To Fix ThingsThe AppleScript team, at this point, decided that enough was enough -- it was time to move forward and fix things. They released a version that fixed the Gestalt selector problem and called it 1.1.1. But no one had told them about the Apple Telecom OSL version 1.1.1, so they changed the version to 1.1.2. But, again, someone else had already made a limited release of an OSL version 1.1.2.
This was unfortunate, but not a major problem -- they just incremented the version to 1.1.3.
This version, which contained the fixed Gestalt selector, got a limited developer
release. Great -- now the applications which couldn't load it before due to the
Gestalt selector bug could use the OSL. But when these applications loaded the OSL,
they revealed all sorts of interesting behaviors resulting from the OSL's
inability to resolve |
Back to the Drawing BoardThe AppleScript team started looking at the 1.0.4/1.1.1 code stream in more detail and, after considering what a fix might mean to the stability of existing applications, it was decided that the risk of further trouble was too great. The decision was made to return to the older 1.0.2/1.1 code stream for the next release of the OSL. As a result, the resource-loading source stream in version 1.0.2 was revised so it could be compiled as a native PowerPC and CFM-68K library. The resource-loading bug was also addressed. This revised library was tested, sent to a small group of developers for further testing, and then approved for final build as version 1.1.4. Along the way, though, there was a new wrinkle added to this story. In order to fit in with the Mac OS reference release strategy, the file's creator type got changed, along with with its version number, which changed to 1.1.6.
But we still have more to our story. It seems that the test suite used to validate the OSL tested for the presence of the Gestalt selector, but did not determine if it was properly installed. Basically, native OSL resource-loading code wasn't doing the right thing when it installed its Gestalt selector, which could lead to crashes in certain situations. In the meantime, Version 1.1.6 was included as part of the Harmony (Mac OS 7.6) f3 build that was seeded to developers. When this latest OSL problem was discovered, the decision was made to take the version 1.0.2 of OSL and reversion it (again) as version 1.1.8. This is the version of OSL that is included in the GM version of Mac OS 7.6. The biggest problem with this version is that it isn't fat, as it doesn't contains CFM-68K code (recall that 1.0.2 didn't, either). This wasn't an immediate problem, since Mac OS 7.6 shipped without support for CFM-68K. In fact, 7.6 explicitly checks for the presence of the current CFM-68K extension and disables it to prevent its loading with this version of the system. If you can't run CFM-68K, you don't need a fat OSL. A New HopeThanks to the efforts of a number of engineers, the OSL got a more thorough rewrite which fixed both the Gestalt selector and resource file bugs. The testing was completed and the problems were resolved. This time, the OSL was released as version 1.2, which now generally works as expected. It still contains the bugs related towhose clause resolution, but they are not fatal
and are easy for developers to work around (see
Known Bugs in the OSL).
|
Known Bugs in the OSLThere are still several known bugs in the OSL, but they all have workarounds. Unlocked Handles Passed To Compare Functions
You can install an object comparison function for use when resolving The problem here is that the memory blocks containing the descriptor records pointed to by the parameters are located in relocatable blocks that are not locked and may move after the compare function is called. The workaround for this problem is to copy the descriptor records pointed to by the parameters to a local variable as soon as you enter the object comparison routine.
There is a complication to this problem involving Classic 68K applications
and the segment loader. If the comparison function and the
The workaround for this problem is to make sure that the comparison function
and the |
Memory Leak in Object Comparison Callback Function During
|
Pascal versionfunction MyCompareObjects( comparisonOperator: DescType; (CONST) VAR theObject: AEDesc; (CONST) VAR objOrDescToCompare: AEDesc; VAR compareResult: boolean): OSErr; var theObjectCopy : AEDesc; objOrDescToCompareCopy : AEDesc; begin { First make copies of the descriptors because the OSL has them pointing into a relocatable block, which can be moved by the code below. } theObjectCopy := theObject; objOrDescToCompareCopy := objOrDescToCompare; { Now set the original desciptors to the null descriptor since we have to dispose of the objects below because of this OSL bug! } SetToNullDesc( theObject ); SetToNullDesc( objOrDescToCompare ); { Code to do the comparison goes here } MyCompareObjects := DoTheComparison( comparisonOperator, theObjectCopy, objOrDescToCompareCopy, compareResult ); { These descriptors are supposed to be const, but the OSL never calls our dispose token callback function, so we dispose of them here in case one of them is an application-defined token. } MyDisposeToken( theObjectCopy ); MyDisposeToken( objOrDescToCompareCopy ); end; |
C versionOSErr MyCompareObjects( DescType comparisonOperator, const AEDesc *theObject, const AEDesc *objOrDescToCompare, Boolean *compareResult ) { AEDesc theObjectCopy; AEDesc objOrDescToCompareCopy; OSErr anErr; theObjectCopy = theObject; objOrDescToCompareCopy = objOrDescToCompare; SetToNullDesc( theObject ); SetToNullDesc( objOrDescToCompare ); anErr = DoTheComparison( comparisonOperator, theObjectCopy, objOrDescToCompareCopy, compareResult ); MyDisposeToken( theObjectCopy ); MyDisposeToken( objOrDescToCompareCopy ); } |
Memory Leak in
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Function to set descriptor record to null descriptorvoid SetToNullDesc( AEDesc theObject ) { theObject.descriptorType = typeNull; theObject.dataHandle = nil; } |
Special thanks to Chris Espinosa, Roger Pantos, Bryn Oh, and Otto Schlosser.
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