Re: Leopard and Tiger Notification Differences?

FROM : John Stiles
DATE : Fri Feb 08 23:24:21 2008

It could be that Tiger is using -release in some place where Leopard is
using -autorelease. Either way is legitimate, but it would lead to the
kinds of effects that you're seeing.

If you follow the Cocoa memory management guidelines, it shouldn't
matter either way…


John Nairn wrote:
> I have run into several crashes in Leopard that never happened in
> Tiger. In all cases, the problem has been a notification sent to a
> deallocated object. I have been able to fix them, but why do these
> bugs keep happening in Leopard. Either Tiger was smarter (i.e., not
> sending messages to deallocated objects) or Leopard is handling
> notifications differently. I can document a difference now and wonder
> how is one supposed to know what to expect?
>
> These two lines respond to a menu command to delete a record of data
> being displayed in the main window
>
>    [[self document] performSelector:@selector(deleteRecordHere:)
> withObject:theRecord afterDelay:0.0];
>    [self close];
>
> The first line schedules a call to the document to delete the record's
> data. The close line closes the window and its controller. In Tiger,
> this works fine, but in Leopard in crashes, and tasks in the two
> systems happen in a different order. In Tiger:
>
> 1. The close causes the window controller to dealloc
> 2. Along with the window controller, all the interface objects from
> the nib file get deallocated
> 3. Finally, the deleteRecordHere: is invoked to remove data from the
> document.
>
> The exact same code in Leopard happens in a different order
>
> 1. The close causes the window controller to dealloc, but not the
> interface objects
> 2. The deleteRecordHere: method is invoked
> 3. Finally, after a delay, the interface objects are released.
>
> Now many times this order may not be important, but my particular
> application sends notifications while deleting the record that may
> happen to go to interface objects and those objects use methods in the
> window controller that owns them. Because the window controller was
> released, these notifications cause a message to a deallocated object
> and a crash.
>
> I solved the Leopard crash by moving my [self close] to another
> notification that gets calls when the record deleting is done in the
> document, but why would leopard split up the deallocation of a window
> and its objects into two sections and intersperse other scheduled
> methods in the middle? Is there a better way to get a selector called
> at a more convenient time? I want my delete record selector called
> only after the window and its objects are deallocated.
>
> ---------------
> John Nairn (1-541-737-4265, FAX:1-541-737-3385)
> Professor and Richardson Chair
> Web Page: http://woodscience.oregonstate.edu/faculty/Nairn
> FEA/MPM Web Page: http://oregonstate.edu/~nairnj
>
>
>
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