Re: sending notifications in -dealloc

[Richard Frith-Macdonald]

On Friday, May 31, 2002, at 02:37 PM, Helge Hess wrote:

> Hi,
>
> maybe someone has an obvious answer ... This code does work on MacOSX 
> and libFoundation, but not on gstep-base:
> ---snip---
> - (void)dealloc {
>   ..
>   nc = [NSNotificationCenter defaultCenter];
>   [nc postNotificationName:@"ContextWillDeallocate" object:self];
>   ..
>   [super dealloc];
> }
> ---snap---
>
> I do this for weak references where I want to notify other observers 
> that the context is deallocated (they will reset their non-retained 
> pointer) ...
>
> This doesn't work on gstep-base, because the NSNotification created 
> retains and afterwards releases the "object:self". This somehow results 
> in a duplicate call to -dealloc (because the RC apparently reaches "0" 
> twice).
>
> Is anyone aware of differences with regards to RC in -dealloc or has 
> any other ideas ?

Interesting ... GNUstep implements the documented behavior -
retain increments the retain count (by calling 
NSIncrementExtraReefCount(), release decrements it
(by calling NSDecrementExtraRefCountWasZero()), and when it reaches zero 
dealloc is called.

So a retain within the dealloc will increment the retain count to 1, the 
release will decrement it to
zero, and dealloc will get called again.

Presumably MacOS-X  actually differs slightly from the documented 
behavior and does something like ignoring
any retain/release when the retain count is zero?
We could change GNUstep to work the same way for compatibility - though 
I think it would be a little less
efficient when built to user a map table for the extra reference counts.