NSWindow & NSGraphicsContext issue

[Fred Kiefer]

Last week I tried to resolve a circular refernce problem between 
NSWindow and NSGraphicsContext.

The source of the problem is that when an NSWindow gets displayed it 
generates an NSGraphicsContext (or rather a subclass) which will then 
manage all the actual drawing. The window retain the context and the 
context has an info dictionary which includes the window. That way we 
already start off with a circular reference. To break this I released 
the window once, to adjust the retain count. Now when the window gets 
deallocated I first do a retain on it and then release the graphics 
context which will in turn result in a release on the window. Or so I 
hoped. There were a few issues with my original code. The graphics 
context and the dictionary where autorelease objects, so I had to 
postpone the deallocation of the window by returning from dealloc and 
let it be called again. This also needed a bit of isa sizzling as 
subclasses will not be aware of that reference counting trick and wont 
be prepared to get dealloc called twice. (And the code in NSWindow 
dealloc needed to be reentrant as well)

With that all resolved I expected my code now to work correctly, but 
this still isn't the case. As it turns out, calling retain on an object 
that already was about to get released wont have the expected result. 
When a release is send to an object with a retain count of 1, that count 
wont be changed! Now this means that I have to differentiate between 
calls to _termianteWindow that come from dealloc, where I don't call the 
retain and calls for oneShot windows, where I need to increase the 
retain count before freeing the context.

All of this now looks like an even bigger mess then the one I started 
with and now any help on how to clearly solve this would be welcome.

Cheers,
Fred

PS: Some of the code I talk about above is still not committed.