Re: [GDL2] NSAutoreleasePool/EOFault

[David Ayers]

Manuel Guesdon wrote:

> Another idea is to return NULL in (instance)methodForSelector: to tell the 
> caller should not use imp or cache the method.
> It should be clean and safe isn't it ?
> The drawback is that callers should verify returned IMP and handle the 
> case...

I'm not sure which is worse here.  I think most developers may check 
with respondsToSelector: before caching the IMP but I doubt that they 
would then again check (instance)methodForSelector:.  And even if they 
did and tested all this against non-faulted object, the object can be 
faulted again by virtue of some indirect invalidation notification. 
EO(Fault)s and implementation casting simply don't work well together.

I've been trying to find some time to think about this.  But I don't 
think we can automagically deal with both optimizations.  Both have 
their merit but the just don't work well together.  We need to support 
EOFaults by design in GDL2.  And we should take care that we design any 
IMP caching optimization as EOFault tolerant as we can.  But I don't 
think that we should skip optimizations if we can insure them to be safe.

In the case of the NSAutoreleasePool, I think we are clear as each 
object is tested via GSObjCClass before the release is sent.  The fault 
will be cleared as soon as it is dealloced.  This may trigger other 
faults to fire, but then GSObjCClass will return the real class if those 
faults also still happen to be in the autorelease pool.

I've only done some preliminary testing but it seems that EOF's EOFault 
does not implement the class method's and that sending 
methodForSelector: fires a fault.  So EOF will also break with this scheme.

I agree with Richard, that this is all a bit worry some.  But by design 
those two optimization simply don't work to well together.  I think we 
could implement the EOFault class method instanceMethodForSelector: to 
accommodate the NSAutoreleasePool optimization, at least temporarily to 
unbreak GDL2.  Maybe add an NSWarnLog saying. @"Returning an EOFault 
instance implementation pointer for selector:".

I'm still a bit unsure on how to deal with the methodForSelector: class 
method.  But that's just because it looks like the issue seems unsolvable.

Cheers,
David