Re: trying to debug problems with NSAutoreleasepool

[Richard Frith-Macdonald]

On 2007-11-27 16:40:36 +0000 "Sebastian Reitenbach" 
<sebastia@l00-bugdead-prods.de> wrote:

> > Perhaps you have objects in the poolthat are crashing when they are 
> > released?
> I think, that seems to be the case. but how do I find out what kind 
> of 
> objects that are? The webui segfaults with the backtrace above, when 
> I think 
> it is emptying the last object from the pool, not sure about that. I 
> do not 
> fully understand what is going on there.

Understandable ... the autorelease mechanism is pretty performance 
critical, so it works hard to be fast and sacrifices some readability 
for speed.  While emptying a pool, the code caches method 
implementations to avoid having to do multiple method lookups for 
objects which are all of the same class.  It caches the 
implementations in a tiny hash table based on the address of the class 
(shifted right a few bits to allow for the fact that classes tend to 
be aligned on 4 or 8 byte boundaries, so the low few bits are useless 
as a hash).

> At least at ten places in opengroupware I commented out a [pool 
> release]; or 
> equivalent, to prevent these crashers.
>
> As I doubt, that commenting out these lines, is the right solution,
Almost certainly not ... that probably introduces a big memory leak.

Most likely you have a problem with objects being released more times 
than they are retained.

You can call [NSObject enableDoubleReleaseCheck: YES]; to turn on some 
checking for this ... but it will slow down your code quite a bit.

You can set the environment variable NSZombieEnabled to YES ... which 
will give you diagnostics about any attempt to use a deallocated 
object, but will use lots of memory.
You can also set NSDeallocateZombies to YES to avoid leaking memory as 
zombie objects, but this will give you less informative and less 
reliable (the memory from a deallocated object could have been re-used 
as another object) logging.