Re: [Pyobjc-dev] Reference Counting

[Ronald O. <ous...@ci...>]

On 8-apr-04, at 17:54, Michael Tsai wrote:

> Hi,
>
> I've been happily using PyObjC to write little scripts for testing
> and automation. Now I'd like to use it to write some apps, and so I
> want to make sure that I don't leak memory and also have a
> reasonable memory high-water mark. The documentation says:
>
>     The `Cocoa libraries`_, and most (if not all) other class
>     libraries for Objective-C use explicit reference counting to
>     manage memory. The methods ``retain``, ``release`` and
>     ``autorelease`` are used to manage these reference counts. You
>     won't have to manage reference counts in Python, the bridge does
>     all that work for you.
>
> Wow, that's nice. However, I'm always a bit skeptical of unexplained
> magic, and indeed it doesn't appear to be *quite* that simple (even
> ignoring weakrefs). The code:
>
>     while 1:
>         NSArray.alloc().init()
>
> does indeed run with a constant amount of memory. However:
>
>     while 1:
>         NSArray.array()
> will use memory without bound unless I put in an autorelease pool:

That's correct, the bridge does not (and can not) hide the fact that an 
autorelease pool exists. This is not a problem in the normal use-case 
for PyObjC: writing GUI programs where you wouldn't use such a pool in 
Cocoa either.

[... some interesting examples where PyObjC seems to be leaking memory 
snipped ... ]

That's very interesting. I'm going to look into this, it's definitely 
my intention to make sure that the bridge won't leak memory.

BTW. What version of PyObjC are you using?

> One more question. It seems that PyObjC uses naming conventions to
> determine whether a selector transfers ownership. Does this mean
> that bad things will happen if I have an Objective-C class with an
> accessor method called -initialValue? That is, will PyObjC fail to
> retain the returned value because it thinks this is an -init method?

The method that tranfers ownership is named 'alloc', or 'copy'. The 
initializer doesn't come into play. Your example is a method name that 
is incorrectly recognized as an initializer, which does have a minor 
influence on the behaviour of the bridge, although not one that you 
should normally run into (the bridge knows that +alloc returns 
uninitialized objects and won't -release such objects unless an 
initializer method has been called).

Ronald
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