Re: Sensible way to extend base class?
Re: Sensible way to extend base class?
- Subject: Re: Sensible way to extend base class?
- From: Michael Ash <email@hidden>
- Date: Wed, 20 May 2009 19:37:49 -0400
On Wed, May 20, 2009 at 7:30 PM, Greg Parker <email@hidden> wrote:
> On May 20, 2009, at 4:11 PM, Michael Ash wrote:
>>
>> On Wed, May 20, 2009 at 4:35 PM, Greg Parker <email@hidden> wrote:
>>>
>>> It's also much harder under GC. The "obvious" solutions either leak
>>> (because the global table keeps stuff alive), or are thread-unsafe (because
>>> no amount of locks can save your dangling pointer if the collector decides
>>> to delete the object).
>>
>> Is there something wrong with using a [NSMapTable
>> mapTableWithWeakToStrongObjects] in that environment, with appropriate
>> synchronization, or do you just consider that to be non-obvious?
>
> It's much improved over the traditional "CFDictionary with non-retaining
> callbacks" scheme, but is still vulnerable to uncollectable cycles under GC,
> if I remember correctly. If a table-value can eventually point back to its
> table-key, then the objects will never be reclaimed because of the table's
> own strong reference to the table-value.
That would indeed cause trouble. I hadn't thought of that. That means
that it's fine if you're storing relatively simple auxiliary data but
it's not appropriate for arbitrary objects. Thanks for the info.
Mike
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