Re: A coding pattern that does not work under Garbage Collection

FROM : Jim Correia
DATE : Fri Nov 09 17:57:13 2007

On Nov 9, 2007, at 11:47 AM, Rick Hoge wrote:

>>> You kept a (default, no strong or weak modifier) pointer to data 
>>> inside the object, but no one kept a pointer to the object, so it 
>>> was collected.

>
> So if I had added the __strong modifier to the pointer assignment, 
> the collector would know not that the memory was still in use?


(Not a GC expert...)

No, I think you're still screwed. Since you can't know how NSData 
manages its bucket of bytes, you need to make sure the NSData object 
stays around for as long as you want to work with the bytes.

The salient point was that no one kept a reference to the object 
which owned the bytes you were pointing at, and when the object got 
collected as a result, it's internal storage also went away.

Really not so different from the autorelease case, except there you 
were guaranteed the lifetime of the parent autorelease pool. In a GC 
world the collector will collect unreferenced objects when it gets 
around to it, so you better keep a strong reference to the object for 
as long as you need it.

Jim