Re: Non-NSObject object and garbage collection
Re: Non-NSObject object and garbage collection
- Subject: Re: Non-NSObject object and garbage collection
- From: "Ken Ferry" <email@hidden>
- Date: Wed, 13 Aug 2008 01:38:34 -0700
On Tue, Aug 12, 2008 at 11:30 PM, Quincey Morris
<email@hidden> wrote:
> On Aug 12, 2008, at 22:52, Ken Ferry wrote:
>
>> In general, you don't need to CFRetain an object to keep it alive
>> while it's on the stack. The fact that it's on the stack is enough.
>> If this wasn't true, there'd be a race, since the collector might
>> destroy the object before you retained it.
>
> Unless I misunderstand your point, its being on the stack will only keep it
> alive if CFMakeCollectable has already been called on it. In a case where
> you're given a CF-type object that you don't own, I don't think you can
> assume that. If it has not been made collectable, it's being kept alive by a
> non-zero retain count, or by having being autoreleased, either of which will
> keep it alive long enough for you to retain it.
I think Malcolm prefers we point at the docs rather than try to
explain in our own words. :-)
http://developer.apple.com/documentation/Cocoa/Conceptual/GarbageCollection/Articles/gcCoreFoundation.html
"By default, all Core Foundation objects are allocated in the garbage
collection zone."
"The difference between the garbage-collected environment and managed
memory environment is in the timing of the object's deallocation. In a
managed memory environment, when the object's retain count drops to 0
it is deallocated immediately; in a garbage-collected environment,
what happens when a Core Foundation object's retain count transitions
from 1 to 0 depends on where it resides in memory:
If the object is in the malloc zone, it is deallocated immediately.
If the object is in the garbage collected zone, the last CFRelease()
does not immediately free the object, it simply makes it eligible to
be reclaimed by the collector when it is discovered to be
unreachable—that is, once all strong references to it are gone. Thus
as long as the object is still referenced from an object-type instance
variable (that hasn't been marked as__weak), a register, the stack, or
a global variable, it will not be collected."
"CFMakeCollectable calls CFRelease, but has two supplementary
features: first, it ensures that the object was allocated in the
scanned zone; second, it's a no-op if you use managed memory. (In
addition, it more clearly signals your intent.) "
-Ken
Cocoa Frameworks
_______________________________________________
Cocoa-dev mailing list (email@hidden)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden