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Re: ObjC configured --with-objc-gc needs external Boehm gc
- To: Matthias Klose <doko at cs dot tu-berlin dot de>
- Subject: Re: ObjC configured --with-objc-gc needs external Boehm gc
- From: Helge Hess <helge dot hess at skyrix dot com>
- Date: Wed, 17 Jan 2001 12:12:38 +0100
- Cc: "Boehm, Hans" <hans_boehm at hp dot com>, gcc at gcc dot gnu dot org,java-discuss at sources dot redhat dot com, ovidiu at cup dot hp dot com
- Organization: http://www.skyrix.com
- References: <140D21516EC2D3119EE700902787664401E3A83E@hplex1.hpl.hp.com> <email@example.com.HOWL>
Matthias Klose wrote:
> Boehm, Hans writes:
> > The question is really whether the last pointer to an object can point to
> > the inside of the object. If you can get and save a pointer to a field in
> > object A, save it inside object B, and then drop the pointer to A, you need
> > ALL_INTERIOR_POINTERS. Thus C/C++ more or less need it, while Java doesn't.
> > If you can embed C structs inside Objective C objects, I suspect Objective C
> > also needs it?
> Then ObjC needs it as well.
I do not agree. It is theoretically possible, but irrelevant in practice
(it plays in the same league like ORing a ptr).
It doesn't make sense to hold *only* a ptr into the inside, since if you
don't have the ptr to the block-start, you can't reach 'isa' and
therefore this object isn't an ObjC object anymore.
Not storing a block-ptr is actually also problematic with
retain-counting as used in gstep-base or libFoundation as well.
An object is kept alive by it's handle and can only be messaged by a