[haiku-appserver] Re: Shared Memory Allocation
- From: "Axel Dörfler" <axeld@xxxxxxxxxxxxxxxx>
- To: haiku-appserver@xxxxxxxxxxxxx
- Date: Sun, 05 Sep 2004 18:11:56 +0200 CEST
Adi Oanca <adi-oanca@xxxxxxxxxxxxx> wrote:
> > While shrinking an area is no problem, growing it usually is
> > (using
> > resize_area()).
> > There is no guaranty that the address space after that area is
> > still
> > available in which case the function will fail.
> I don't understand what you're saying here...
> Why resize_area() is not reliable? and why do you say the address
> space
> might be unavailable - because resize_area() might fail? If that's
> the
> case, we still can protect ourselfs.
The address space usage of an application is not predictable. In a
dynamic environment (such as an image processing app that may indeed a
large BShape/whatever object) it's very likely that resize_area() will
fail because the address range the growing area would need was already
given away for other purposes.
I.e. an area spanning from 0x40000-0x50000 cannot grow to 0x60000 if
this space is already occupied by another area - resize_area() will
fail in that case.
Therefore, an algorithm that's based on resize_area() to behave
properly (even with a code path in case resize_area() fails such as
recreating another big area and copying the old one) is a suboptimal
algorithm that shouldn't be used if speed is a concern.
Bye,
Axel.
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