Re: [boost] [GIL] Can image::recreate reuse the memory?

Subject: Re: [boost] [GIL] Can image::recreate reuse the memory?
From: TONGARI (tongari95_at_[hidden])
Date: 2013-04-30 11:26:42

2013/4/30 Christian Henning <chhenning_at_[hidden]>

> > I think the code may have align problem in 2 respects:
> >
> > 1) line 336: _memory is not the aligned address which is previously
> > returned by align-function.
> >
>
> The function create_view is only called when reusing the image's memory. I
> guess I don't understand what you mean.
>

For example, look line 313: the memory address 'tmp' is aligned which may
differ from '_memory'.

So you can't recreate the view with _memory, instead, you should use the
aligned address.

> > 2) In 'recreate': You have to update _align_in_bytes before calling
> > create_view
> >
>
> When the user recreates an image with a different _align_in_bytes we need
> to reallocate the memory. I added this condition to the code. If the
> alignment doesn't change then I don't need to update the member.
>

You don't have to test the equality of _align_in_bytes & _alloc...
Even if _align_in_bytes differs, you could still reuse the space.
As for _alloc, I'm not sure if you want to guarantee that even if no
reallocation is needed, as long as the user provide another allocator, the
whole memory should be allocate by it.

I'm not sure how a allocator would be implemented, but since it's a default
param currently, while the user might just want to use the original one
(not the implicitly newly constructed one which may != the orignal), it
might surprise the user if he does care about the allocator used, so my
suggestion here is to separate it to 2 versions with & without allocator,
at least, it won't break the API (I personally would like to drop the
Alloc param here...)

Last but not least, 'total_allocated_size_in_bytes' also depends on
'_align_in_bytes', so nevertheless, you have to update it first.

HTH