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Date: Mon, 11 May 2009 14:14:03 +0200
From: Olivier Scalbert <olivier.scalbert@algosyn.com>
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Subject: Re: Allocation question
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Date: 2009-05-11T14:14:03+02:00
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Ludovic Brenta wrote:

> Yes. Your image is on the stack. You can increase the size of the
> stack up to an operating-system-dependent maximum (see ulimit(1) on
> Unix-like systems) but there is always a limit. For potentially very
> large objects, I think the better approach is to allocate them on the
> heap. I would suggest you hide the allocation and deallocation inside
> a controlled object which you declare on the stack, e.g.
> 
> private with Ada.Finalization;
> package Image is
>    type Image_T (Width, Height : Natural := 0) is private;
> private
>    type Data_T is array(Positive range <>, Positive range <>) of
> Color_T;
>    type Data_Access_T is access Data_T;
>    type Image_T (Width, Height : Natural) is
>      new Ada.Finalization.Controlled with record
>       Data : Data_Access_T;
>    end record;
>    overriding procedure Initialize (Object : in out Image_T); --
> allocates
>    overriding procedure Adjust(Object : in out Image_T); -- duplicates
> Data.all?
>    overriding procedure Finalize(Object : in out Image_T); --
> deallocates
> end Image;
> 
> with Image;
> declare
>    Im1 : Image.Image_T (1 .. 1024, 1 .. 1024); -- calls Initialize
> which allocates
>    Im2 : Image.Image_T (0, 0); -- calls Initialize which does nothing
> begin
>    Im2 := Im1; -- calls Finalize (Im2) then Adjust (Im2)
> end; -- calls Finalize for both
> 
> You may also share image data between objects.
> 
> For even larger objects you can make Initialize, Adjust and Finalize
> much more sophisticated and store parts of the object on the heap and
> part on disk. You would do that only if you think you can beat the
> performance of your kernel's paging subsystem.
> 
> HTH
> 
> --
> Ludovic Brenta.

Thanks Ludovic.

procedure Initialize (Object : in out Image_T) is
begin
     Ada.Text_IO.Put("Initialize");
     -- What shall I put here ?
end Initialize;


Olivier.