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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Allocation question
Date: Mon, 11 May 2009 05:18:59 -0700 (PDT)
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Date: 2009-05-11T05:18:59-07:00
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Olivier Scalbert wrote on comp.lang.ada:
> 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
> > =A0 =A0type Image_T (Width, Height : Natural :=3D 0) is private;
> > private
> > =A0 =A0type Data_T is array(Positive range <>, Positive range <>) of
> > Color_T;
> > =A0 =A0type Data_Access_T is access Data_T;
> > =A0 =A0type Image_T (Width, Height : Natural) is
> > =A0 =A0 =A0new Ada.Finalization.Controlled with record
> > =A0 =A0 =A0 Data : Data_Access_T;
> > =A0 =A0end record;
> > =A0 =A0overriding procedure Initialize (Object : in out Image_T); --
> > allocates
> > =A0 =A0overriding procedure Adjust(Object : in out Image_T); -- duplica=
tes
> > Data.all?
> > =A0 =A0overriding procedure Finalize(Object : in out Image_T); --
> > deallocates
> > end Image;
>
> > with Image;
> > declare
> > =A0 =A0Im1 : Image.Image_T (1 .. 1024, 1 .. 1024); -- calls Initialize
> > which allocates
> > =A0 =A0Im2 : Image.Image_T (0, 0); -- calls Initialize which does nothi=
ng
> > begin
> > =A0 =A0Im2 :=3D 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
> =A0 =A0 =A0Ada.Text_IO.Put("Initialize");
> =A0 =A0 =A0-- What shall I put here ?
> end Initialize;
>
> Olivier.

Read the Object's Width and Height (the discriminants can be read like
any other component). Allocate the Data_Array_T on the heap with the
corresponding size. Assign the result to Object.Data.

--
Ludovic Brenta.