Re: memory management in Ada: tedious without GC?

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 19 Maj, 17:37, Matthew Heaney <mhea...@on2.com> wrote:

> > 1. No support for exception-safe assignment in Ada.
>
> It depends on how you define "exception-safe".

I meant strong safety (either all OK or nothing modified).

> Assignment in Ada
> makes only a "basic guarantee" wrt exception safety

Yes.

> (State is not preserved
> because finalization of the LHS happens before the assignment proper.)

Note also that it prevents some obvious optimizations like avoiding
memory allocator round-trip when for example short container is
assigned to a longer one, which already has enough place for RHS.

> > 2. Memory leak after exception is raised while initializing the
> > allocated object in Ada.
>
> If by "initializing" you mean invoking a controlled action

I meant initialization of components like here:

type T is record
   X : Integer := Initialize_Me;
end record;

It can be any exception other than Program_Error, including user-
defined one.

> I do forget the exact rules about memory reclaimation, though;
> if I do
> this:
>
> declare
>   P : T_Access := new T;
> begin
>
> and the initialization of the object designed by P fails (e.g. because
> controlled initialization fails, which raises Program_Error, or
> because component initialization fails, which raises
> Constraint_Error), then what does the language say about reclaiming
> the memory allocated for P.all?

The memory is lost.
OK, it is still managed by the relevant storage pool - but if the pool
itself is not dynamically scoped (or the scope is just too wide), then
it is effectively a leak.

--
Maciej Sobczak * www.msobczak.com * www.inspirel.com