Re: renames and access

[Stephen Leake <stephen_leake@acm.org>]

"Francesco Bochicchio" <bockman@virgilio.it> writes:

> Hi all,
> 
> I have a piece of code that does something like this:
> 
> type REC_T is record
> 	A : Integer;
> 	B : String(4)
> end record;
> 
> type REC_PTR_T is access REC_T;
> REC_PTR : REC_PTR_T := new REC_T;
> 
> A renames REC_PTR.A;
> B renames REC_PTR.B;
> 
> At this point, I can use A and B as if they where simple 
> variables. BUT, when I later reallocate the memory like this:
> 
> function REALLOCATE_MEMORY return REC_PTR_T;
> REC_PTR := REALLOCATE_MEMORY(); -- Actually, the ability to reallocate is
>                                 -- the reason for all this  fuss.
> 				--
> 
> then A and B still points to the old memory, not at the one currently
> pointed by REC_PTR.
> 
> Is this normal ??

Yes. The result of the rename statements is cached.

> Is there any way
> to have the renames to automatically points to the new memory? 

You have to evaluate them again after you change Rec_Ptr:

loop
  rec_ptr := Reallocate_Memory;
  declare
     a : Integer renames REc_ptr.a;
     b : string (4) renames REc_Ptr.b;
  begin
     ...
  end;
end loop

> If this turns impossible, what would be an equivalent solution? 

I need to see more context to suggest other ways of proceeding. Do you
have a loop like I wrote above?

> BACKGROUND : the reason for all this is that we are trying to add a
> failover capability to a very old application of many thousand lines 
> of code. Therefore, the 'critical variables' (one hundred or more) shall
> be allocated in a special area of memory which is mirrored between the
> primary machine and its backup, where  a copy of the application
> runs in hot standby. The trick with the renames should have spared us from
> changing every line of code referring to one of these variables.

Change the variables into equivalently named functions, whose bodies
reference the pointer. 

-- 
-- Stephe