On Apr 4, 2:33 am, stefan-lu...@[EMAIL PROTECTED]
wrote:
> Hi,
>
> I have written a little program to demonstrate finalisation. The idea is
> to locally declare a singelton object of a class derived from
> Ada.Finalization.Limited_Controlled, and to override the Finalize
method.
> When the sigelton object leaves scope, Finalize than cleans up whatever
> needs to be cleaned up. At a first look this appeared to work nicely.
But
> when done in a recursive subprogram, Finalize rather unexpectedly seems
to
> always read the local parameters of the innermost scope.
>
> Here is a test case:
>
> ---begin fin_test_case.adb
>
> with Ada.Text_IO, Ada.Finalization;
>
> procedure Fin_Test_Case is
> type Fin is new Ada.Finalization.Limited_Controlled with null record;
>
> procedure Do_Something (I: Natural) is
>
> type My_Fin is new Fin with null record;
>
> overriding procedure Finalize(Self: in out My_Fin) is
> S: String := Natural'Image(I);
> begin
> Ada.Text_IO.Put_Line(" Do_Something Finalization " & S);
> end Finalize;
>
> Singleton: My_Fin;
>
> begin -- Do_Something
> Ada.Text_IO.Put_Line(" I = " & Natural'Image(I));
> if I>0 then
> Do_Something(I-1);
> Do_Something(I-1);
> end if;
> end Do_Something;
>
> begin
> Ada.Text_IO.Put_Line("Start Do_Something (2)");
> Do_Something(2);
> Ada.Text_IO.Put_Line("Stop Do_Something (2)");
> end Fin_Test_Case;
>
> ---end fin_test_case.adb
>
> This is what I got:
>
> ---begin output
>
> Start Do_Something (2)
> I = 2
> I = 1
> I = 0
> Do_Something Finalization 0
> I = 0
> Do_Something Finalization 0
> Do_Something Finalization 0
> I = 1
> I = 0
> Do_Something Finalization 0
> I = 0
> Do_Something Finalization 0
> Do_Something Finalization 0
> Do_Something Finalization 0
> Stop Do_Something (2)
>
> ---end output
>
> Somehow, the local parameter I is always 0 when finalize is called. What
I
> expected was the following:
>
> ---begin expected output
>
> Start Do_Something (2)
> I = 2
> I = 1
> I = 0
> Do_Something Finalization 0
> I = 0
> Do_Something Finalization 0
> Do_Something Finalization 1
> I = 1
> I = 0
> Do_Something Finalization 0
> I = 0
> Do_Something Finalization 0
> Do_Something Finalization 1
> Do_Something Finalization 2
> Stop Do_Something (2)
>
> ---end expected output
>
> Now, is my expectation wrong? Or is this a compiler bug? I am using
> GNAT GPL 2007 (20070405-41).
This looks like a pretty clear compiler bug, especially since by the
time Finalize is called by the outermost Do_Something, it's using, for
the value of I, the parameter from a Do_Something call that is no
longer active. It shouldn't be hard to modify this slightly, using
(say) a string or record as a parameter to Do_Something, to create a
test where utter garbage is displayed; then it would be clearer that
this is a compiler bug.
-- Adam
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