Re: Presentations on-line - Ada&SPARK for Education&Research

[Peter Hermann <p@s.de>]

Georg Bauhaus <rm-host.bauhaus@maps.futureapps.de> wrote:
> I'm reading a few presentation pages that advertise  the strengths
> of Ada. One sheet compares monitor functionalities as present
> in Java and Ada.  Java needs much care not to break
> a monitor.  Ada is shown not to have this problem.
> 
> True?  With some effort, it seems possible to break an Ada
> monitor implemented as a protected object.
> 
> package Monitor is
> 
>     type SynchNode;
>     type Linkage is access all synchnode;
>     type data is access all integer;
> 
>     protected type synchnode is
>        procedure Link (x : Linkage);
>        procedure Expose (N : out Data);
>     private
>        Outgoing : aliased Integer := 0;
>     end SynchNode;
> 
> end Monitor;
> 
> package body monitor is
> 
>     protected body synchnode is
>        procedure link (X : Linkage) is
>           View : Data; -- X's data
>        begin
>           X.Expose(View);
>           View.all := View.all + 1;  -- <-- unprotected
>        end link;
> 
>        procedure Expose (N : out Data) is
>        begin
>           N := Outgoing'unchecked_access;

monitor.adb:69:24: warning: possible unprotected access to protected data

>        end expose;
>     end SynchNode;
> 
> end Monitor;