Re: ada paper critic

[Dmitry A.Kazakov <mailbox@dmitry-kazakov.de>]

Darren New wrote:

> "Dmitry A. Kazakov" wrote:
>> Actually I meant Ada's protected objects and not the visibility rules.
>> There is a great need to have protected objects extensible (tagged).
>> At the same time it is not very clear (at least to me), how to do it.
> 
> What's wrong with Java's approach to OO threading and protected objects?

I do not know Java good enough to judge. But the problems as I see them are 
mostly with MD and MI. Java has no MD. Ada has neigher. But if it had, how 
to call on an entry point that belongs to two protected objects, or else 
tasks? Consider imaginary:

task type A;
task type B;
entry Do_It (First : in out A; Second : in out B); -- Of both A and B

task type C is new A with ...;
entry Do_It (First : in out C; Second : in out B); -- Overrides in A

   X : A'Class := ...; Y : B'Class := ...;
begin
   select
      Do_It (X, Y); -- Dispatching entry call
   ...

What about freezing rules with MD? May I override barriers? How to override 
the body an entry point of a task? How to inherit an entry point? How to 
add a new entry point? From a caller view point, there is no difference 
between entry points of tasks and protected objects, should then exist a 
common parent type for them? Should caller know any difference between an 
entry point and a subroutine? Isn't that an implementation detail? If so, 
how to [efficiently] implement entry points with a return parameter? Or 
should we introduce generic formal entry points, protected type, task type 
parameters?

I suspect lots of pitfalls here. However, ask more knowledgeable people 
than me ...

-- 
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de