Re: High-Integrity OO and controlled types

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

On Wed, 04 May 2011 16:46:21 +0200, Georg Bauhaus wrote:

> On 04.05.11 11:28, Dmitry A. Kazakov wrote:
> 
>> This does not read as a complete description. In what sense are the parts
>> of the array shared? If sharing means only independent use of the parts,
>> then what sense has the array as an object in this design? Independently
>> used parts must be local to their users. Now, if there is something else
>> behind this, i.e. that parts are sometimes used independently and sometimes
>> together, then too little is said about the mechanisms used for the latter,
>> and most intricate part of design.
>> 
>>> This sounds like one could design types that
>>> do(!) just this as part of their finalization.  But it does
>>> seem like an awful lot of overhead, and is essentially
>>> a type that is-a procedure.
>> 
>> You see that as an overhead only because the picture is incomplete. Once
>> you fill the gaps, you will see how "exit action" firs there. That would
>> definitely involve additional objects, e.g. controlled "handles" of which
>> finalization would deal with "exit" and other operations would serve
>> interlocking etc.
> 
> A simple example (full source linked, but may not be
> necessary); the intention is for it to be fairly low
> level data manipulation.  It is not nice, and could be
> generalized in several ways, I think.  If there is
> justification for doing so.
> 
> Array `Central` is manipulated by two tasks A and B.
> When these have finished filling `Central`, the env task
> computes the final result by counting certain values in `Central`.
> Communication uses simple variables and visibility.
> 
> The task B is sensitive to a special piece of input
> and will restart its work from the beginning when
> the input testing function raises Junk_Signal.

This looks like the "checkpoint synchronization problem".

   http://rosettacode.org/wiki/Checkpoint_synchronization

I would use a protected object to implement an array of events and
distributing jobs among the worker tasks when they join or leave. I would
likely place the array there. I would avoid polling.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de