Re: Ada Protected Object Tutorial #1

[Richard D Riehle <laoXhai@ix.netcom.com>]

In article <846rk7$gba$1@nnrp1.deja.com>,
	Robert Dewar <robert_dewar@my-deja.com> wrote:

>Really the point is that protected objects are best thought of
>as a framework for constructing very simple synchronization
>primitives with a minimum of active code. As soon as a protected
>object acquires complex internal logic, it is better represented
>by a separate Ada task.

Thanks for this clarification of your view.  The originaly phrasing
was something of a shock.  The real issue is that, when designing
for concurrency, one must select the mechanism best suited to the
problem to be solved.  Protected objects represent a significant
improvement over semaphores for mutual exclusion but need to be
used sparingly in a multi-tasking design.  As your note implies,
a protected object is not a substitute for a task.  Then again,
a task is not a substitute for a subprogram.  The difficulty of
designing with tasks is non-trivial, even when a rich set of
mechanisms is available, as in Ada.   

Richard Riehle