Re: Extending protected types in 9X.

[eng.ufl.edu!usenet.ufl.edu!zeno.fit.edu!woodward@g.ms.uky.edu (Bill Wood]

In article <1993Aug17.072336.21830@sei.cmu.edu> wellerd@ajpo.sei.cmu.edu (David
 Weller) writes:
>As Tucker may vouch, this is my favorite subject.  Colin Atkinson
>and I have written a paper on this very subject.  It will be
>published in the proceedings of Tri-Ada '93 (look for it in your
>local bookstores soon!   NOT!).  
>
Any chance you could Email me a copy of your paper? I'm currently looking into
the improvements in Ada9X such as tagged types and protected types and I
would be interested in your views.

>The Reader's Digest version is:  No, protected types cannot be
>extended.  Nor can tagged types become "protected".  While it
>is true you may nest one kind of type within the record structure
>of the other, you fail to acquire the implicit benefits of that
>nested type.  If you spend a little time on it, you can see that
>extending protected types (or protecting tagged types) can turn into a
>small concurrency nightmare.  However, protected types were not
>really intended to be used in this manner (they were primarily
>intended for small, shared regions of memory that would be accessed
>by several tasks concurrently).  
>
But it would seem to be natural to extend some basic real time constructs
coded as protected types. Ex extend semaphores into counting semaphores
into mailboxes perhaps.


Bill Woodward				Florida Institute of Technology
woodward@se.fit.edu			Melbourne, FLORIDA

Plan:
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                        Projects, Tests, Thesis : OUT Requirements) is ......