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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Ada advocacy
Date: Thu, 29 Aug 2013 21:47:58 -0700
Organization: Netfront http://www.netfront.net/
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Xref: news.eternal-september.org comp.lang.ada:17042
Date: 2013-08-29T21:47:58-07:00
List-Id: <comp.lang.ada>

On 08/29/2013 08:46 AM, Robert A Duff wrote:
>
>      protected P is
>          entry E1(...);
>          entry E2(...);
>      private
>          State: Enum := This_State;
>      end P;
>
>      protected body P is
>          entry E1(...) when State = This_State do
>          ...
>          end E1;
>
>          entry E2(...) when State = That_State do
>          ...
>          end E2;
>      end P;
>
> In task T:
>
>      select
>          P.E1(...);
>      else
>          ... -- (***)
>      end select;
>
> P is always in one of two states: willing to do E1, and willing
> to do E2.  At (***), we know that at the moment P.E1 was called,
> P was not willing to do E1, and was therefore willing to do E2.
> It is impossible for P to be in a state where it is not willing
> to do either E1 or E2.  (A state visible to clients, I mean.)

That's not quite right. P can also be executing E1 or E2, in which case it is not "willing" to do either. T will end up 
at (***) in both of those cases as well.

-- 
Jeff Carter
"Now go away or I shall taunt you a second time."
Monty Python and the Holy Grail

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