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From: Reto Buerki <reet@codelabs.ch>
Newsgroups: comp.lang.ada
Subject: Re: Barrier re-evaluation issue with GNAT 4.3.2
Date: Wed, 30 Sep 2009 16:12:46 +0200
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Date: 2009-09-30T16:12:46+02:00
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John B. Matthews wrote:
> In article <h9sgj7$1qr$1@news.eternal-september.org>,
>  Reto Buerki <reet@codelabs.ch> wrote:
> 
>> Jeffrey R. Carter wrote:
>>> An entry call is always potentially blocking, regardless of its barrier;
>>> see ARM 9.5.1. Technically, this code contains a bounded error. Since
>>> the potentially blocking operation was detected, your program should
>>> raise Program_Error; GNAT pretends that it hasn't detected that the
>>> operation is potentially blocking and lets you get away with only a
>>> warning. Other compilers (and even other versions of GNAT) may actually
>>> raise Program_Error.
>> Thanks for the clarification and the pointer to the ARM. This basically
>> means that our workaround is not legal Ada code ...
> 
> Well, it's a bounded error. Using Pragma Detect_Blocking, as suggested 
> by Bob Duff, will tell you if the compiler's warning is actualized at 
> run-time. As this is a work-around and your original code seems correct, 
> you might arrange things so that the original can be restored easily 
> upon upgrade or port.

The code runs correctly even though Program_Error is raised when
compiled with the Detect_Blocking pragma.

I think it's good enough as a workaround, we will upgrade to GNAT 4.4.x
as soon as possible.

Thanks for all your help!