Re: Barrier re-evaluation issue with GNAT 4.3.2

["John B. Matthews" <nospam@nospam.invalid>]

In article <h9sgj7$1qr$1@news.eternal-september.org>,
 Reto Buerki <reet@codelabs.ch> wrote:

> Jeffrey R. Carter wrote:
> > Reto Buerki wrote:
> >>
> >> Update: we just noticed that the warning actually *does* show up but we
> >> missed it in the previous build.
> >>
> >> I also think the warning is irrelevant. It seems that the compiler is
> >> not smart enough to figure out that the Signal() entry is always open.
> > 
> > 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.

Because this can be a maintenance headache, you might also look through 
some other examples of Timing_Events with a view towards your intended 
usage:

<http://www.adaic.com/standards/05rat/html/Rat-1-3-4.html>
<http://www.adaic.com/standards/05rat/html/Rat-5-6.html>

-- 
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>