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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: D.10
Date: 1999/04/13
Message-ID: <m3lnfxtan3.fsf@mheaney.ni.net>#1/1
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References: <m3ogkuuriu.fsf@mheaney.ni.net>
 <7eu6ud$8lc$1@bgtnsc03.worldnet.att.net>
NNTP-Posting-Date: Mon, 12 Apr 1999 21:15:22 PDT
Newsgroups: comp.lang.ada
Date: 1999-04-13T00:00:00+00:00
List-Id: <comp.lang.ada>

"James S. Rogers" <jimmaureenrogers@worldnet.att.net> writes:

> Matthew Heaney wrote in message ...
> >Paragraph D.10 (7) states that
> >
> >"The operations Set_True and Set_False are atomic with respect to each
> >other and with respect to Suspend_Until_True..."
> >
> >
> >Q: Is Suspend_Until_True atomic with respect to Suspend_Until_True?
> >
> >In 12.3.1 of Burns and Wellings, they state that a semaphore can be used
> >to program mutual exclusion between two tasks, like this:
> >
> 
> Why not implement this as a protected object instead of a task. Protected
> operations are guaranteed to be atomic.


I am exploring primitive (but potentially more efficient) ways to
synchronize tasks.

The RM is ambiguous.  It doesn't say specifically that the suspension
object can be shared this way (ie that Suspend_Until_True is atomic wrt
other calls to Suspend_Until_True), but it doesn't say it can't be.

I would like to know the specific intent of the language designers, and
whether or not the algorithm in B&W is in fact legal.