Re: D.10

[Matthew Heaney <matthew_heaney@acm.org>]

"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.