Re: rendez-vous underlying mechanism

["Pat Rogers" <progers@classwide.com>]

"Kevin Cline" <kcline17@hotmail.com> wrote in message
news:ba162549.0204080905.24486c34@posting.google.com...
> Richard Riehle <richard@adaworks.com> wrote in message
news:<3CA2A827.11140295@adaworks.com>...
> > Kevin Cline wrote:
> >
> > > "Bozo" <gri_nob@yahoo.com> wrote in message
news:<a7pk89$kj4$1@bcarh8ab.ca.nortel.com>...
> > > > Hi all,
> > > >
> > > > I'm sorry I wasn't clear enough.
> > > > I don't use ADA at the moment but I was a brave ADA programmer once.
> > > > I use C at the moment and I have a case where synchronous rendez-vous
would
> > > > be better that traditional asynchrounous intertask communications.
> > > >
> > > > Does anyone have an idea how to implement that in C with semaphores for
> > > > example ?
> > >
> > > This depends on the underlying OS.  If you are using pthreads,
> > > then see the manual entry for pthread_cond_wait.
> >
> > This approach, of course, does not come close to the capabilities
> > already built-in to the Ada tasking model.    Ever heard of protected
> > types.
>
> I know that.  However, in a hosted environment, the imperfect
> mapping between the Ada tasking model and the underlying OS facilities
> can catch programmers by surprise.

When was this?  You say that as if it is the current norm -- and it certainly
was in the 1980's -- but surely not still.  The compilers I know about that
target Un*x or Linux map tasks directly to the underlying OS's threads, not
their processes.  The old Verdix compiler did that many years ago (i.e., mapped
tasks to sprocs).

> I was certainly surprised
> when I attempted to create a separate task for I/O but found that
> all tasks blocked anyway because they were mapped to a single Unix thread.
> On that implementation Ada multi-tasking was uselsss for solving
> problems routinely handled with Posix threads.

Agreed; an undesirable implementation if the option of mapping tasks to Pthreads
was not available, but that's my point -- that was a given implementation that I
don't believe is not the norm today.

---
Patrick Rogers                       Consulting and Training in:
http://www.classwide.com          Real-Time/OO Languages
progers@classwide.com               Hard Deadline Schedulability Analysis
(281)648-3165                                 Software Fault Tolerance