Re: rendez-vous underlying mechanism

[Ole-Hjalmar Kristensen <oleh@vlinux.voxelvision.no>]

kcline17@hotmail.com (Kevin Cline) writes:

> 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.  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.

Yes. The really bad thing about this is that your program will compile
and run, but not work as you had expected when you port it to a new
platform where Ada tasks has been impelented differently.