Re: rendez-vous underlying mechanism

[Darren New <dnew@san.rr.com>]

Ole-Hjalmar Kristensen wrote:
> Agreed, but it would be reasonable to see a language standard specify
> that blocking a task would not block the entire program. It's a pity
> it's not covered in the Ada standard.

I think you'd get into all kinds of things about what "blocking a task"
means. For example, for a while I worked on one system where requesting
to allocate memory when there wasn't any swap space left got you swapped
out until some other program freed up memory. There's no way to not
block all the tasks if your process isn't in core. And it's just a
memory allocation doing this, not even any user-visible I/O.
 
If a task calls "suspend my processes until the operator mounts the
tape", it's hard to guess whether you want the other threads running or
not.

In UNIX-land it can be pretty easy to guess. Making such guesses
portable could be problematic. Providing a list of what OS calls will
block all threads is probably about as close as you can come, but that
wouldn't have solved the original problem, since the I/O that blocked
your code would have just been on that list.

-- 
Darren New 
San Diego, CA, USA (PST). Cryptokeys on demand.
      Remember, drive defensively if you drink.