Re: Multitasking theory question

["AG" <ang@xtra.co.nz>]

"Darren New" <dnew@san.rr.com> wrote in message
news:3D173788.8758A005@san.rr.com...
> AG wrote:

> > Sure, it
> > may take ages for anything to happen if the computer is sufficiently
> > slow but you still can implement whatever scheduling you like.
>
> Uh, no. If you have a 3rd party device driver that blocks, then you can't
do
> non-blocking I/O to that device, regardless of what cleverness you set up
in
> your part of the program.

Well, let's take a step back and regard it as a theoretical question:
If you use something like "inc ax" - how do you know if it's blocking
or not? And how does it matter? Assuming the operation completes
*at all*, I still can write whatever scheduling I like and it will work
(albeit slowly). Basically, if you would allow some minimum set of
properties (like "inc ax" terminating in a finite time) then OS has
nothing to do with it. [Again, I agree that it may and, probably, would
be impracticable, but that doesn't mean it's impossible]

On the other hand, if you mean that scheduling can't be trusted because
of external mechanical faults which are non-deterministic - well, yes true.
You can also pull the cord from the plug and see what happens.

[Guess I'd better not cross-post *THAT* comment to VMS group:) ]