Re: Tasks in Gnat3.05 for Dos?

[John Harbaugh <johnh@bunsen.ds.boeing.com>]

Spasmo wrote:
> 
> Robert Dewar (dewar@cs.nyu.edu) wrote:
> : "Yep found that out (how I missed it I'll never know).  Now it
> : compiles and runs, but the tasks don't run concurrently :("
> 
> : Of course they don't run concurrently, you are on a single processor
> : machine. Furthermore, in accordance with the required semantics of
> : the real time annex, the scheduling is run-till-blocked. If you
> : are thinking that I/O should be overlapped -- you won't get this
> : in DOS, DOS does not take kindly to multi-threading.
> 
> : What exactly are you expecting that you do not see?
> 
> Timeslicing.  IN any case that's not to be as many folks have told
> me, and now that I've started working on some tasking code, I find
> that it's actually a good thing since it's better that I implement
> my own atomic slicing based on units of work via different entries.
> 
> --
> Spasmo
> "Here's a present just for you
> When you open it, you'll be through"
>         "Letter Bomb" by the Circle Jerks

In their excellent book "Concurrency In Ada" Burns and Welling make a useful 
distinction between parallelism and concurrency:

"Two processes are said to be executing in parallel if at any instant they 
are both executing...  By comparison, two processes are said to be concurrent 
if they have the potential for executing in parallel."

The important principal is concurrancy.  A concurrent program will run 
correctly on one or many processors, or even a distributed heterogeneous 
network.  Performance depends on the actual hardware, of course.  Timeslicing 
is really just a way of simulating multiple processors.  A correct concurrent 
program will make no assumptions about the number of processors available.

	- John Harbaugh
	The Boeing Company
"Message disclaimers are not legally binding"