Re: why use "task"?

[franke@minet.uni-jena.de (Frank Ecke)]

On Mon, 17 Aug 1998, Dr. Hubert B. Keller <keller@iai.fzk.de> wrote:

>Tasking is mostly to model concurrent behavior on a single processor
>machine.
>Please keep in mind, that parallel execution on a single processor is only
>a model that works
>not always in real.

IMHO, on the abstract level, one should not get bogged down by the actual
number of processors and, indeed, most concurrent programming languages (Ada
amongst them) consider it to be immaterial whether there is a single processor
or a multi-processor system.  Ada says:

``Concurrent task execution may be implemented on multicomputers,
multiprocessors, or with interleaved execution on a single physical processor.
On the other hand, whenever an implementation can determine that the required
semantic effects can be achieved when parts of the execution of a given task
are performed by different physical processors acting in parallel, it may
choose to perform them in this way.'' (Ada 95 Reference Manual, Section 9)


Note that this is a NOTE, i.e., it should not be the programmers concern how
the implementation actually works.  Of course, someone designing realtime
systems ought to pay attention to this subject. But for general application of
concurrency?


>Parallel execution is only done in real on a n processor for n tasks
>machine.

Well, the number of processors is fixed but the number of tasks can vary as
they can be created/destroyed at runtime.  Hence, we could---from the abstract
point of view---always restrict ourselves to a single processor.


Regards,

Frank