[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Priority revisited: a new primitive

Adrian, et al,

> Until Barry or someone can tell us how to specify and implement high
> level requirements on the correctness of deadline driven programs in the
> presence of limited resources, I do not know how you can have a correct
> program that does not depend on priority.

The thing we're trying to control is scheduling.

A look at Stallings' "Operating Systems" gives us methods such as:
   * fixed priority scheduling
   * earliest-deadline scheduling using completion deadlines
   * earliest-deadline scheduling using unforced idle times
   * first-come first-served
   * rate monotonic scheduling
and this is not a complete list by a long way.

Note that priority is just one of many ways to control scheduling (and in
Stallings' example it is one that FAILS to meet the requirements).
It appears that you can't have a correct program that DOES depend on

Sorry, I don't have the answer - just problems and doubts.

Keep the discussion going.

| Barry M Cook, BSc, PhD, CEng, MBCS                                         |
| Senior Lecturer,                           Department of Computer Science, |
| Chartered Information Systems Engineer.    Keele University,               |
|                                            Keele,                          |
| Phone: +44 1782 583411                     Staffordshire,                  |
| FAX:   +44 1782 713082                     ST5 5BG,                        |
| email: barry@xxxxxxxxxxxxxx                UK.                             |