Re: Ada Task priorities

[eachus@spectre.mitre.org (Robert I. Eachus)]

In article <dewar.854313404@merv> dewar@merv.cs.nyu.edu (Robert Dewar) writes:

  >> Can one guarantee that if all 3 tasks are eligible for execution
  >> at the same time, that task a will finish it's work before
  >> task b begins to run, and task c will only run after both
  >> tasks a and b finish? (Assuming no tasks rendezvous with
  >> other tasks during this time?)
  >> I suppose even OS calls would make this highly platform dependent.

  >   Of course not, think multiprocessors for a moment!

  Quite correct. There is another case to keep in mind.  If task a and
b read from disk, it is perfectly legitimate (in Ada 83 or 95) for c
to run while waiting for the I/O to complete.  This is usually a
special case of multiprocessing, but one most people overlook in
desktop systems.  (In embedded systems, I/O latencies are carefully
calculated and there is unlikely to be any disk I/O of any kind. ;-)

  In Ada it is possible to cover all the bases and get predicable
tasking behavior, but in modern systems you really have to understand
the underlying hardware design.

--

					Robert I. Eachus

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