Re: INFO-ADA Digest V88 #47

[fortin@zap.UUCP (Denis Fortin)]

In article <8802202149.AA07429@ajpo.sei.cmu.edu> PETCHER%SVDSD@eg.ti.COM writes:
> Mike Linnig asks:
> > Is there a value to having multiple priorities even if we don't
> > have preemptive scheduling?
>
> My answer is an emphatic YES.  [...] in an embedded, real-time system
> tasks can be (and should be) designed to cooperate.  This means, among
> other things, a task should not execute indefinitely, and in fact should
> be designed to complete its intended function within a predictable
> period of time. 

Well, I agree that non-preemptive prioritized task scheduling makes
sense for some applications.  But in order for it to work, a task has to
be able to explicitly return the control to the "scheduler" when it has
expended its time slice. 

The only unobtrusive way I can see to force a rescheduling event to
occur in Ada is a "delay 0.0" statement.  Unfortunately, I'm told that
some compilers treat this as a no-op and simply ignore it.  Has anybody
encountered such a compiler? If so, is it legal? (section 9.6 of the LRM
does say about the delay statement: "The execution of a delay statement
evaluates the simple expression, and suspends further execution of the
task that executes the delay statement [...]")
-- 
Denis Fortin                            | fortin@zap.UUCP
CAE Electronics Ltd                     | philabs!micomvax!zap!fortin
The opinions expressed above are my own | fortin%zap.uucp@uunet.uu.net