Ada Task priorities

[kmradke@inav.net (Kevin Radke)]

Hello,

Can one guarantee how tasks at different priority
levels will be executed with respect to eachother?
(Speaking in both ada83 and ada95 terms...)

I.E. the following scenario:

  task a at the highest priority level
  task b at a priority level between the highest and lowest levels
  task c at the lowest priority level

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.

The ada83 RM seems to be pretty explicit about requiring "The
highest priority eligible task must be executing at any given
time", but the ada95 RM seems less verbose about this.  Even
annex D doesn't seem to require this. (Unless I missed something
obvious, which I probably have...)

My personal opinion is that using assumptions about priorities like this
is just asking for trouble, but I thought I would get other people's opinions
on this...

Thanks!
Kevin

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