> On a related note, I am curious as to how the Ada run-time system
implements dispatching.  Suppose task A is running at the highest
software priority and encounters a delay statement.  It then yields the
CPU to the next runable task of highest priority.  Okay so far, but what
happens when task A's delay expires?  How does the run-time system know
it should preempt the running task?  Do implementations rely on a timer
interrupt, or poll a list of delayed queues, or something else
altogether?  Perhaps one of the implementation folks would care to shed
a little light on a murky subject.

A timer interrupt is the way that is done -- the handler invokes the
dispatcher when necessary.