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Team Ada: Ada Programming Language Advocacy


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Sender: "Team Ada: Ada Advocacy Issues (83 & 95)" <[log in to unmask]>
X-To: "Harbaugh, John S" <[log in to unmask]>
Date: Wed, 11 Aug 1999 13:02:44 -0500
Reply-To: Pat Rogers <[log in to unmask]>
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From: Pat Rogers <[log in to unmask]>
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> 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.