Re: Tasks in ADA

[news.u.washington.edu!milton.u.washington.edu!mfeldman@beaver.cs.washingt on.edu (Michael Feldman)]

In article <463@rhlab.UUCP> bkuhn@rhlab.UUCP (bmk Bradley Kuhn) writes:
>
>   Is there a way to find out how a particular implimentation of ADA deals
>w/ tasks (i.e. time slicing or genuine multi-tasking).  I have read in ada
>manuals that in fact most ADA impimentations do time slicing, but I would 
>like to know for certian how our implimentation does it.  We are running
>ADA under VAX/VMS.  If anyone has any information I would greatly
>appreciate it.  (I would RTFM on VAX/VMS's manual for ADA, but at
>Loyola College in MD, the computer manuals are mostly not readily available
>to students).  Thanks.
>
Another writer may answer you for the specific case of VAX/VMS, but in the
general case, RTFM is really the only way to go. There's no requirement to
report this in a standardized fashion. Sufficient pressure on the lab
manager at Loyola should produce the manual. Get your prof behind you.

Time-slicing is not required, but preemption is required for tasks of
differing priority. That is to say that e.g. if a high-priority task goes
to sleep on a delay statement, giving the CPU to a lower-priority one,
the higher-priority task _must_ preempt the lower one upon expiration
of its delay. This requirement has always existed in theory, but it was
not graven in stone until an official interpretation promulgated in 1986,
and was not enforced by the validation suite until the current version,
1.11, which did not go into effect until 12/1/89.

Janus-Ada's tasking system is conforming by default, as they do not
support priorities. They say they'll do it "right" Real Soon Now.

Mike Feldman

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Michael B. Feldman                       co-chair, SIGAda Education Committee

Visiting Professor 1991-92               Professor
Dept. of Comp. Sci. and Engrg.           Dept. of Elect. Engrg. and Comp. Sci.
University of Washington FR-35           The George Washington University
Seattle, WA 98105                        Washington, DC 20052

mfeldman@cs.washington.edu               mfeldman@seas.gwu.edu
(206) 632-3794 (voice)                   (202) 994-5253 (voice)
(206) 543-2969 (fax)                     (202) 994-5296 (fax)
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