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From: robert_dewar@my-dejanews.com
Subject: Re: tasking in Ada and Annex D question
Date: 1999/02/03
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References: <793jl9$hf@drn.newsguy.com> <796jj7$5s2$1@pegasus.csx.cam.ac.uk>
 <796v4e$16e$1@nnrp1.dejanews.com> <797m6h$73g$2@pegasus.csx.cam.ac.uk>
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Date: 1999-02-03T00:00:00+00:00
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In article <797m6h$73g$2@pegasus.csx.cam.ac.uk>,
  mgk25@cl.cam.ac.uk (Markus Kuhn) wrote:
> What I have a bit of a problem to understand is, for what
> else apart from preemptive scheduling, concurrency when
> system calls block, and utilization of multiprocessor
> systems do I need tasks for (i.e., all the things FSU
> doesn't do)?

My goodness! A surprising question. Multi-threading is
a very fundamental programming paradigm for all sorts of
situations. Endless examples are at hand, but here's just
one, a radar tracking program where each trace is a
separate task. Such applications may not even do any
system calls! There are lots of large scale applications
using Ada tasks which don't care two hoots about system
calls. Note as an example that many of the Ada 83 compilers
in which tasking was used heavily did their own scheduling
within a single process in Unix (or DOS!)

The mapping of tasks into OS threads is a relatively new
development. It is useful for certain kinds of system
programming, but there is a very high efficiency penalty
to be paid for this approach, a penalty which many (most?)
applications do not need to pay.

P.S. of course FSU threads provides preemptive scheduling,
this is required by the RM semantics!

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