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To: python-list@python.org
From: Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject: Re: Future of Pypy?
Date: Fri, 27 Feb 2015 18:47:27 -0500
Organization: IISS Elusive Unicorn
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On Fri, 27 Feb 2015 13:40:15 -0800, Paul Rubin <no.email@nospam.invalid>
declaimed the following:

>Steven D'Aprano <steve+comp.lang.python@pearwood.info> writes:
>> An interesting point of view: threading is harmful because it removes 
>> determinism from your program.
>> http://radar.oreilly.com/2007/01/threads-considered-harmful.html
>
>Concurrent programs are inherently nondeterministic because they respond
>to i/o events that can happen in any order.  I looked at the paper cited

	And that aspect (nondeterministic) applies whether one is using threads
or processes to handle the I/O -- except, possibly, in the types of
architectures used for aircraft systems: fixed time slices for "partitions"
(which /may/ run threads internally on a partition OS, but the entire
partition gets scheduled as a chunk by an overarching OS); no dynamic
memory allocations (and no freeing either) once the system transitions from
"startup" to "running" (any message queues have all "entries" pre-allocated
in a list); dedicated message queues for data transfer between partitions
vs within a partition, etc. Oh, and some designs require a partition to
essentially complete all processing within some total period of CPU time
(say, three partition time slices) and then, in effect, start over from the
beginning.


>Hmm, I see there's a Wikipedia article "Kahn process networks" about PN
>networks as mentioned, so I guess I'll look at it.  I see it claims a
>KPN is deterministic on its inputs, while I think CSP's might not be.
>
	Oddly, KPN wouldn't fit the hard realtime of aircraft systems -- it
fails on the "unbounded FIFOs".

	Wikipedia gives "deterministic" as (paraphrased) same inputs give the
same outputs -- but does not take into account the timing of the system.

KPN> Hence, timing of the processes does not affect outputs of the system.

	Deterministic /timing/ is a factor in aircraft systems.
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/