Re: Languages don't matter. A mathematical refutation

[Dennis Lee Bieber <wlfraed@ix.netcom.com>]

On Sat, 04 Apr 2015 12:20:39 -0700, Paul Rubin <no.email@nospam.invalid>
declaimed the following:

>Dennis Lee Bieber <wlfraed@ix.netcom.com> writes:
>>>How big and complicated do those programs tend to be, if you don't mind
>>>my asking?  Do they have a lot of complex decision paths?
>> 	It's not decision paths so much as deterministic timing... If there is
>> a possibility of an operation triggering an arbitrary garbage collection
>
>Yes, I can understand why a realtime system can't use gc.  Writing
>simple programs without gc isn't too difficult.  Writing complicated
>programs without gc often means spending a lot of effort on manual
>memory management and debugging memory errors.  So I'm wondering if the
>programs you wrote that way were complicated and if yes, how you dealt
>with this issue.
>
	At present, I'm only on the fringe of things -- my 30 years at Lockheed
were on non-realtime number crunchers that ran one or two days in advance
of operations, for purposes of scheduling resources. My 2 years at GE
Aviation has been more debug support -- though what I've encountered has
been mostly the executive/device-driver layers; the end application tends
to be provided by the client using the documented APIs of the executive.

>In this case you may also have to consider the non-deterministic effects
>of cache misses, if your cpu has cache memory; similarly for pipeline
>stalls, serial multipliers, etc.

	It likely gets verified as part of the flight certification process. I
do know that multicore processors aren't currently supported due to such
conflicts.
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/