From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-0.8 required=5.0 tests=BAYES_00,INVALID_DATE autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f569d,7d68662d79c59f1c X-Google-Attributes: gidf569d,public X-Google-Thread: 109fba,46882e3fad98420e X-Google-Attributes: gid109fba,public X-Google-Thread: 103376,7d68662d79c59f1c X-Google-Attributes: gid103376,public X-Google-Thread: 102b75,7d68662d79c59f1c X-Google-Attributes: gid102b75,public X-Google-Thread: 1108a1,9292211c2d4756a8 X-Google-Attributes: gid1108a1,public X-Google-ArrivalTime: 1995-01-02 09:19:51 PST Path: nntp.gmd.de!newsserver.jvnc.net!netnews.upenn.edu!news.amherst.edu!news.mtholyoke.edu!uhog.mit.edu!sgiblab!swrinde!pipex!uunet!dove.nist.gov!news-reader.nist.gov!przemek From: przemek@rrdjazz.nist.gov (Przemek Klosowski) Newsgroups: comp.lang.c++,comp.object,comp.arch,comp.multimedia,comp.lang.ada Subject: Re: What's Real-Time? (was Re: Widespread C++ Competency Gap?) Date: 02 Jan 1995 17:10:52 GMT Organization: U. of Maryland/NIST Message-ID: References: <787227087snz@wslint.demon.co.uk> <3e26mc$n9u@Starbase.NeoSoft.COM> <3e5t1e$2ad@oghma.synapse.net> NNTP-Posting-Host: rrdjazz.nist.gov In-reply-to: rjc@oghma.synapse.net's message of 1 Jan 1995 04:35:42 -0500 Xref: nntp.gmd.de comp.lang.c++:84809 comp.object:19102 comp.arch:27411 comp.multimedia:25755 comp.lang.ada:17730 Date: 1995-01-02T17:10:52+00:00 List-Id: In article <3e5t1e$2ad@oghma.synapse.net> rjc@oghma.synapse.net (Robert J Carter) writes: >large 'hard' systems in the traditional sense are simply too >wasteful. An example is the telephone system. It is not 'hard real >time': the cost would be just too big. Instead, they figured out how >to manage available resources to have acceptably low failure rates. That's fine as far as it goes, but having done some work myself with reactor systems (I saw your sig), what is an acceptably low failure rate for the emergency shutdown system of a reactor? Of course the only acceptable failure rate for reactor emergency shutdown is zero. I was talking of failure in the sense of some tasks not meeting their deadline: e.g. if we have time, we shut down the pumps gradually, but if we are behind deadlines, we just scram them. The traditional ('bigoted', as the Dr. Dobbs article had it) real time has a discontinuous 'utility' function: one if the task finishes before deadline, minus infinity otherwise. The article claims that a more realistic approximation is a function like: utility to the system ^ | ----------|1 |\ | \ ---------------|--\--------> tardiness ( = time of completion - deadline) 0| \ | | BTW, I have nothing to do with the reactor design and operation: I am a solid state physicist, doing neutron scattering. -- przemek klosowski (przemek@rrdstrad.nist.gov) Reactor Division (bldg. 235), E111 National Institute of Standards and Technology Gaithersburg, MD 20899, USA (301) 975 6249