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=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM autolearn=ham autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,ce6f6f23c4e880ad X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2002-06-24 18:59:48 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!paloalto-snf1.gtei.net!news.gtei.net!enews.sgi.com!news.xtra.co.nz!53ab2750!not-for-mail From: "AG" Newsgroups: comp.lang.ada References: <3d123f34.0@news.unibw-muenchen.de> <3D128BA9.8090707@telepath.com> <3D16B14B.2A5D8261@attbi.com> <3D173788.8758A005@san.rr.com> Subject: Re: Multitasking theory question X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 5.50.4522.1200 X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4522.1200 Message-ID: Date: Tue, 25 Jun 2002 14:01:23 +1200 NNTP-Posting-Host: 210.54.67.222 X-Complaints-To: newsadmin@xtra.co.nz X-Trace: news.xtra.co.nz 1024970388 210.54.67.222 (Tue, 25 Jun 2002 13:59:48 NZST) NNTP-Posting-Date: Tue, 25 Jun 2002 13:59:48 NZST Organization: Xtra Xref: archiver1.google.com comp.lang.ada:26680 Date: 2002-06-25T14:01:23+12:00 List-Id: "Darren New" wrote in message news:3D173788.8758A005@san.rr.com... > AG wrote: > > Sure, it > > may take ages for anything to happen if the computer is sufficiently > > slow but you still can implement whatever scheduling you like. > > Uh, no. If you have a 3rd party device driver that blocks, then you can't do > non-blocking I/O to that device, regardless of what cleverness you set up in > your part of the program. Well, let's take a step back and regard it as a theoretical question: If you use something like "inc ax" - how do you know if it's blocking or not? And how does it matter? Assuming the operation completes *at all*, I still can write whatever scheduling I like and it will work (albeit slowly). Basically, if you would allow some minimum set of properties (like "inc ax" terminating in a finite time) then OS has nothing to do with it. [Again, I agree that it may and, probably, would be impracticable, but that doesn't mean it's impossible] On the other hand, if you mean that scheduling can't be trusted because of external mechanical faults which are non-deterministic - well, yes true. You can also pull the cord from the plug and see what happens. [Guess I'd better not cross-post *THAT* comment to VMS group:) ]