Date: Tue, 07 Dec 1999 20:40:27 +1100 (EST) From: Andrew Reilly <A.Reilly@lake.com.au> To: Wes Peters <wes@softweyr.com> Cc: freebsd-hackers@FreeBSD.ORG, Matthew Dillon <dillon@apollo.backplane.com> Subject: Bugs and their ubiquity (was an extended rant about PCI DMA) Message-ID: <XFMail.991207204027.A.Reilly@lake.com.au> In-Reply-To: <384CBED6.FECBC219@softweyr.com>
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Hi Wes, On 07-Dec-99 Wes Peters wrote: > Andrew Reilly wrote: >> >> On Sun, Dec 05, 1999 at 07:42:21PM -0700, Wes Peters wrote: >> > Software >> > is created by humans, and humans are fallible, therefore the >> > software is also fallible. >> >> No, that doesn't logically follow. Just because it's possible >> for humans to make mistakes doesn't mean that it's impossible to >> do or make something (eventually) without mistakes. > With the exception of TeX, *no* software is bug-free. In my > extensive experience, no software with the exception of TeX is free > of serious bugs. That's a little strong, don't you think? I can't remember encountering any bugs, serious or not, in any of the consumer electronics devices I use on a day-to-day basis. I've written a number of embedded signal processing applications myself that do exactly what they're supposed to, and don't ever break. I suspect that it's probably easier to be confident about code that does the same thing hundreds or thousands of times a second than code that will (with good luck and good management) never be run in anger, though. Using the example of TeX, what do you consider is special about it? A happy accident? Isn't it more likely that careful coding to a good design, with well defined inputs and outputs, and subsequent exposure to a great deal of peer review and testing has a little to do with it? How are those conditions different from those faced by any of the subsystems of FreeBSD, except perhaps by degree? > Your belief or lack thereof doesn't change the existence of > the bugs, it just leads YOU to be surprised when they crop up in the > oddest ways, while I am not. My beliefs haven't got much to do with it. Most of my interaction with my own software involves the belief that the subtle bugs are being masked by the obvious bugs. But I use the bugs that I find to teach me about my code and the states that it can find itself in. I leave assertions and invariant checks behind to make sure that the eroneous conditions don't re-occur, or re-design to accommodate them if they represent legal states. In my experience this beats any amount of interactive debugger single-stepping or crash-dump analysis. Remember: in the message that you quoted, I mentioned that the desirable state was one where we were "surprised at a crash of any sort", rather than "convinced by analytic proof that crashes were impossible". Sure, the difference between "surprised by crashes" and "surprised by lack of crashes" is one of degree, but it's a pretty important degree. My personal perception is that FreeBSD is currently much closer to the former state than the latter. Andrew To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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