Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site utcs.UUCP Path: utzoo!utcs!geoff From: geoff@utcs.UUCP (Geoff Collyer) Newsgroups: net.unix-wizards Subject: Re: Access to kmem - System namelist - 'ps' etc (software interrupts) Message-ID: <277@utcs.UUCP> Date: Thu, 13-Dec-84 00:09:13 EST Article-I.D.: utcs.277 Posted: Thu Dec 13 00:09:13 1984 Date-Received: Thu, 13-Dec-84 00:59:13 EST References: <93@redwood.UUCP> Organization: University of Toronto - General Purpose UNIX Lines: 28 I beg to differ, Rob. I used TOPS-10 heavily for five years while in high school and university. I think that UNIX does most things better than TOPS-10 and in particular I don't think software interrupts nor asynchronous I/O should be grafted onto UNIX. Berkeley has taken the approach of trying to turn signals into perfect software interrupts and in doing so has complicated UNIX programs that wish to use signals correctly. If you wish to continue is this vein, then TOPS-10-style software interrupts and asynchronous I/O make some sense, but please, spare us the control blocks in user address space. The problem with software interrupts (and thus signal catching) is that they introduce asynchrony into user processes. Since asynchrony is a cause of hard-to-find timing bugs and since it complicates code which exploits it, I would prefer it to be sublimated into activities synchronous with user processes. The Thoth operating system (and more recently Verex and the V system) provides no form of asynchrony within a process, but rather provides cheap processes, message-passing and process destruction. In principle, something happening asynchronously with a process kills the process, doesn't affect it or generates a message for it. These mechanisms have proven sufficient for the tasks undertaken on Thoth and seem sufficient in general to avoid software interrupts and their associated bugs. This is somewhat simplified, but I have yet to see a genuine need for software interrupts, given a Thoth-like environment. I would suggest the Thoth book to anyone who wants more details (I think the full title is Multi-process Structuring and Portability: the Thoth System by David Cheriton, ex of Waterloo, now at Stanford).