From bill@amber.ssd.csd.harris.com Tue Aug 18 15:18:20 1992 Received: from travis.csd.harris.com by dkuug.dk via EUnet with SMTP (5.64+/8+bit/IDA-1.2.8) id AA29477; Tue, 18 Aug 92 15:18:20 +0200 Received: from amber.ssd.csd.harris.com by travis.csd.harris.com (5.61/harris-5.1) id AA05296; Tue, 18 Aug 92 09:18:22 -0400 Received: by amber.ssd.csd.harris.com (5.61/CX/UX-5.0) id AA08385; Tue, 18 Aug 92 09:18:12 -0400 Date: Tue, 18 Aug 92 09:18:12 -0400 From: bill@amber.ssd.csd.harris.com (Bill Leonard) Message-Id: <9208181318.AA08385@amber.ssd.csd.harris.com> To: JLS@liverpool.ac.uk Cc: SC22WG5@dkuug.dk In-Reply-To: Lawrie Schonfelder's message of Tue, 18 Aug 92 12:55:37 BST <9208181224.AA04572@travis.csd.harris.com> Subject: (SC22WG5.156) Defect Report X-Charset: ASCII X-Char-Esc: 29 > Date: Tue, 18 Aug 92 12:55:37 BST > From: Lawrie Schonfelder > If I know the pointer is there I can but If I dont because it is a component > of a type whose structure is PRIVATE I dont. If I understand you correctly, then, the problem is that Fortran 90 invented PRIVATE types but neglected to provide constructors and destructors so they could be properly initialized. Is that right? > The inefficiency of having to set disassociated each > pointer as it is created is spurious. In any system that does full garbage > collection, which any high quality implementation must do. It must distinguish > between not yet associated and genuinely dangling or it would be impossible > to produce safe garbage collection. First of all, this comment is not true. Most garbage collection systems for languages like C, Ada, Pascal, etc. do conservative garbage collection. That means that if a memory location contains something that looks like a pointer into the heap, then the pointed-to location is considered "used" and therefore not garbage to be collected. Second, it would be a colossal mistake to *mandate* garbage collection in all Fortran implementations. I'm not saying that garbage collection is universally bad -- it certainly has lots of useful applications. But it does have a couple of very bad characteristics. One of these is that the garbage collector tends to touch all of memory fairly often. That's very bad for virtual memory systems if the application gets very big. Second, garbage collection introduces extreme unpredictability in timing, which is anathema in the real-time industry. (How would you like your neighborhood chemical plant to explode because the monitoring system didn't respond to an alert in the proper amount of time?) > The cost of setting any not-yet-associated flag will be pretty much the > same as setting disassociated. If you dont like initially disassociated I > would settle for an additional status of not-yet-associated and some way > of detecting this fact in the Fortran program. But, as you just pointed out, the two are the same cost. Since I object to the first one on the basis of its cost, I'm unlikely to accept your alternative. Bill Leonard Harris Computer Systems Division 2101 W. Cypress Creek Road Fort Lauderdale, FL 33309 bill@ssd.csd.harris.com --------------------------------------------------------------------------- Q: How many lawyer jokes are there? A: Only three. The rest are true stories. ---------------------------------------------------------------------------