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 autolearn=unavailable autolearn_force=no version=3.4.4 Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!feeder.eternal-september.org!news.swapon.de!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: Niklas Holsti Newsgroups: comp.lang.ada Subject: Re: How to get Ada to ?cross the chasm?? Date: Wed, 9 May 2018 23:03:15 +0300 Organization: Tidorum Ltd Message-ID: References: <1c73f159-eae4-4ae7-a348-03964b007197@googlegroups.com> <87efiuope8.fsf@nightsong.com> <87lgd1heva.fsf@nightsong.com> <87zi1gz3kl.fsf@nightsong.com> <878t8x7k1j.fsf@nightsong.com> <87k1sg2qux.fsf@nightsong.com> <87h8njmk4r.fsf@nightsong.com> <87po27fbv9.fsf@nightsong.com> <87in7x62vw.fsf@nightsong.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Trace: individual.net X0IXSVXsygpC3cUqeAtZMAIqo2I1wgmDctlsSLe0s3eBLXn+9a Cancel-Lock: sha1:+DUi40dp4Qt88pinlopOD93wwDo= User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 In-Reply-To: <87in7x62vw.fsf@nightsong.com> Xref: reader02.eternal-september.org comp.lang.ada:52167 Date: 2018-05-09T23:03:15+03:00 List-Id: On 18-05-09 04:20 , Paul Rubin wrote: > Niklas Holsti writes: >> Some kind of WCET analysis is very often needed in real-time systems >> whatever kind of memory management is used. > > I'd say this is a niche area It is one of the core areas for the Ada language, and constrains the evolution of the language. > for which I'm surprised the methods we're > discussing are ever viable. Which methods are these? I'm perhaps lost. Reference counts are certainly viable for real-time systems, provided that long/deep chains of references are avoided (or handled by the "garbage list" method) which is often possible. Applicative data structures could be viable, if worst-case time and space bounds can be found -- even if they are less than tight. It seems that Dmitry uses such data structures, although he may not call them by this name. There has been a lot of work on and promotion of GC for real-time systems, but most practitioners are still not convinced. The real-time Javas tried to separate GC memory from non-GC memory, but it's been a while since I've seen any mention of real-time Java. > Remember that even traditional imperative > data structures like hash tables have terrible enough WCET that they > can't be used in realtime systems. So these systems have to be > programmed in special ways that are not very relevant to what's best for > the mainstream. There are alternatives (balanced trees, for example) which allow useful WCETs. There is also an area called "probabilistic WCET/timing analysis" in which WCETs are not single-valued, but distributions; if one can pick a "WCET" from the distribution such that the risk of the actual execution time exceeding this "WCET" is smaller than the risk of the HW failing, this "WCET" can be considered a realistic WCET. That could be a useful approach to the WCET of hash tables. (I'm emotionally repulsed by the probabilistic approach, but I have to admit it seems the only practical path for WCET analysis of current high-end processors. With the possible of exception of the Mill processor, under development.) >> Real-time systems with reference counting often use special "heaps" or > > I'd still like to know if there is careful analysis about max structure > depth and WCET, particularly formal analysis. Sorry, I don't understand what you want to know. Clarify, please. -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ .