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!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: How to get Ada to ?cross the chasm?? Date: Sun, 6 May 2018 19:40:15 +0200 Organization: Aioe.org NNTP Server Message-ID: References: <1c73f159-eae4-4ae7-a348-03964b007197@googlegroups.com> <87k1su7nag.fsf@nightsong.com> <87po2la2qt.fsf@nightsong.com> <87in8buttb.fsf@jacob-sparre.dk> <87wowqpowu.fsf@nightsong.com> <16406268-83df-4564-8855-9bd0fe9caac0@googlegroups.com> <87o9i2pkcr.fsf@nightsong.com> <87in88m43h.fsf@nightsong.com> <87efiuope8.fsf@nightsong.com> <87lgd1heva.fsf@nightsong.com> <87zi1gz3kl.fsf@nightsong.com> <878t8x7k1j.fsf@nightsong.com> NNTP-Posting-Host: kQkuQcRDy1QFvWpyB1foYw.user.gioia.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit X-Complaints-To: abuse@aioe.org User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 X-Notice: Filtered by postfilter v. 0.8.3 Content-Language: en-US Xref: reader02.eternal-september.org comp.lang.ada:52044 Date: 2018-05-06T19:40:15+02:00 List-Id: On 2018-05-06 17:32, Niklas Holsti wrote: > On 18-05-06 12:53 , Dmitry A. Kazakov wrote: >> On 2018-05-06 10:34, Niklas Holsti wrote: >   ... >>> Moving the focus back to Ada, efficient applicative data structures >>> are interesting for real-time systems because they could reduce >>> locking/blocking times: a "reader task" could quickly grab a (logical) >>> immutable copy of a large data structure and read the data at its own >>> speed, without interfering with "writer" tasks that transform their >>> own (logical) copies of the data structure. >> >> You need to merge incoherent copies at some point later. > > In my applications, that would not be a big problem. In many cases the > writers can be serialized, in other cases writers update separate parts > of the data structure and merging would be easy. Other applications > could have more problems, but applicative data structures do tend to > provide high-level, merge-like operations. Maybe it is not a structure, but a set of assorted buckets of data? Maybe a simple monitor task with a queue would do the job? Whatever it is under real-time constraint you need to have each update visible within some bounded time interval. >> I have an intuitive feeling that in general lock-free approach does >> not work at large scale and is effective only at the low level and >> tight times. > > If the data structure is applicative, it does not have to be lock-free. > The applicative property should make lock holding durations very short > because the structure looks immutable to pure readers. "Applicative" is not a substantial property that hints any concrete implementation of publisher/subscribers bound through the data structure. If Ada should do anything, then provide much better support for user ADTs than it has now. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de