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!news.eternal-september.org!mx02.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: Ada package registry? Date: Thu, 11 Feb 2016 09:25:57 +0100 Organization: Aioe.org NNTP Server Message-ID: References: <02241ec4-0f95-4f63-9abc-092f167eb59e@googlegroups.com> <56af17b7$0$301$14726298@news.sunsite.dk> <56b06eb8$0$301$14726298@news.sunsite.dk> <1454483747.2785.135.camel@obry.net> NNTP-Posting-Host: bqgfK7NL3xTHnr0WRaLl4g.user.gioia.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Complaints-To: abuse@aioe.org User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 X-Notice: Filtered by postfilter v. 0.8.2 Xref: news.eternal-september.org comp.lang.ada:29492 Date: 2016-02-11T09:25:57+01:00 List-Id: On 11/02/2016 02:37, Randy Brukardt wrote: > "Dmitry A. Kazakov" wrote in message > news:n9c9a8$mt9$1@gioia.aioe.org... >> On 09/02/2016 00:02, Randy Brukardt wrote: >>> "Dmitry A. Kazakov" wrote in message >>> news:n94cbv$19ed$1@gioia.aioe.org... >> >>>> For persistence layer you need dereference primitive operations. One for >>>> read access in order to cache data and one write access to mark the >>>> cache >>>> dirty. >>> >>> The first is the function call (to Reference, if you're looking at the >>> Ada >>> containers), and the second is the Finalize call that happens when the >>> object returned from Reference goes away. That was the whole point of the >>> design. (Of course, you could have written that in Ada 95, but without >>> the >>> syntactic sugar that makes it easier to read and write.) >> >> It is not same. A reference points to a proxy object, a cached copy of the >> external object in the persistent storage. When the proxy object is >> updated via any reference, it must be marked dirty. So that when the >> object at some point gets finalized or the transaction is committed it >> would be written back to the storage. > > But actually they are the same, because the reference can only exist for a > very short time. (You can't assign a reference because the accessibility is > too shallow.) Thus, the proxy object can be marked dirty (if you created a > writable reference, which is only created when you actually use the > reference in a writable context) and written back to the persistent storage. Writing objects is very expensive. So objects must be reference counted anyway. I don't see how the schema can handle all this, as well as inducing the reference type (read-only vs. read-write) from the context. > You do have to make sure that only one task is potentially writing a proxy > object at a time, but that seems like a good thing. Not good. Object updating through a reference and handling reference counts must be atomic. References must act as read-write locks. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de