From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Emanuel Berg Newsgroups: gmane.emacs.devel Subject: Re: Emacs design and architecture. How about copy-on-write? Date: Fri, 22 Sep 2023 17:59:03 +0200 Message-ID: <87jzsidws8.fsf@dataswamp.org> References: <0518f65b-1dd1-6923-8497-da4d3aeac631@gutov.dev> <87sf7fc7kd.fsf@dataswamp.org> <834jjuk68t.fsf@gnu.org> <87cyyhc7uu.fsf@dataswamp.org> <83ttrsg9nx.fsf@gnu.org> <83h6nrg4eg.fsf@gnu.org> <83v8c7elan.fsf@gnu.org> <877conk5ny.fsf@localhost> <83ttrreeu0.fsf@gnu.org> <87bkdzeas1.fsf@localhost> <83cyyfe5l8.fsf@gnu.org> <8734zbyu6o.fsf@dataswamp.org> <835y46e8o9.fsf@gnu.org> <87zg1ixvnc.fsf@dataswamp.org> <87il86nxts.fsf@localhost> <87o7hyx8h2.fsf@dataswamp.org> <87o7hx88ry.fsf@localhost> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="22723"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) To: emacs-devel@gnu.org Cancel-Lock: sha1:eCWU1928u3wh8wYXZSH2EueR7SE= Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Fri Sep 22 18:06:27 2023 Return-path: Envelope-to: ged-emacs-devel@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1qjifi-0005fT-B8 for ged-emacs-devel@m.gmane-mx.org; Fri, 22 Sep 2023 18:06:26 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qjieR-0007Mr-3Z; Fri, 22 Sep 2023 12:05:07 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qjiYm-00014N-Ja for emacs-devel@gnu.org; Fri, 22 Sep 2023 11:59:16 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qjiYk-000612-Ff for emacs-devel@gnu.org; Fri, 22 Sep 2023 11:59:16 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1qjiYi-0005hH-Gj for emacs-devel@gnu.org; Fri, 22 Sep 2023 17:59:12 +0200 X-Injected-Via-Gmane: http://gmane.org/ Mail-Followup-To: emacs-devel@gnu.org Mail-Copies-To: never Received-SPF: pass client-ip=116.202.254.214; envelope-from=ged-emacs-devel@m.gmane-mx.org; helo=ciao.gmane.io X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-Mailman-Approved-At: Fri, 22 Sep 2023 12:04:47 -0400 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.devel:310976 Archived-At: Ihor Radchenko wrote: >>> Because implementation details are tricky - a lot of Elisp >>> internal machinery is relying upon modifying global symbol >>> objects [...] >> >> Yeah, but that should be fine, as long as they are locked >> and unlocked safely, right? > > No. > > If we have something like (let ((case-fold-search t)) ...), > we will lock `case-fold-search' symbol for the whole > duration of `let' call and block any other threads trying to > alter `case-fold-search' locally. Yes, but so be it if that's the best we can do with `let' and a multi-threaded, multi-core Emacs. But one can also think of other ways to do that, for example local copies for the duration of the form. Overall, we will have to have a general solution, then examine Lisp forms that do global variable setting on a form-by-form basis and decide how they will relate to the general solution in the best way possible, while still playing by its rules. >> But, if one aspire to reduce the number of global variables >> used, a great way of doing that is lexical `let'-closures, >> here is an example that allows for the same default value >> when the function is called from Lisp and when used as an >> interactive command, yet the data is only hardcoded once >> for each variable. > > Not every variable can be used within lexical scope. > In particular special variables (see 12.10.4 Using Lexical > Binding and `special-variable-p') are always treated outside > lexical binding. We are never gonna come up with a bottom-level solution that works optimally for everything. Global/dynamic/special variables are the exception and not the norm - yes, as we hear from the name "special" BTW :) - and yes, they will have to be locked one by one and for as long as it takes for the execution to proceed safely. -- underground experts united https://dataswamp.org/~incal