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 18:00:42 +0200 Message-ID: <87h6nmdwph.fsf@dataswamp.org> References: <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> <83sf7acp86.fsf@gnu.org> <87led2x8ao.fsf@dataswamp.org> <83r0mtaupr.fsf@gnu.org> <87pm2ae19p.fsf@dataswamp.org> <83lecy5hps.fsf@gnu.org> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="6501"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) To: emacs-devel@gnu.org Cancel-Lock: sha1:vQe2CowW+EGkrRF1DtoOqLql7NQ= Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Fri Sep 22 20:06:00 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 1qjkXQ-0001Sb-Eq for ged-emacs-devel@m.gmane-mx.org; Fri, 22 Sep 2023 20:06:00 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qjkWk-0004F9-Q8; Fri, 22 Sep 2023 14:05:19 -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 1qjieY-0007Yb-N4 for emacs-devel@gnu.org; Fri, 22 Sep 2023 12:05:21 -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 1qjieQ-0007aJ-8z for emacs-devel@gnu.org; Fri, 22 Sep 2023 12:05:08 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1qjieL-0003FD-P3 for emacs-devel@gnu.org; Fri, 22 Sep 2023 18:05:01 +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 14:05:17 -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:310983 Archived-At: Eli Zaretskii wrote: >> There is no way around it, in order to prevent a race >> condition any global variable must be locked before it's >> value can be altered. >> >> So `setq', `setf' and any other setter of global variables >> must first be refered to the locking mechanism where they >> either acquire the lock, perform the write, and release the >> lock; or, if the variable is already locked by some other >> thread wanting to do the same thing, they must be queued so >> they will get it in due time. > > So one thread uses setq, releases the lock, then another > thread comes, takes the lock and changes the value of that > variable, and when the first thread uses the variable after > that, it will have a value different from the one the thread > used in its setq? How can one write a program under these > conditions and know what it will do? By relying not on global variables but on local variables. -- underground experts united https://dataswamp.org/~incal