From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.devel Subject: Re: Emacs design and architecture. How about copy-on-write? Date: Fri, 22 Sep 2023 22:00:04 +0300 Message-ID: <83fs3658zv.fsf@gnu.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> <87h6nmdwph.fsf@dataswamp.org> Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="10025"; mail-complaints-to="usenet@ciao.gmane.io" Cc: emacs-devel@gnu.org To: Emanuel Berg Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Fri Sep 22 21:00:55 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 1qjlOY-0002Qc-Tr for ged-emacs-devel@m.gmane-mx.org; Fri, 22 Sep 2023 21:00:54 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qjlNc-0007LE-RE; Fri, 22 Sep 2023 14:59:56 -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 1qjlNb-0007Fm-Ax for emacs-devel@gnu.org; Fri, 22 Sep 2023 14:59:55 -0400 Original-Received: from fencepost.gnu.org ([2001:470:142:3::e]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qjlNa-00084E-8Q; Fri, 22 Sep 2023 14:59:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=gnu.org; s=fencepost-gnu-org; h=References:Subject:In-Reply-To:To:From:Date: mime-version; bh=bhKSoRjB9LUmIpu6DHpoPHV/PQyaDMS1g+sFOs4aEwc=; b=NlpNZ8d/IQSk 96I7Lj7yBdeSZuL6Ou8gcYyF1NX8AY38YqEO30PYHYBqzpEgBUbDwnY8moi9Kvm5AMcBNj3mvd/2O 7mG6bn1KfVIuhOgyFrZud/TbYgYx8mul8TrO0tc1LKUOTFnhLlRrjyAW3cYHgMktdRePKzTNwOHLa ngLU939FjU+TQZf7sBG06TaGGwUDo8kHwm+R9GTGDarAJUA7VLpQhZdAKD1+StwWi91OLCKMsi6/b /mkP26AVcUtz1y/Nkkq9ZFRACO+coCxLTHOw/Mp/IPuNXt9HE/Lk2kLkRt+WBizld3YKDW1sZJeow X1NMp1Gt1pf7v9IYHxxMMQ==; In-Reply-To: <87h6nmdwph.fsf@dataswamp.org> (message from Emanuel Berg on Fri, 22 Sep 2023 18:00:42 +0200) 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:310987 Archived-At: > From: Emanuel Berg > Date: Fri, 22 Sep 2023 18:00:42 +0200 > > 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. It is impossible in Emacs to write a useful Lisp program that doesn't rely on global variables and other parts of the global state. You can only write toy programs without that.