From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Marcin Borkowski Newsgroups: gmane.emacs.help Subject: Re: When are unused overlays garbage collected? Date: Wed, 26 May 2021 07:01:48 +0200 Message-ID: <874keqdr5v.fsf@mbork.pl> References: <87v978u3nd.fsf@mbork.pl> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="29901"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: mu4e 1.1.0; emacs 28.0.50 Cc: help-gnu-emacs@gnu.org To: Stefan Monnier Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Wed May 26 07:03:03 2021 Return-path: Envelope-to: geh-help-gnu-emacs@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 1lllh8-0007aJ-Pa for geh-help-gnu-emacs@m.gmane-mx.org; Wed, 26 May 2021 07:03:02 +0200 Original-Received: from localhost ([::1]:34456 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lllh7-0006Mz-TH for geh-help-gnu-emacs@m.gmane-mx.org; Wed, 26 May 2021 01:03:01 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:39300) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lllgN-0006Mo-Qs for help-gnu-emacs@gnu.org; Wed, 26 May 2021 01:02:15 -0400 Original-Received: from mail.mojserwer.eu ([195.110.48.8]:46552) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lllgI-0004Xd-5K for help-gnu-emacs@gnu.org; Wed, 26 May 2021 01:02:15 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by mail.mojserwer.eu (Postfix) with ESMTP id 5167AE6ACD; Wed, 26 May 2021 07:02:05 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at mail.mojserwer.eu Original-Received: from mail.mojserwer.eu ([127.0.0.1]) by localhost (mail.mojserwer.eu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id WZ3yu7sod066; Wed, 26 May 2021 07:01:51 +0200 (CEST) Original-Received: from localhost (178235147076.dynamic-3-poz-k-0-1-0.vectranet.pl [178.235.147.76]) by mail.mojserwer.eu (Postfix) with ESMTPSA id DCB5CE62EA; Wed, 26 May 2021 07:01:50 +0200 (CEST) In-reply-to: Received-SPF: pass client-ip=195.110.48.8; envelope-from=mbork@mbork.pl; helo=mail.mojserwer.eu X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.io gmane.emacs.help:130237 Archived-At: On 2021-05-24, at 19:07, Stefan Monnier via Users list for the GNU Emacs text editor wrote: >> My guess would be that if the overlay is "deleted" (so it is not >> attached to any buffer, either by means of `delete-overlay' or when its >> buffer is killed) /and/ it can't be referenced from Elisp (e.g., there >> is no variable bound to it). This would make sense, because even if >> there is no variable bound to an overlay which is not deleted, you can >> still get a reference to it using any of the overlay-finding functions >> (`overlays-at' or `overlays-in'). > > Sounds right, yes. `delete-overlay` just disconnects the overlay from > the buffer in which it was placed. As long as an overlay is placed in > a buffer, then it is still reachable (via internal variables inside the > buffer, and via `overlays-at' or `overlays-in') and it can have visible > effects on screen. Thanks! > Markers share some of their implementation with overlays, but because > markers do not affect the display and because there is nothing > corresponding to `overlays-at' or `overlays-in', Emacs goes through the > trouble of GC'ing those markers which are still reachable via the > buffer's internal variables (its list of markers) as long as they're not > reachable some other way, of course. Thanks, too, this is pretty interesting. I assume one possible reason for not having `markers-in' (analogous to `overlays-in') is that an overlay (even without any variable pointing to it, IOW, a "name" for it) has some "semantics" (properties), so it can be "guessed" what it is for; for markers, we would only know that "someone wanted to remember this position, but we have no idea why/what for", so why even bother keeping it? (Technically, there is also the insertion type, but that doesn't tell much, either.) > So it's OK to create markers are then forget about them, but it's not > OK to create overlays and then forget about them: you need to manually > `delete-overlay` when you're done with them otherwise they'll accumulate > in the buffer. And that is probably the most important takeaway here - but it raises another question. If I create an overlay in some buffer, keep no references to it, and then kill the buffer - is the overlay eligible for GC? (Again, I performed an experiment, and the results suggest that its state is similar to what happen after `delete-overlay', so I assume yes.) TIA, -- Marcin Borkowski http://mbork.pl