220 35745 article Path: news.gmane.org!.POSTED!not-for-mail From: inkwizytoryankes@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Rotational shift operator Date: Mon, 4 Dec 2017 14:31:53 -0800 (PST) Lines: 109 Approved: news@gmane.org Message-ID: References: <69593098-e2cc-487e-bd14-9001b27aa7c1@isocpp.org> <3505307f-e3e8-47d2-bdae-8a45443057f8@isocpp.org> <2566183.A8JWrtnDUm@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_10113_368072834.1512426713302" X-Trace: blaine.gmane.org 1512426717 14627 195.159.176.226 (4 Dec 2017 22:31:57 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 4 Dec 2017 22:31:57 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDDLTAGNTIBBBWUZS7IQKGQEXK6BZTI@isocpp.org Mon Dec 04 23:31:52 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f70.google.com ([209.85.213.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eLzHA-0003Nk-Hu for gclcip-std-proposals@m.gmane.org; Mon, 04 Dec 2017 23:31:48 +0100 Original-Received: by mail-vk0-f70.google.com with SMTP id p143sf8226115vkf.1 for ; Mon, 04 Dec 2017 14:31:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=jVBcuAp9dkb2eBPdpvgKc9Jr74t24w/3JPXJeYWk4vU=; b=T9egvDGoVYfTkZ/aBvd5KEcMrgWVzU545BVQYXA7Rg+L04LHQoI0PHTVoyrDxub/Fm wKAbPdhS8O0i1x1LPgzpF1tNCJn8c8WhUKGUlvjcUgYpU2EOabIh9XLpX8sp0n83RRVr 0D67vCVgb+BuwuEBXweq8Tc7XutSKLaHh2cW7aLMHF6gurqCDtwEIDBA5VrEgGxW+xJb r6srjgbQLWB/W4MZcUuNwC03+w5QKN+y8heEZwdYNq1fMWd76knsOLn37/ZhppAV1p8a i27RjslYgnykkcR9zWKAgaSIVCinPL06e6Z7dLHlTDEQPoZYgrFKmlZEFmxcap+8//Bs 1qzg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=jVBcuAp9dkb2eBPdpvgKc9Jr74t24w/3JPXJeYWk4vU=; b=qn/5x3h62N2MjDEqR0ODP/km4Nz6e0fXczG3Fx2lL6UsCp5i9ZCOqNie6yOL6fIwB1 d8NEfR3yBChfJQLT0XLfHIaTA7qClpfelD5tE6KytcfTENKCpE1kvwUItKM/aGcHNNGW MVrZyZ8VKi9jo8OzsZLAktekVsOgQ2EGy0A29lQljbm3sDb7S/oaHk6X3HdI+65NzAoI j/9AiPityuygqAieq3f1YNhPRJQEbhyN71Ft84mqcjAFd/acsCrNc/pgew6k/Jo6+4Hs SfI9Dkp71uqDrCN2LOJarQt0Rnyx75R6L6/aw22mnB/j2P0dfr50b/0At9sx0JPpFBOp khaQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:x-original-sender:reply-to:precedence :mailing-list:list-id:x-spam-checked-in-group:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=jVBcuAp9dkb2eBPdpvgKc9Jr74t24w/3JPXJeYWk4vU=; b=YoXUojj9rJOCTIfsPdOyDQxPpn2rINlBlD+EUv0JQkExsWPvYVa0GXp+MhsfjfiAVQ 02Z9ZgrseMwcJKbSK+2lYW0RhYPledRu2/opS6G75mwOu4i0LtP7D9rFgEAAOHA1Cat0 IZY4osx+6yKhOo6e8kBi37ZLZyREt7RdtLI6u6ZUiea57UeZvNg4CuxfbamoDNShT0Ai bRZO5Dq0dzkQozsvoGzWHwtWlOnXvPBRMvaX3Klmgag+rzBJ5oM8rKK14a6p3FDG4lUW lqOFuGjcVlIB0LGXStECeXYIk5nE6Wg54Q7zrgYQnB9Gu55fMblXYGPB29ZpvuoSIi8f boyw== X-Gm-Message-State: AKGB3mLjq2vPPLa9l58Wn3JMsMS8ACQUOlsvoSX9MmLdH/GFzDGmf9sE z/8dqHAowBhK6UjusPHSLJK+iA== X-Google-Smtp-Source: AGs4zMYYZ69bjbAz6A9+HsGiTT6NHDItqTKRx5sB1EMWeb/G0M0EJq030wdwxjASATfF/fntRuJ28g== X-Received: by 10.159.54.115 with SMTP id s48mr334240uad.31.1512426715543; Mon, 04 Dec 2017 14:31:55 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.31.87.70 with SMTP id l67ls2536000vkb.6.gmail; Mon, 04 Dec 2017 14:31:54 -0800 (PST) X-Received: by 10.31.153.216 with SMTP id b207mr42444vke.8.1512426713922; Mon, 04 Dec 2017 14:31:53 -0800 (PST) In-Reply-To: <2566183.A8JWrtnDUm@tjmaciei-mobl1> X-Original-Sender: inkwizytoryankes@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:35745 Archived-At: ------=_Part_10113_368072834.1512426713302 Content-Type: multipart/alternative; boundary="----=_Part_10114_486970672.1512426713303" ------=_Part_10114_486970672.1512426713303 Content-Type: text/plain; charset="UTF-8" On Monday, December 4, 2017 at 11:10:02 PM UTC+1, Thiago Macieira wrote: > > On Monday, 4 December 2017 13:46:49 PST inkwizyt...@gmail.com > wrote: > > What is hard to understand in that? You allocate 100 objects then > releases > > some objects from that group. One page in the middle of this range have > > only deleted objects and no live one. > > Then allocator can detect this and inform OS that it can temporary grab > > this page because it contains only garbage. This will reduce total > memory > > usage without need to move any objects around. > > After that we create your special string that fall on boundary of this > > semi-released page. Until this page is not write then your last byte is > in > > garbage. When some other object is created in that page it switch it > status > > and if OS do not use it to other things it return it without change with > > old data. > > Actually, it's not garbage. If you give the page back to the OS but later > use > it, it will either give you exactly what you had before or it will give > you a > blank (zero-filled) page. So the value of that last byte is well known. > > Its garbage from perspective of allocator, same "garbage" like that left after you call destruction on some object. Usually C++ do not access data like this (but can if it backed by byte array and object was placement new constructed). -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/c98ed43e-4fbe-43ff-8e28-374184b565f3%40isocpp.org. ------=_Part_10114_486970672.1512426713303 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Monday, December 4, 2017 at 11:10:02 PM UTC+1, = Thiago Macieira wrote:
On Monda= y, 4 December 2017 13:46:49 PST inkwizyt...@gmail.com wrote:
> What is hard to understand in that? You allocate 100 objects then = releases
> some objects from that group. One page in the middle of this range= have
> only deleted objects and no live one.
> Then allocator can detect this and inform OS that it can temporary= grab
> this page because it contains only garbage. This will reduce total= memory
> usage without need to move any objects around.
> After that we create your special string that fall on boundary of = this
> semi-released page. Until this page is not write then your last by= te is in
> garbage. When some other object is created in that page it switch = it status
> and if OS do not use it to other things it return it without chang= e with
> old data.

Actually, it's not garbage. If you give the page back to the OS but= later use=20
it, it will either give you exactly what you had before or it will give= you a=20
blank (zero-filled) page. So the value of that last byte is well known.

Its garbage from perspective of allocator, same "= ;garbage" like that left after you call destruction on some object.
Usually C++ do not access data like this (but can if it backed by b= yte array and object was placement new constructed).

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+unsubscribe@isocpp.org.
To post to this group, send email to std-proposals@isocpp.org.
To view this discussion on the web visit https://groups.google.= com/a/isocpp.org/d/msgid/std-proposals/c98ed43e-4fbe-43ff-8e28-374184b565f3= %40isocpp.org.
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