220 15352 article Path: news.gmane.org!not-for-mail From: Ramkumar Revanur Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: get count of std::weak_ptr objects tracking a shared resource Date: Sun, 28 Dec 2014 08:01:41 -0800 (PST) Lines: 131 Approved: news@gmane.org Message-ID: References: <4797942.dAdOve4yz0@tjmaciei-mobl4> <2024731.u6vkxqVIEh@tjmaciei-mobl4> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_48_2133082613.1419782501073" X-Trace: ger.gmane.org 1419782509 29785 80.91.229.3 (28 Dec 2014 16:01:49 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 28 Dec 2014 16:01:49 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCD4HFPP7UBRBZWSQCSQKGQEIORTBAQ@isocpp.org Sun Dec 28 17:01:45 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yk0-f197.google.com ([209.85.160.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Y5GHn-0003QA-MQ for gclcip-std-proposals@m.gmane.org; Sun, 28 Dec 2014 17:01:43 +0100 Original-Received: by mail-yk0-f197.google.com with SMTP id 142sf37849249ykq.8 for ; Sun, 28 Dec 2014 08:01:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :content-type:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=KA2uBDZMmnS+xB3MSj+Wfq/wmMIz9NTASQHcc+Rud44=; b=E+2q0f02PyoQQvTHmaLBeXEJmZOUnG/5jpNq3O6slPH5H3j4EgTqrSvkuStNeTgv1W b97M66T+i4aFapSL+vb5eWKeSjpwprvmVrTFuZ+Cx7ejTZow7dquIrRxLwPpK8hGBQP6 ZdVolZpm7OmBqfKgFwmPytOq3Bh/w6CpX7d/GmsinTx0v/oSDnNtejAgxMU0egeUH7h5 p2MvoIOghrV+MKUC9Tuir2bmqPBMiALS6TqKOzpRIq6zUSSWVkUz6R8yTD8/wB8co6oP nnRjZeky1hTvnD33nafqxIbWQcbAIH/O2gR9Skd4jelPKhJHAakF4Rtn/Qtq5pdzMOsr 52+A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:content-type:x-original-sender:reply-to :precedence:mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=KA2uBDZMmnS+xB3MSj+Wfq/wmMIz9NTASQHcc+Rud44=; b=DFV6eyx5h/yC9GQZETmljFtcmyU52zId75aun1UNLNGTq8tp/+ADnHtDaBCNO0rPt9 hrjZaVjg8nuuv6S2TkmukNzb2Ji905nJil4EBDMjc+TLwFmBfa2sM1E76v6r8wQCC2ST Te128fkp8GZsGZI0mIdLQBcbgIzSQYhe0Hyn8lRDD1CCfYTQQ2sABlW4COIIRHNkbt09 vVuFU+8x6KOJEEsK1IQ987ZpGs2FsTP7xPX6ZTDP5e0F9rdsPzycEiHA1+ef/PXTAs5B BKPWYK5qTEOVpxqVdp2921qOiCUuWeUSUutzsMQYOBvLQztm+SMwjMI0MwKUeml4rEC1 XQcQ== X-Gm-Message-State: ALoCoQlw5jcdKk43s5z9nvnUgIlAZLuL6GrAHlRxKvBdDCgrG8nXOHpVMg4R2jGhIvIOo3JGrNw5 X-Received: by 10.236.202.207 with SMTP id d55mr42780685yho.4.1419782502651; Sun, 28 Dec 2014 08:01:42 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.129.165 with SMTP id l37ls5241502ioi.100.gmail; Sun, 28 Dec 2014 08:01:41 -0800 (PST) X-Received: by 10.50.110.101 with SMTP id hz5mr624799igb.6.1419782501957; Sun, 28 Dec 2014 08:01:41 -0800 (PST) In-Reply-To: <2024731.u6vkxqVIEh@tjmaciei-mobl4> X-Original-Sender: write2ramkumar@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:15352 Archived-At: ------=_Part_48_2133082613.1419782501073 Content-Type: multipart/alternative; boundary="----=_Part_49_627473673.1419782501073" ------=_Part_49_627473673.1419782501073 Content-Type: text/plain; charset=UTF-8 Look at the implementation of boost. http://www.boost.org/doc/libs/1_57_0/boost/interprocess/smart_ptr/detail/shared_count.hpp Boost has an implementation for weak_count! template class weak_count { ... }; On Sunday, December 28, 2014 7:33:06 PM UTC+5:30, Thiago Macieira wrote: > > On Saturday 27 December 2014 20:46:29 Ramkumar Revanur wrote: > > > "Not to mention that any value you get is stale the > > > moment you got it, since weak_ptr is thread-safe and the atomic > counter > > > may > > > have changed values already." > > > > The use_count on a shared_ptr will be as stale as the "weak_count" if > that > > was available. Does not mean it is not useful! > > Please see my other email about this. > > This function is not only returning stale info, it may return *incorrect* > information. The only condition under which it would return correct info > is > when you already know the information that it would return (that this is > the > only reference). > > -- > Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org > Software Architect - Intel Open Source Technology Center > PGP/GPG: 0x6EF45358; fingerprint: > E067 918B B660 DBD1 105C 966C 33F5 F005 6EF4 5358 > > -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. ------=_Part_49_627473673.1419782501073 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Look at the implementation of boost.

ht= tp://www.boost.org/doc/libs/1_57_0/boost/interprocess/smart_ptr/detail/shar= ed_count.hpp

Boost has an implementation for weak_= count!

template<class T, class VoidAllocator, =
class Deleter>
class weak_count { ... };



On Sunday,= December 28, 2014 7:33:06 PM UTC+5:30, Thiago Macieira wrote:
On Saturday 27 December 2014 20:46:29 Ramku= mar Revanur wrote:
> > "Not to mention that any value you get is stale the
> > moment you got it, since weak_ptr is thread-safe and the atom= ic counter
> > may
> > have changed values already."
>=20
> The use_count on a shared_ptr will be as stale as the "weak_count"= if that
> was available. Does not mean it is not useful!

Please see my other email about this.

This function is not only returning stale info, it may return *incorrec= t*=20
information. The only condition under which it would return correct inf= o is=20
when you already know the information that it would return (that this i= s the=20
only reference).

--=20
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
   Software Architect - Intel Open Source Technology Center
      PGP/GPG: 0x6EF45358; fingerprint:
      E067 918B B660 DBD1 105C  966C 33F5 F005 6EF4= 5358

--

---
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To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+unsubscribe@isocpp.org.
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