220 13025 article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Compile-time static `std::integral_counter` Date: Sat, 20 Sep 2014 07:32:29 +0800 Lines: 103 Approved: news@gmane.org Message-ID: References: <9a0bde7b-2f0a-4a5b-92a4-88d5e8df7ea9@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_48C506D6-33DF-4AC5-9FC9-9883D2C39E0D" X-Trace: ger.gmane.org 1411169571 7089 80.91.229.3 (19 Sep 2014 23:32:51 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 19 Sep 2014 23:32:51 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBGX26KQAKGQECX4UCMA@isocpp.org Sat Sep 20 01:32:44 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ig0-f200.google.com ([209.85.213.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XV7fQ-00019r-3d for gclcip-std-proposals@m.gmane.org; Sat, 20 Sep 2014 01:32:44 +0200 Original-Received: by mail-ig0-f200.google.com with SMTP id hn15sf2314272igb.7 for ; Fri, 19 Sep 2014 16:32:43 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:message-id:mime-version:subject:date :references:to:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=x9uuzdtvQZUFT+5xf/XEhZr/JYwv5h58WFWbCr9KMu0=; b=VJdTSN/XPsIKjEyrR5PrXRERfSpNhNDxZBskKUcUMDrbU4T7J7uDHNUta+jwUaoJRE tsbPjJo9uZ5vOpTLoUcQKvRv1BQmGwLMvmsPVoBwTTG8u3/RCzoVyh7S3KhoHrCxKS24 +HlZX5YYG2vQu0+d+zVzAybQQjdZKz1x20WdJ9kLunWA34OnXEl7yLyg8YjHqhVIFhap E9+NGGezYa9SBWakQ45kCJ9MWSpqkrH2FIeUF/ktdsFfBsFD5TDy7O+mSzjdtCCqq3Le +A4Uc/qEtS7DL3sBNLoEZWYioLqWL7gmhZmQeUnfJbmdY8HG5FUEggrdI4en1no9xcRH r5nQ== X-Gm-Message-State: ALoCoQlHZQcfjLPWaSILarmaxMJNHfFO+e/dVaL51WUarZ3ycXnf+8GupwaSVUR2G9hRa5wAbR4k X-Received: by 10.43.71.81 with SMTP id yj17mr13554970icb.26.1411169563233; Fri, 19 Sep 2014 16:32:43 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.61.148 with SMTP id p20ls752144igr.38.canary; Fri, 19 Sep 2014 16:32:42 -0700 (PDT) X-Received: by 10.68.106.162 with SMTP id gv2mr4483651pbb.17.1411169562299; Fri, 19 Sep 2014 16:32:42 -0700 (PDT) Original-Received: from mail-pd0-x229.google.com (mail-pd0-x229.google.com [2607:f8b0:400e:c02::229]) by mx.google.com with ESMTPS id d8si5052786pat.120.2014.09.19.16.32.42 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 19 Sep 2014 16:32:42 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c02::229 as permitted sender) client-ip=2607:f8b0:400e:c02::229; Original-Received: by mail-pd0-f169.google.com with SMTP id w10so823447pde.0 for ; Fri, 19 Sep 2014 16:32:42 -0700 (PDT) X-Received: by 10.66.139.106 with SMTP id qx10mr5751253pab.126.1411169562163; Fri, 19 Sep 2014 16:32:42 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.54.151]) by mx.google.com with ESMTPSA id w11sm2811020pbt.84.2014.09.19.16.32.39 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 19 Sep 2014 16:32:41 -0700 (PDT) In-Reply-To: X-Mailer: Apple Mail (2.1878.6) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c02::229 as permitted sender) smtp.mail=potswa@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=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:13025 Archived-At: --Apple-Mail=_48C506D6-33DF-4AC5-9FC9-9883D2C39E0D Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=ISO-8859-1 On 2014-09-20, at 1:40 AM, Vittorio Romeo wr= ote: > On Friday, 19 September 2014 19:23:22 UTC+2, David Krauss wrote: > I see some discussion of the ODR in this thread. Any counter usage with l= inkage does need to be placed in the header file and repeated exactly the s= ame in each TU. Avoid sharing a counter between headers unless those header= s are all-or-nothing. >=20 > Can you elaborate more on this? What I am currently doing is putting the = workaround code in an header file (header-only library) and using inline in= every function. Is that not guaranteed to return expected values in differ= ent TUs? (values that never repeat, I mean) It's in reference to the StackOverflow answer. If the counter values are assigned at runtime, it's sufficient to have exte= rnal linkage (inline or not) on some object or function which does the coun= ting. This should also be mutex-locked, because each TU is allowed to be in= itialized in a different thread. If the counter values are assigned at compile time, you need to compute eac= h value immediately as the counter updates are declared within the TU. Othe= r TUs are invisible until linking. In order to have consistent counter valu= es, the counting and assignment of the counter to whatever variables need t= o be the same across all TUs that observe the counter or those variables. There is no way to "peek" at things in another TU, because that information= doesn't exist. Maybe the next TU hasn't even be written yet by a programme= r. inline certainly won't help. --=20 ---=20 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 e= mail 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-proposa= ls/. --Apple-Mail=_48C506D6-33DF-4AC5-9FC9-9883D2C39E0D Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=ISO-8859-1
On 2014&= ndash;09–20, at 1:40 AM, Vittorio Romeo <vittorio.romeo.vee@gmail.com> wrote:
On Friday, 19 September 2014 19:23:22 UTC+2, David Kr= auss wrote:
I see some discu= ssion of the ODR in this thread. Any counter usage with linkage does need t= o be placed in the header file and repeated exactly the same in each TU. Av= oid sharing a counter between headers unless those headers are all-or-nothi= ng.

Can you elaborate more on = this? What I am currently doing is putting the workaround code in an header= file (header-only library) and using inline in every function. Is that not= guaranteed to return expected values in different TUs? (values that never = repeat, I mean)

It’s in refere= nce to the StackOverflow answer.

If the counter va= lues are assigned at runtime, it’s sufficient to have external linkag= e (inline or not) on some object or function which does the counting. This = should also be mutex-locked, because each TU is allowed to be initialized i= n a different thread.

If the counter values are as= signed at compile time, you need to compute each value immediately as the c= ounter updates are declared within the TU. Other TUs are invisible until li= nking. In order to have consistent counter values, the counting and assignm= ent of the counter to whatever variables need to be the same across all TUs= that observe the counter or those variables.

There is = no way to “peek” at things in another TU, because that informat= ion doesn’t exist. Maybe the next TU hasn’t even be written yet= by a programmer. inline certainly won’= t help.

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