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Groups > comp.lang.c++ > #67790
| From | "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: "volatile" on variables and current processors |
| Date | 2019-08-19 16:37 -0700 |
| Organization | Aioe.org NNTP Server |
| Message-ID | <qjfbr4$l1t$1@gioia.aioe.org> (permalink) |
| References | <qjf2ec$rph$4@dont-email.me> <qjf7bo$ori$1@redfloyd.dont-email.me> <qjf7dm$ori$2@redfloyd.dont-email.me> |
On 8/19/2019 3:21 PM, red floyd wrote: > On 8/19/2019 3:20 PM, red floyd wrote: >> On 8/19/2019 1:56 PM, Vir Campestris wrote: >>> In the old days volatile on a variable meant putting it in memory, >>> not holding it in a register. That was easy. >>> >> >> No. That's not what volatile means. ISO/IEC 14882:2003 7.1.5.1/8 says >> that volatile is an instruction to the optimizer. >> >> "volatile is a hint to the implementation to avoid aggressive >> optimization involving the object because the value of the object >> might be changed by means undetectable by an implementation." >> >> DISCLAIMER: C++03 is the latest copy of the standard that I have. >> Can someone check a newer version and see if that's still what is >> indicated? > > Also, it's long been known and stated here that volatile is insufficient > for any threading purposes. > Right. Its not portable, they do not imply any memory barrier at all, some things do some don't, it was never meant for threading. Use std::atomic with _relaxed_ membars to read and write volatiles for a device or something.
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"volatile" on variables and current processors Vir Campestris <vir.campestris@invalid.invalid> - 2019-08-19 21:56 +0100
Re: "volatile" on variables and current processors red floyd <dont.bother@its.invalid> - 2019-08-19 15:20 -0700
Re: "volatile" on variables and current processors red floyd <dont.bother@its.invalid> - 2019-08-19 15:21 -0700
Re: "volatile" on variables and current processors "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-08-19 16:37 -0700
Re: "volatile" on variables and current processors Vir Campestris <vir.campestris@invalid.invalid> - 2019-08-20 21:58 +0100
Re: "volatile" on variables and current processors scott@slp53.sl.home (Scott Lurndal) - 2019-08-20 22:18 +0000
Re: "volatile" on variables and current processors Vir Campestris <vir.campestris@invalid.invalid> - 2019-08-22 21:39 +0100
Re: "volatile" on variables and current processors Paavo Helde <myfirstname@osa.pri.ee> - 2019-08-21 09:02 +0300
Re: "volatile" on variables and current processors "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-08-20 23:10 -0700
Re: "volatile" on variables and current processors David Brown <david.brown@hesbynett.no> - 2019-08-21 08:34 +0200
Re: "volatile" on variables and current processors Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-08-21 20:39 +0100
Re: "volatile" on variables and current processors Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-08-21 21:02 +0100
Re: "volatile" on variables and current processors David Brown <david.brown@hesbynett.no> - 2019-08-22 13:30 +0200
Re: "volatile" on variables and current processors Bonita Montero <Bonita.Montero@gmail.com> - 2019-08-21 08:43 +0200
Re: "volatile" on variables and current processors "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-20 02:22 +0200
Re: "volatile" on variables and current processors David Brown <david.brown@hesbynett.no> - 2019-08-20 10:05 +0200
Re: "volatile" on variables and current processors Keith Thompson <kst-u@mib.org> - 2019-08-19 17:08 -0700
Re: "volatile" on variables and current processors Bonita Montero <Bonita.Montero@gmail.com> - 2019-08-20 06:08 +0200
Re: "volatile" on variables and current processors David Brown <david.brown@hesbynett.no> - 2019-08-20 10:14 +0200
Re: "volatile" on variables and current processors Juha Nieminen <nospam@thanks.invalid> - 2019-08-20 13:03 +0000
Re: "volatile" on variables and current processors David Brown <david.brown@hesbynett.no> - 2019-08-20 16:18 +0200
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