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Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually

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On Fri, Jul 06, 2012 at 06:11:28PM -0400, Eric Sosman wrote:
> On 7/6/2012 2:01 PM, Uncle Steve wrote:
> >On Sat, Jul 07, 2012 at 09:20:57AM +1200, Ian Collins wrote:
> >>On 07/ 7/12 05:08 AM, Uncle Steve wrote:
> >>>[...]
> >>>This is a concern in my mind right now as I'm writing some posix
> >>>threads code, and so obviously there are a large number of variables
> >>>which ought to be declared volatile.
> >>
> >>What leads you to that conclusion?  That line of though usually implies
> >>you are misunderstanding the relationship between volatile and threads.
> >>
> >>What are you trying to achieve with volatile?
> >
> >Well, I have some data structures that will be accessed from arbitrary
> >threads, so I want to make sure there's no funny business happening
> >behind the scenes where the compiler decides that certain accesses are
> >optional.
> 
>     Although the latest "C11" Standard adds some multi-threading
> support, I'll ignore that because (1) C11 implementations are not
> exactly thick upon the ground as yet, (2) you mentioned you're
> using Pthreads anyhow, and (3) I haven't studied the C11 threading
> stuff closely enough to be a competent commentator. ;-)
> 
>     So: As long as you're using an established non-C-specific
> threading framework, I suggest you visit comp.programming.threads,
> a newsgroup devoted to multi-threading issues.  There you will learn
> that `volatile' is neither necessary *nor* sufficient in connection
> with variables shared between threads.  (You needn't take my word on
> this: Just browse the comp.programming.threads archives and you'll
> see the local experts refuting this misunderstanding every couple
> weeks. It's comp.programming.threads' equivalent of `void main'.)
> 
>     Or, as my first threading teacher put it, "Don't Do That."

Is there are C standard threading framework?

Threaded code is a de-facto reality in today's multi-core environment.
Save for the embedded sector, most systems will run threads in
parallel, and that is that.  C has to recognize this watershed moment
in the refinement of the language.

While the specifics of an implementation within a given operating
system are not C issues, certain common optimizations can be a problem
with certain algorithms, and so there ought to be a C solution to the
problem.  What is it about the volatile attribute that makes it 
insufficient in your mind to the problem presented by threaded code?


Regards,

Uncle Steve

-- 
The moon has never been closer.

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Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Myth__Buster <raghavanil4m@gmail.com> - 2012-07-05 10:44 -0700
  Re: Clarification on the applicability of compile-time optimization to a  struct variable which encompasses a mixture of fields declared as volatile  and non-volatile individually pete <pfiland@mindspring.com> - 2012-07-05 14:59 -0400
    Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Myth__Buster <raghavanil4m@gmail.com> - 2012-07-07 12:53 -0700
  Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-07-05 23:22 +0100
    Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-06 13:08 -0400
      Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Ian Collins <ian-news@hotmail.com> - 2012-07-07 09:20 +1200
        Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-06 14:01 -0400
          Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-06 18:11 -0400
            Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-06 14:33 -0400
              Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Ian Collins <ian-news@hotmail.com> - 2012-07-07 11:29 +1200
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-06 16:27 -0400
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Ian Collins <ian-news@hotmail.com> - 2012-07-07 12:37 +1200
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-06 17:29 -0400
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Ian Collins <ian-news@hotmail.com> - 2012-07-07 15:50 +1200
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-06 19:55 -0400
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-07-07 17:04 +0300
              Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-07 00:10 -0700
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Gareth Owen <gwowen@gmail.com> - 2012-07-07 10:00 +0100
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-07 10:55 -0700
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Joshua Maurice <joshuamaurice@gmail.com> - 2012-07-07 15:13 -0700
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-07 04:40 -0400
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-07-07 17:20 +0300
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-07 10:33 -0700
              Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-07 08:16 -0400
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-07 05:12 -0400
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-07-07 09:24 -0400
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-07 06:07 -0400
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Keith Thompson <kst-u@mib.org> - 2012-07-07 13:26 -0700
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-07 16:04 -0400
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually James Kuyper <jameskuyper@verizon.net> - 2012-07-09 11:14 -0400
          Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Joshua Maurice <joshuamaurice@gmail.com> - 2012-07-06 16:58 -0700
            Re: Clarification on the applicability of compile-time optimizationo to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-06 17:20 -0400
              Re: Clarification on the applicability of compile-time optimizationo to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Joshua Maurice <joshuamaurice@gmail.com> - 2012-07-06 19:39 -0700
                Re: Clarification on the applicability of compile-time optimizationo to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-06 18:54 -0400
                Re: Clarification on the applicability of compile-time optimizationo to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Joshua Maurice <joshuamaurice@gmail.com> - 2012-07-06 20:12 -0700
                Re: Clarification on the applicability of compile-time optimizationo to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-06 19:25 -0400
                Re: Clarification on the applicability of compile-time optimizationo to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Joshua Maurice <joshuamaurice@gmail.com> - 2012-07-06 20:33 -0700
                Re: Clarification on the applicability of compile-time optimizationo to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-06 19:47 -0400
            Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Jens Gustedt <jens.gustedt@loria.fr> - 2012-07-07 15:47 +0200
              Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Uncle Steve <stevet810@gmail.com> - 2012-07-07 06:58 -0400
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Philip Lantz <prl@canterey.us> - 2012-07-14 21:46 -0700
              Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Joshua Maurice <joshuamaurice@gmail.com> - 2012-07-07 16:19 -0700
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Jens Gustedt <jens.gustedt@loria.fr> - 2012-07-08 09:40 +0200
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually James Kuyper <jameskuyper@verizon.net> - 2012-07-08 10:51 -0400
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Philip Lantz <prl@canterey.us> - 2012-07-13 23:25 -0700
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Joshua Maurice <joshuamaurice@gmail.com> - 2012-07-14 14:37 -0700
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Joshua Maurice <joshuamaurice@gmail.com> - 2012-07-14 14:46 -0700
                Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Philip Lantz <prl@canterey.us> - 2012-07-14 21:39 -0700
    Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-06 17:24 -0700
      Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-07-07 02:33 +0100
    Re: Clarification on the applicability of compile-time optimization to a struct variable which encompasses a mixture of fields declared as volatile and non-volatile individually Myth__Buster <raghavanil4m@gmail.com> - 2012-07-07 12:53 -0700

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