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Re: how to use volatile key word?

Cross-posted to 2 groups.

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On Wed, 27 Jun 2012 09:08:08 +0200, David Brown wrote:

> On 26/06/2012 18:10, 伏虎 wrote:
>> how to use volatile key word?
>>
>> Assume I have a global variable shared by two or more tasks.  Do I need
>> to declare it as volatile?
>>
>> When will a non-volatile global variable be written back to memory from
>> a register copy? Before a function call? Or before the return
>> statement?
>>
>>
>>
>>
> 
> You have multi-posted this same question to multiple newsgroups - at
> least comp.lang.c, comp.lang.c++, and comp.arch.embedded.  This is bad
> practice - if you think your question belongs in all groups, you should
> cross-post a single post to all groups.  That way there will be a single
> discussion thread, and the embedded people and language lawyers can
> discuss together.  You are currently getting two sets of opinions as
> seen from wildly different viewpoints.
> 
> You must decide if you are talking about an embedded system or a
> PC-style system.  Are you talking about small, simple processors, or
> large multi-core systems?  Are you talking about interrupt tasks on a
> microcontroller or multiple threads with an OS?  Are you talking about
> small pieces of data (single variables) or large blocks of data?
> Depending on the answers, it could be "yes, volatile is all you need to
> share the data" up to "no, volatile is such a small part of what you
> need that it is not worth bothering about".
> 
> Once you have figured out the right question, and the right details,
> then re-post as a cross-post (or as just a single post, if you think
> only one group is appropriate).  Then we can help give you the right
> advice.

And if the terms "cross posting" and "multiple posting" mean nothing to 
you, check out this Wiki article: http://en.wikipedia.org/wiki/Cross_post.

I had been unaware that the question had been posted to multiple groups: 
yes, you will get wildly different answers, because what's appropriate 
and applicable for an itty bitty processor with code running on bare 
metal is considerably different -- and often diametrically opposed to -- 
what's appropriate and applicable in an application running on a desktop.

Consider a guy in camo pants with a pack full of freeze-dried food, armed 
with a long knife and a shotgun.  Put him in Times Square -- is his gear 
appropriate and applicable?  How about a lawyer in a shiny suit with $300 
shoes, armed with a Visa Platinum?  How's he doing?  Now put those two 
guys out in the sticks in Alaska -- who's gear makes sense now?

Ditto software practices in (deep) embedded vs. desktop.

-- 
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

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Thread

how to use volatile key word? 伏虎 <fuhu314@hotmail.com> - 2012-06-26 09:10 -0700
  Re: how to use volatile key word? Xavier Roche <xroche@free.fr.NOSPAM.invalid> - 2012-06-26 18:56 +0200
  Re: how to use volatile key word? Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-26 12:57 -0400
  Re: how to use volatile key word? Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-26 21:06 +0200
  Re: how to use volatile key word? David Brown <david@westcontrol.removethisbit.com> - 2012-06-27 09:08 +0200
    Re: how to use volatile key word? Tim Wescott <tim@seemywebsite.com> - 2012-06-27 11:10 -0500
  Re: how to use volatile key word? Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-27 10:28 -0700

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