Re: [boost] New Book: Introduction to the C++ Boost Libraries, Volume I - Foundations

Subject: Re: [boost] New Book: Introduction to the C++ Boost Libraries, Volume I - Foundations
From: Daniel J. Duffy (dduffy_at_[hidden])
Date: 2010-09-22 07:55:05

> Part: 18.13 Volatile Variables

> >  In order to rectify this situation we declare variables to be volatile
> >  in order to disable register optimisations:
> >
> >   // Shared variable
> >   volatile int i2;
> >   // The same functions as above but use a volatile variable.
> >   // Not optimised anymore so results are always correct.
> >   void FV1() { while (true) i2++; }
> >   void FV2() { while (true) cout<<i2<<endl; }
>
> This is so wrong!

Please explain why this is wrong. Is the code wrong? Is the example wrong? Please note that this is a snippet from the full test program where two different threads are started to execute FV1() and FV2().

On my dual-core machine the version without volatile produces wrong results while the version with volatile produces correct results.

 Daniel

 

 

     
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