Subj : Re: Is the following code MT-safe?
To   : comp.programming.threads
From : David Hopwood
Date : Fri Jan 07 2005 04:09 am

tom_usenet wrote:
> if the following code is in a signal handler [in a multithreaded
 > program]:
> 
> //i and j are volatile
> ++i + ++j; //main program code might see them increment in either 
> //order, since there is no sequence point
> 
> ++i, ++j; //program is guaranted to see i increment before j.

You're mistaken, other threads are not guaranteed to see i increment
before j. Remember, the C standard on its own doesn't apply *at all*
to multithreaded code. For this to be well-defined in C+POSIX, POSIX
would have to specify how the statements about volatile in the C
standard apply to memory as seen by other threads. It doesn't, so
those statements are meaningless in such cases. Indeed, real-world
implementations will violate this 'guarantee'.

-- 
David Hopwood <david.nospam.hopwood@blueyonder.co.uk>

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