Subj : Re: posix and lock-free algorithms
To   : comp.programming.threads
From : David Schwartz
Date : Fri Aug 12 2005 05:21 pm


"Mayan Moudgill" <mmoudgill@sandbridgetech.com> wrote in message
news:11fqai13ktc8930@corp.supernews.com...

 > Actually, it is worse than this. As declared, an ISO standard
 > compliant C compiler is free to reorder, get rid of, and do
 > miscellaneous other optimizations to i and j.

     Of course, but since nobody was talking about an ISO standard 
compliant  C compiler, how is the an issue?

 > ISO/ANSI C has *NO* knowledge of multi-threading or concurrent
 > execution.

     Right, that's why POSIX was created.

 > There are only a couple of requirements  that the compiler has to
 > satisfy:
 > - the optimized code must have the same black-box behavior as the
 > abstract
 > *sequential* machine
 > - volatiles force order w.r.t. other volatiles.

     Umm, no, a POSIX-compliant compiler also has to satisfy the 
requirements imposed by POSIX.

 > Unless you declare i & j as volatile, all bets are off. And all the
 > talk about POSIX (in the context of C) is meaningless, since you're
 > trying to impose a requirement on the code that is not expressible in
 > the underlying language (well, at least not in C)

     That is a totally retarded argument. Every standard that builds on
previous standards add new requirements. The POSIX standard *adds*
requirements to the C standard. So for your argument to work, it would 
have  to have been impossible for the C standard to have imposed such
requirements.

     What utter nonsense!

     DS

.