Subj : Re: Adding thread support for C...
To   : comp.programming.threads
From : David Schwartz
Date : Tue Aug 02 2005 08:29 pm


"Chris Friesen" <cfriesen@nortel.com> wrote in message 
news:11evu9mn4eo0q5d@corp.supernews.com...

> Really?  How would you make the lock/modify/unlock cycle faster than a 
> single atomic increment?

    Who says the CPU *has* an atomic increment? It may only have an atomic 
compare-and-swap.

> In the optimal uncontended case each of the lock/unlock will be an atomic 
> operation, so you end up with one extra atomic as well as whatever 
> modification that you were trying to do.

    Perhaps the CPU has heavily optimized atomic 'lock' and 'unlock' 
operations and its atomic increment is implemented as some kind of 
read/increment/compare-exchange/loop-on-fail thing.

    DS

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