From: Alexander Terekhov (terekhov_at_[hidden])
Date: 2005-04-07 07:31:02
Peter Dimov wrote:
[...]
> >> and an acquire when the new value is zero.
> >
> > Hmm, tricky. There would be need to be another instruction afterward
> > that creates the acquire barrier. Maybe this would do:
> >
> > __asm__ (" fetchaddl.rel %0=[%4],-1 \n"
> > " cmp.eq %2,%3=1,%0 \n"
> > "(%2) ldl.acq %0=[%4] " :
> > "=r"(rv), "=m"(*pw), "=c", "=c" :
> > "r"(pw) :
> > );
> >
> > Don't ask me whether that's the most efficient way to do this!
That's RAW dependency on a semaphore. It isn't optimal for refcounting
because it equates to a full fence, not mere acquire. BTW, you need a
"memory" clobber clause here (not sure about cc/predicate stuff).
regards,
alexander.