Re: [RFC] kern: simple futex for gnumach (version 11)

[Marin Ramesa]

On 01/10/2014 01:59:55 AM, Richard Braun wrote:
> On Thu, Jan 09, 2014 at 09:51:51PM +0100, Marin Ramesa wrote:
> > On 01/09/2014 05:52:21 PM, Richard Braun wrote:
> > >On Thu, Jan 09, 2014 at 05:06:09PM +0100, Marin Ramesa wrote:
> > >> Shouldn't the compare be atomic. Maybe I don't understand what
> > >> atomic really
> > >> means but the GCC manual says this function is. Or is it enough  
> to
> > >> hold the lock.
> > >
> > >From the GCC manual :
> > >"These built-in functions perform an atomic compare and swap. That  
> is,
> > >if the current value of *ptr is oldval, then write newval into  
> *ptr".
> > >So tell us what the point of replacing oldval with itself is.
> >
> > I do a swap so it returns true if they are equal.
>
> I'll say it again because it doesn't look like you got it : when I  
> point
> something out to you, consider you're wrong, and make the effort to
> question your assumptions. You may end up being right at times, but  
> most
> often not. Now please, read your code again, then answer the question  
> I
> asked : "So tell us what the point of replacing oldval with itself  
> is".

OK, sorry. There's no point. I couldn't find just an atomic compare, so
I'm using the compare-and-swap this way. I'll read more in the GCC  
manual,
maybe there is another way.