Date: Fri, 4 Apr 2003 10:05:18 -0500 From: Craig Rodrigues <rodrigc@attbi.com> To: John Baldwin <jhb@FreeBSD.org> Cc: freebsd-smp@FreeBSD.org Subject: Re: atomic_dec_and_test() in FreeBSD? Message-ID: <20030404150518.GA15112@attbi.com> In-Reply-To: <XFMail.20030326121321.jhb@FreeBSD.org> References: <20030326023737.GA85101@attbi.com> <XFMail.20030326121321.jhb@FreeBSD.org>
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On Wed, Mar 26, 2003 at 12:13:21PM -0500, John Baldwin wrote:
> > I am the port maintainer of the Apache Portable Runtime (apr) library.
> > apr has some atomic functions. For FreeBSD, this is what is defined:
> >
> > /**
> > * decrement the atomic variable by 1
> > * @param mem pointer to the atomic value
> > * @return zero if the value is zero, otherwise non-zero
> > */
> > int apr_atomic_dec(volatile apr_atomic_t *mem);
> >
> > [snip]
> >
> >#define apr_atomic_dec(mem) atomic_subtract_int(mem,1)
> >
> >
> > This is obviously quite wrong.
> >
> > So are you saying that I should replace this with:
> >
> > int apr_atomic_dec(volatile apr_atomic_t *mem);
> >
> > int apr_atomic_dec(volatile apr_atomic_t *mem){
> > apr_atomic_t x
> > do {
> > x = *mem;
> > } while (atomic_cmpset_int(mem, x, x - 1) == 0);
> > if (x == 1)
> > /* foo just dropped to zero */
> >
> >
> > ???????
> > }
> >
> > Can you give more guidance?
>
> You could do this:
>
> apr_atomic_t x;
>
> do {
> x = *mem;
> } while (atomic_cmpset_int(mem, x, x - 1) == 0);
> return (x - 1)
This macro exists on -CURRENT, but I can't seem to find it
on FreeBSD 4.7. What is the equivalent solution on that platform?
Thanks.
--
Craig Rodrigues
http://home.attbi.com/~rodrigc
rodrigc@attbi.com
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