Date: Tue, 25 Mar 2003 21:37:37 -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: <20030326023737.GA85101@attbi.com> In-Reply-To: <XFMail.20030324114810.jhb@FreeBSD.org> References: <20030323074119.GA43849@attbi.com> <XFMail.20030324114810.jhb@FreeBSD.org>
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On Mon, Mar 24, 2003 at 11:48:10AM -0500, John Baldwin wrote: > > http://kernelnewbies.org/documents/kdoc/kernel-api/r287.html > > If you strictly need decrement and test, you can use a while loop > with atomic_cmpset(), e.g. > > do { > x = foo; > } while (atomic_cmpset_int(&foo, x, x - 1) == 0); > if (x == 1) > /* foo just dropped to zero */ > > What task are you trying to accomplish though? 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? Thanks. -- Craig Rodrigues http://home.attbi.com/~rodrigc rodrigc@attbi.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-smp" in the body of the message
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