Date: Thu, 01 Feb 2001 09:49:14 -0800 (PST) From: John Baldwin <jhb@FreeBSD.org> To: Julian Elischer <julian@elischer.org> Cc: freebsd-hackers@FreeBSD.org, Matthew Emmerton <matt@gsicomp.on.ca> Subject: Re: Atomic bit operations Message-ID: <XFMail.010201094914.jhb@FreeBSD.org> In-Reply-To: <3A791493.FC414DEB@elischer.org>
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On 01-Feb-01 Julian Elischer wrote: > John Baldwin wrote: >> >> On 31-Jan-01 Matthew Emmerton wrote: >> > Hi all, >> > >> > I've taken a look around for an implementation of atomic bit operations in >> > FreeBSD (similar to Linux' asm/bitopt.h, which include clear_bit() and >> > test_and_set_bit()) but haven't found any. The only thing I've found are >> > the atomic clear/set/add/sub routines in machine/atomic.h. >> > >> > Do we have an implementation of atomic bit operations, and if we don't, >> > would we like some? >> >> Erm, atomic_set() sets's bits, and atomic_clear() clear's bits. Anything >> else >> you might need can be done with atomic_cmpset() anyways. Also, atomic >> operations are very hard to debug, esp. to check for race conditions, so >> there >> direct use is discouraged. Instead, use a higher level primitive such as a >> mutex or other appropriate lock. There is also talk of a potential abstract >> refcount type so that simple reference counts can be optimized, though that >> has >> been shot down thus far. > > by who?? I really want this.... Mostly Jason Evans, though Justin Gibbs pointed out that it won't work for all reference counts that one may need, and thus had a problem with having a refcont(9) API that didn't cover all possible refcounts. The current implementation for it can be found at http://www.FreeBSD.org/~jhb/patches/refcount.patch. It's all done with simple atomic operations right now. -- John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/ PGP Key: http://www.Baldwin.cx/~john/pgpkey.asc "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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