Date: Wed, 31 Jan 2001 16:06:50 -0800 (PST) From: John Baldwin <jhb@osd.bsdi.com> To: Matthew Emmerton <matt@gsicomp.on.ca> Cc: freebsd-hackers@FreeBSD.org, John Baldwin <jhb@FreeBSD.org> Subject: Re: Atomic bit operations Message-ID: <XFMail.010131160650.jhb@osd.bsdi.com> In-Reply-To: <00df01c08be2$3ff1e0e0$1200a8c0@gsicomp.on.ca>
next in thread | previous in thread | raw e-mail | index | archive | help
On 01-Feb-01 Matthew Emmerton 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. > > Where are these functions implemented? /usr/include/machine/atomic.h just > has atomic_set_XXX and clear_XXX primitives, which work on char/short/longs, > but not individual bits. 1) You need to look in -current. 2) atomic_set_int(&my_int, 4); sets bit _2_ in the integer variable my_int. Make sense? You can't address individual bits on a machine. :-P > I presume that I could wrap the char operations with something that takes > 0x01 and bit-shifts it appropriately so that atomic_set/clear could be used. Hmm, so you mean the API is atomic_set(&foo, x) implies foo |= 1 << x? That means you can't set more than 1 bit atomically, which is a bit limiting. > However, certain other primitives are missing, such as an atomic > test-and-set operation. Under the current scheme this would have to be done > by two independent operations, which is not useful when atomicitiy is > required. do { x = my_int; while (atomic_cmpset_int(&my_int, x, x | foo) == 0); if (x & foo) foo_was_already_set; else foo_was_not_already_set; -- John Baldwin <jhb@osd.bsdi.com> -- 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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?XFMail.010131160650.jhb>