Date: Mon, 24 May 2004 10:50:06 -0400 (EDT) From: Daniel Eischen <eischen@vigrid.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-arch@freebsd.org Subject: Re: atomic reference counting primatives. Message-ID: <Pine.GSO.4.10.10405241046510.10647-100000@pcnet5.pcnet.com> In-Reply-To: <200405241038.19589.jhb@FreeBSD.org>
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On Mon, 24 May 2004, John Baldwin wrote: > On Friday 21 May 2004 08:44 pm, Garance A Drosihn wrote: > > At 1:56 PM -0700 5/20/04, Julian Elischer wrote: > > >This has been raised before but I have come across uses for > > >it again and again so I'm raising it again. JHB once posted > > >some atomic reference counting primitives. (Do you still have > > >them John?) Alfred once said he had some somewhere too, and > > >others have commented on this before, but we still don't seem > > >to have any. > > > > Btw, does this thread have anything to do with the present > > buuldworld-breakage for sparc64? I notice the compile-time > > errors are something like: > > No. > > > /usr/src/lib/libthr/thread/thr_cancel.c: In function `testcancel': > > /usr/src/lib/libthr/thread/thr_cancel.c:123: warning: passing > > arg 1 of `atomic_cmpset_int' from incompatible pointer type > > > > My guess is that this is related to Mike's change to "Make libthr > > async-signal-safe without costly signal masking. [...etc...]". > > > > This breakage underlines one reason that it would be mighty > > convenient to have some "official" set of primitives. It is > > one thing if a developer has to roll-their-own solution for > > i386, but somewhat more challenging if that solution has to > > work across a half-dozen different hardware platforms. > > atomic_cmpset() is an "official" primitive. The problem is that Mike is using > an enum and assuming that all enum's are ints which is not necessarily true. > The code should perhaps use an int with #define's instead to guarantee that > the variable is an int and not a short, char, or long. You can't use atomic_cmpset() in userland on 386, so if it is being used in libthr, the machine must be checked to make sure it will work, otherwise should fall back to something else... -- Dan Eischen
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