Re: atomic reference counting primatives.

From: John Baldwin (jhb_at_FreeBSD.org)
Date: 05/24/04

  • Next message: John Baldwin: "Re: atomic reference counting primatives." 
    To: freebsd-arch@FreeBSD.org
Date: Mon, 24 May 2004 10:38:19 -0400

    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. 

    -- 
John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org
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