Re: atomic reference counting primatives.

From: Daniel Eischen (eischen_at_vigrid.com)
Date: 05/24/04

  • Next message: Daniel Eischen: "Re: atomic reference counting primatives." 
    Date: Mon, 24 May 2004 10:50:06 -0400 (EDT)
To: John Baldwin <jhb@freebsd.org>

    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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