Re: atomic reference counting primatives.

From: John Baldwin (jhb_at_FreeBSD.org)
Date: 05/21/04

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    To: freebsd-arch@FreeBSD.org
Date: Fri, 21 May 2004 10:02:02 -0400

    On Thursday 20 May 2004 04:56 pm, Julian Elischer wrote:
    > This has been raised before but I've come across uses for it again and
    > again so I'm raising it again.
    > JHB once posted some atomic referenc counting primatives. (Do you still
    > have them John?)
    > Alfred once said he had soem somewhere too, and other s have commentted
    > on this before, but we still don't seem to have any.

    I still have them. Part of the problem is that there are lots of different
    reference counts that work in different ways, and if you try to come up with
    a single all-singing, all-dancing ref count implementation it will be too
    complicated to provide any benefit. What I do think might be useful might be
    a simple refcount() API that is useful for objects that are immutable when
    the refcount > 1 like ucred and are updated via COW. These type of objects
    have a mutex that just protects a refcount and nothing else. Using a single
    refcount op for those objects will cut the number of atomic ops in half. 

    -- 
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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