atomic reference counting primatives.

[John Baldwin]

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 at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org