On Wed, 07 Jan 2009 10:47:03 -0500, redsea <[email protected]> wrote:
When I implement some high performance program in linux 32bit, 32bit
atomic if often not sufficient, for example, If I want to hold a index &
a timestamp to a atomic variable, 32bit is not enough, in 64bit
environment, I can do that.
No you can't. On pretty much all 32-bit systems the double wide Compare
and Swap operation is availible, which allows you to use the index + tag
method to advoid the ABA problem. However, a decent number of 64-bit
systems don't support this operation leaving the vast majority of
lock-free algorithms high and dry. (While there are high order bits you
could hide a tag in, kernel developers are already using them for OS
stuff). Of course, if you're referring to indexing into an array, you can
use two shorts, etc. on 32-bit machines for much the same effect.
