But on the Mac, it's not so hopeful:
"Mac OS X does not export interfaces that identify processors or control thread placement—explicit thread to processor binding is not supported. Instead, the kernel manages all thread placement. Applications expect that the scheduler will, under most circumstances, run its threads using a good processor placement with respect to cache affinity."
(http://developer.apple.com/releasenotes/Performance/RN-AffinityAPI/)
Martin