>Basically semaphores were (as far as I know) first >proposed by Dijkstra, and they explicitly imply a "sleep"/"wakeup" >behaviour, ie they are _not_ spinlocks. They originally had operations >called "P()" and "V()", but nobody ever remembers whether P() was down() >>or up(), so nobody uses those names any more. Dijkstra was probably a >bit heavy on drugs or something (I think the official explanation is >that P and V are the first letters in some Dutch words, but I personally >find the drug overdose story much more believable). http://yarchive.net/comp/linux/semaphores.html