It's not. Locks are created by using CAS, not the other way around. > On a x86 machine the swap basically compiles down to a single assembly > code instruction: > > http://jsimlo.sk/docs/cpu/index.php/cmpxchg.html > > On a normal x86 machine, every lock in the system will boil down to > using this single instruction. x86 has no concept of "locks". Locks > are simply a construct created by the operating system that is > implemented with a series of cmpxchg instructions. This is the reason > this instruction exists in the first place. Every type of > lock/semephore/mutex we need in a operating system can be built off of > this single instruction. This is also why Clojure includes atoms. > > > Ok. Now I understand. So atom wants to take advantage of this hardware high efficiency CAS. Then I agree if the load is not high, atom will be faster than locking. Thanks for pointing this out.
Now I got a broader question, why CAS is hardware supported, but lock is not (i.e., why it is not the other way around)? I used to work on some firmware, and we have hardware mutex. Why this is not generally the case for general purpose CPUs? -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
