How is CAS guaranteed to be atomic? Is it actually implemented by a machine inst...

Freaky · on Aug 29, 2009

Yes, look up cmpxchg and friends.

FreeBSD has atomic.h providing a bunch of different atomic ops, e.g: http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/amd64/include/...

I believe FreeBSD also uses this style of buffer for dmesg, which sadly also results in a lot of interlacing if two kernel threads are trying to write to the buffer at once.

rdtsc · on Aug 29, 2009

Yes, it is implemented by the hardware. In x86 I believe it is the CMPXCHG assembler instruction.

GCC, for example has __sync_val_compare_and_swap(...) function that give you access to the hardware compare and swap.