CAS on platforms which provide CAS for lock-free (x86/x64), LL/SC on platforms which provide LL/SC for lock-free (ARM). AFAIK, platforms provide one or the oth

CAS on platforms which provide CAS for lock-free (x86/x64), LL/SC on platforms which provide LL/SC for lock-free (ARM). AFAIK, platforms provide one or the other; not both. So you have to use what you're given.