Hi Peter, Peter Dimov wrote:
Do __sync_lock_test_and_set and __sync_lock_release work?
__sync_lock_test_and_set doesn't work. __sync_lock_release compiles, but I think it's a NO-OP. My initial thought was, "Why is Peter asking me this? I have already said that it only has swap, so it's obviously not going to support test-and-set!". But I was sensible and checked the gcc docs before posting, and it has this: type __sync_lock_test_and_set (type *ptr, type value, ...) This builtin, as described by Intel, is not a traditional test-and-set operation, but rather an atomic exchange operation. It writes value into *ptr, and returns the previous contents of *ptr. So "test and set" is actually an atomic swap, i.e. exactly what ARM has - but misnamed. Aarggh. If it had the right name I would have noticed it months ago. (I note that gcc blame Intel for the misnaming.) Yet gcc still doesn't seem to implement it. I will go and ask on their mailing list. Regards, Phil.