MFC r328521 (by imp):
Use atomic load and stores to ensure that the compiler doesn't
optimize away these loops. Change boolean to int to match what atomic
API supplies. Remove wmb() since the atomic_store_rel() on status.done
ensure the prior writes to status. It also fixes the fact that there
wasn't a rmb() before reading done. This should also be more efficient
since wmb() is fairly heavy weight.