K 10
svn:author
V 3
kib
K 8
svn:date
V 27
2015-09-08T08:41:07.287627Z
K 7
svn:log
V 666
In the pthread_once(), if the initializer has already run, then the
calling thread is supposed to see accesses issued by the initializer.
This means that the read of the once_control->state variable should
have an acquire semantic.  Use atomic_thread_fence_acq() when the
value read is ONCE_DONE, instead of straightforward atomic_load_acq(),
to only put a barrier when needed (*).

On the other hand, the updates of the once_control->state with the
intermediate progress state do not need to synchronize with other
state accesses, remove _acq suffix.

Reviewed by:	alc (previous version)
Suggested by:	alc (*)
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

END