http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52839
--- Comment #12 from Alan Modra <amodra at gmail dot com> 2012-04-04 22:27:43
UTC ---
glibc/ntpl/pthread_once.c:
static int once_lock = LLL_LOCK_INITIALIZER;
int
__pthread_once (once_control, init_routine)
pthread_once_t *once_control;
void (*init_routine) (void);
{
/* XXX Depending on whether the LOCK_IN_ONCE_T is defined use a
global lock variable or one which is part of the pthread_once_t
object. */
if (*once_control == PTHREAD_ONCE_INIT)
{
lll_lock (once_lock, LLL_PRIVATE);
/* XXX This implementation is not complete. It doesn't take
cancelation and fork into account. */
if (*once_control == PTHREAD_ONCE_INIT)
{
init_routine ();
*once_control = !PTHREAD_ONCE_INIT;
}
lll_unlock (once_lock, LLL_PRIVATE);
}
return 0;
}
strong_alias (__pthread_once, pthread_once)
This is quite broken for weakly ordered memory model. Notice how a thread that
sees *once_control != PTHREAD_ONCE_INIT has no barriers at all. That means the
read of *once_control has no ordering with respect to what happened on the
thread that ran init_routine.
