1#include "pthread_impl.h"
2
3static void undo(void *control)
4{
5	/* Wake all waiters, since the waiter status is lost when
6	 * resetting control to the initial state. */
7	if (a_swap(control, 0) == 3)
8		__wake(control, -1, 1);
9}
10
11int __pthread_once_full(pthread_once_t *control, void (*init)(void))
12{
13	/* Try to enter initializing state. Four possibilities:
14	 *  0 - we're the first or the other cancelled; run init
15	 *  1 - another thread is running init; wait
16	 *  2 - another thread finished running init; just return
17	 *  3 - another thread is running init, waiters present; wait */
18
19	for (;;) switch (a_cas(control, 0, 1)) {
20	case 0:
21		pthread_cleanup_push(undo, control);
22		init();
23		pthread_cleanup_pop(0);
24
25		if (a_swap(control, 2) == 3)
26			__wake(control, -1, 1);
27		return 0;
28	case 1:
29		/* If this fails, so will __wait. */
30		a_cas(control, 1, 3);
31	case 3:
32		__wait(control, 0, 3, 1);
33		continue;
34	case 2:
35		return 0;
36	}
37}
38
39int __pthread_once(pthread_once_t *control, void (*init)(void))
40{
41	/* Return immediately if init finished before, but ensure that
42	 * effects of the init routine are visible to the caller. */
43	if (*(volatile int *)control == 2) {
44		a_barrier();
45		return 0;
46	}
47	return __pthread_once_full(control, init);
48}
49
50weak_alias(__pthread_once, pthread_once);
51