1 #include "pthread_impl.h"
2 3 static 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 11 hidden int __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 39 int __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 50 weak_alias(__pthread_once, pthread_once);
51