[398] | 1 | #include "pthread_impl.h"
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| 2 |
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| 3 | static void undo(void *control)
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| 4 | {
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| 5 | /* Wake all waiters, since the waiter status is lost when
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| 6 | * resetting control to the initial state. */
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| 7 | if (a_swap(control, 0) == 3)
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| 8 | __wake(control, -1, 1);
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| 9 | }
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| 10 |
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| 11 | int __pthread_once_full(pthread_once_t *control, void (*init)(void))
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| 12 | {
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| 13 | /* Try to enter initializing state. Four possibilities:
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| 14 | * 0 - we're the first or the other cancelled; run init
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| 15 | * 1 - another thread is running init; wait
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| 16 | * 2 - another thread finished running init; just return
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| 17 | * 3 - another thread is running init, waiters present; wait */
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| 18 |
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| 19 | for (;;) switch (a_cas(control, 0, 1)) {
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| 20 | case 0:
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| 21 | pthread_cleanup_push(undo, control);
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| 22 | init();
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| 23 | pthread_cleanup_pop(0);
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| 24 |
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| 25 | if (a_swap(control, 2) == 3)
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| 26 | __wake(control, -1, 1);
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| 27 | return 0;
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| 28 | case 1:
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| 29 | /* If this fails, so will __wait. */
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| 30 | a_cas(control, 1, 3);
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| 31 | case 3:
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| 32 | __wait(control, 0, 3, 1);
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| 33 | continue;
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| 34 | case 2:
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| 35 | return 0;
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| 36 | }
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| 37 | }
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| 38 |
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| 39 | int __pthread_once(pthread_once_t *control, void (*init)(void))
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| 40 | {
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| 41 | /* Return immediately if init finished before, but ensure that
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| 42 | * effects of the init routine are visible to the caller. */
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| 43 | if (*(volatile int *)control == 2) {
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| 44 | a_barrier();
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| 45 | return 0;
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| 46 | }
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| 47 | return __pthread_once_full(control, init);
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| 48 | }
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| 49 |
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| 50 | weak_alias(__pthread_once, pthread_once);
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