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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