51 lines
1.3 KiB
C
51 lines
1.3 KiB
C
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#include "pthread_impl.h"
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static void undo(void *control)
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{
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/* Wake all waiters, since the waiter status is lost when
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* resetting control to the initial state. */
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if (a_swap(control, 0) == 3)
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__wake(control, -1, 1);
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}
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hidden int __pthread_once_full(pthread_once_t *control, void (*init)(void))
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{
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/* Try to enter initializing state. Four possibilities:
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* 0 - we're the first or the other cancelled; run init
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* 1 - another thread is running init; wait
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* 2 - another thread finished running init; just return
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* 3 - another thread is running init, waiters present; wait */
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for (;;) switch (a_cas(control, 0, 1)) {
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case 0:
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pthread_cleanup_push(undo, control);
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init();
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pthread_cleanup_pop(0);
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if (a_swap(control, 2) == 3)
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__wake(control, -1, 1);
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return 0;
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case 1:
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/* If this fails, so will __wait. */
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a_cas(control, 1, 3);
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case 3:
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__wait(control, 0, 3, 1);
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continue;
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case 2:
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return 0;
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}
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}
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int __pthread_once(pthread_once_t *control, void (*init)(void))
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{
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/* Return immediately if init finished before, but ensure that
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* effects of the init routine are visible to the caller. */
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if (*(volatile int *)control == 2) {
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a_barrier();
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return 0;
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}
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return __pthread_once_full(control, init);
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}
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weak_alias(__pthread_once, pthread_once);
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