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