source: asp3_tinet_ecnl_rx/trunk/musl-1.1.18/src/thread/pthread_once.c@ 337

#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_full(pthread_once_t *control, void (*init)(void))
{
        /* 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;
        }
}

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 (*(volatile int *)control == 2) {
                a_barrier();
                return 0;
        }
        return __pthread_once_full(control, init);
}

weak_alias(__pthread_once, pthread_once);