#include "pthread_impl.h"
#include <threads.h>

#define pthread_cleanup_push_static(f, x) do { static struct __ptcb __cb; _pthread_cleanup_push(&__cb, f, x)

static void undo(void *flg)
{
	once_flag * flag = flg;
	a_store(&flag->__cntrl, 0);
	__wake_priv(&flag->__cntrl, 1);
}

void call_once(once_flag *flag, void (*func)(void))
{
	__THRD_ABI_MARK;

	/* Return immediately if init finished before */
	if (flag->__cntrl == 2) return;

	/* Try to enter initializing state. Three 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 */

	for (;;) switch (a_cas(&flag->__cntrl, 0, 1)) {
	case 0:
		_pthread_cleanup_push((void*)&flag->__cb, undo, flag);
		func();
		_pthread_cleanup_pop((void*)&flag->__cb, 0);

		a_store(&flag->__cntrl, 2);
		if (flag->__waiters) __wake(&flag->__cntrl, -1, 0);
		return;
	case 1:
		__wait_priv(&flag->__cntrl, &flag->__waiters, 1);
		continue;
	case 2:
		return;
	}
}