1#include <semaphore.h>
 2#include <limits.h>
 3#include "pthread_impl.h"
 4
 5int sem_trywait(sem_t *sem)
 6{
 7	int val;
 8	while ((val=sem->__val[0]) & SEM_VALUE_MAX) {
 9		if (a_cas(sem->__val, val, val-1)==val) return 0;
10	}
11	errno = EAGAIN;
12	return -1;
13}