source: azure_iot_hub/trunk/musl-1.1.18/src/thread/sem_trywait.c@ 388

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

int sem_trywait(sem_t *sem)
{
        int val;
        while ((val=sem->__val[0]) > 0) {
                int new = val-1-(val==1 && sem->__val[1]);
                if (a_cas(sem->__val, val, new)==val) return 0;
        }
        errno = EAGAIN;
        return -1;
}