change sem_trywait algorithm so it never has to call __wake

[musl] / src / thread / sem_trywait.c

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

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