sem_trywait.c\thread\src - musl - musl - an implementation of the standard library for Linux-based systems

#include <semaphore.h>
#include <limits.h>
#include "pthread_impl.h"
int sem_trywait(sem_t *sem)
{
	int val;
	while ((val=sem->__val[0]) & SEM_VALUE_MAX) {
		if (a_cas(sem->__val, val, val-1)==val) return 0;
	}
	errno = EAGAIN;
	return -1;
}